Caterpillars Galore!

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There can be uncountable numbers of tent caterpillars on a single tree. Source:  J.R. Carmichael, Wikimedia Commons

There are hundreds of caterpillars in your yard? Maybe thousands? They’re black with blue marks, a white streak down their back and longitudinal rows of reddish hair? And, above all, every night they gather in a silky shelter commonly called a “tent”? You’re dealing with tent caterpillars, one of the most common—and visible—tree predators.

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The tent protects the caterpillars from predators and rain. Source: Esc861, Wikimedia Commons

There are, in fact, several species of tent caterpillars found in North America and Europe, most in the genus Malacosoma, but there are also other tent caterpillars in other genera. The latter may differ in appearance, but have similar habits. All can do much damage, partially or totally defoliating their host tree.

They’ll attack many species of broadleaf tree, but in home gardens, fruit trees seem to be their favorites. And they don’t just hang out on their host tree, but disperse to other nearby trees and shrubs, returning, however, to their tent each night. Thus, as they wander off looking for a meal each day, you’ll find them in your garden, on your walkways and, just to really freak you out, circling your kids’ sandbox.

Most years, tent caterpillar nests are rather sporadic: you only see a tent here and there and the damage is therefore limited. In other years, however, most host trees in the area will be infested and there may be several tents per tree. In such years (there’s about a 10-year cycle), defoliation can be considerable.

To Treat or Not to Treat?


Tent caterpillars heading back into their nest at night. Source:

In the wild, there is usually no need to intervene. Tent caterpillars are, after all, part of Mother Nature’s plan. A healthy tree can withstand being defoliated occasionally and will in fact cover itself in new leaves just a few weeks later. Also, infestations tend to be occasional: most of the time, they don’t come back to the same tree year after year, which could indeed weaken or kill it. Also, tent caterpillars play an important role in nature as fodder for a wide range of animals, from other insects to squirrels, bats, frogs, skunks and bears. In fact, more than 60 species of birds, including orioles, jays, chickadees and juncos, feed on them in North America alone. So, in a natural site, just let Mother Nature do her thing.

In your garden, though, when they move into an ornamental tree or, even worse, a fruit tree, control may be necessary … and it’s so easy to accomplish!

Their habit of returning each evening to the silky tent they stretch between branches is their weak point! At night, just cut off the branches on which the tent is installed and drop the tent into a plastic bag. Then seal it and put it out with the trash.

Some people recommend burning the nest, but most environmental agencies now discourage this practice for fear that the fire could escape and cause damage.

A Sticky Trunk


A band of sticky glue will prevent tent caterpillars from roaming. Source:

If a nest of tent caterpillars is out of reach, apply Tanglefoot, a glue that never dries, all around the trunk in a band about 6 inches (15 cm) wide. This will at least prevent them from wandering all over your yard. If you prefer not to stain your trunk with glue, surround it tightly with a strip of plastic and apply the glue to the plastic.

BTK to the Rescue



Another possibility is to spray the tree with BTK (Bacillus thuringiensis kurstaki). This organic pesticide is a caterpillar disease widely found in nature and harmless to other insects and animals, including humans. Once the caterpillars ingest the spores, they become ill, stop eating and die about a week later.

Tent caterpillars: after you get over the shock of finding them in one of your trees, you’ll discover they really aren’t the terrible pests they seem!20180620A J.R. Carmichael, WC


9 Reasons Peonies Don’t Bloom

20180619A Renee Firmingham.

Some people have trouble getting peonies to bloom. Read on to learn why! Source: Renee Firmingham.

The garden peony (Paeonia lactiflora) is among the most popular and reliable temperate climate perennials. Most gardeners are more than satisfied with the results they get: their plants bloom in late spring or early summer and produce a profusion of large flowers, often double, frequently delightfully scented. Just the plant they need to decorate their gardens or fill buckets full of cut flowers. And peonies are very long-lived: plants, many still thriving after more than 40 years in the garden, still blooming massively each year, yet require little more care than a bit of hand weeding.

Yet not all gardeners are so successful. Their peonies bloom very little if at all. Let’s take a look at the reasons why:

Problem 1: The Plant Is Too Young


This peony was divided leaving only one eye … and not much of a root, either. It will probably take several years before it blooms. Source:

Peonies are very slow-growing. A newly planted peony plant bought in a typical nursery may well take a year before it first flowers and 3 to 5 years before it’s really starting to bloom heavily. Less mature starter plants, like those inexpensive Chinese imports—or divisions you made yourself with only one or two “eyes” (buds)—can take even longer before they first bloom: 2 to 3 years! And it’s no wonder so few gardeners grow peonies from seed. You probably won’t see the first bloom for at least 3 to 5 years and it will then take them 7 to 8 years before they’re really blooming abundantly.


Be patient! Your plant will bloom … eventually!

Problem 2: Excessively Deep Planting


Peony eyes need to be covered in no more than 2 inches (5 cm) of soil. Source:

When you plant a peony, you have to ensure the eyes are buried, but not too deeply (about ¾ to 2 inches/2 to 5 cm). Never any deeper. Otherwise, the foliage will come out in perfect condition, but there will be no flowers … or very few.


Dig up and replant the peony at the right depth, preferably in early fall (the best time to replant a peony). Or wait. Because a peony planted too deeply will eventually correct itself and grow closer to the surface … but you may have to wait 10 years or more before it blooms.

Problem 3: Mature Peony Transplanted Without Division


It’s best to divide mature peonies rather than replanting them intact. Source:

Peonies simply don’t like transplantation and mature plants, with dozens of long, thick, carrotlike roots carrots, are even less enthusiastic about the idea than younger ones. You’ll often discover that a mature peony (one planted 7 years ago or more) refuses to flower after it’s transplanted, or at least, only does so after several years. Gardeners often find that when they transplant several mature peonies, at least one will begin to flower as if nothing had happened, but the majority are still stubbornly refusing to flower 4 or 5 years later.


Divisions of peonies take moving much better than mature plants transplanted with all their roots and buds intact. Dividing a peony rejuvenates it, in the sense of “making it young again.” Properly done, divisions give renewed, vigorous plants that will likely bloom the following spring. Aim for divisions with three to five eyes. If you divide the plant into smaller divisions than that, with only one or two eyes, you’ll end up with a plant that is too young (see Problem 1) and is not yet ready to bloom. So, instead aim for the middle ground: a peony that is neither a stodgy old-timer nor a wet-behind-the-ears baby: essentially, you want a full-of-pep teenage peony!

To find out when and how to divide a garden peony, read Fall is For Dividing Peonies.

Problem 3: Too Much Shade


In shady spots, stick with the shade-tolerant woodland peony (Paeonia obovata). Source:

Garden peonies are sun-loving plants and do best in full sun in all but hottest climates, where partial shade is better. In most gardens, they’ll still bloom in partial shade, but with fewer flowers and may well have weaker flower stalks. In true shade, though, the common garden peony is a total washout.


Move your peony or reduce the shade, perhaps by eliminating overhanging tree branches. Or plant shade-adapted peonies, such as the woodland peony (Paeonia obovata).

Problem 5: Foliage Removed Too Soon


Leaf peony leaves intact all summer. If you want to cut them back, wait until fall. Source:

After flowering, a peony rebuilds its energy supply and starts to prepare for next year’s flowering thanks to the photosynthesis its leaves carry out. They essentially “recharge its batteries.” Without them, the plant will peter away and die. And the peony is no spring ephemeral: it needs a good three months of foliage to store up the energy needed for next year’s bloom. So, its leaves must be left intact until the end of the season, at least until the beginning of September (in the Northern Hemisphere, that is). If you mow down them on purpose or by accident in July or mid-August, the plant’s ability to rebloom will be severely impaired!


Do not cut back peonies after they bloom. Leave the foliage intact until at least early fall. With many cultivars, the leaves will start to redden in September, a sign that their work is done for that year.

Problem 6: Too Much Fertilizer


Try to keep nitrogen-rich fertilizers away from peonies or else dilute them to safer levels. Source:

It almost never happens that a peony is in soil so poor in minerals that it fails to bloom, but it will fail to bloom if it gets too much fertilizer, especially if the fertilizer is rich in nitrogen (the first of the three figures seen on the fertilizer label). The culprit is usually lawn fertilizer applied too generously right next to the peony.


Peonies are slow-growing plants, not fertilizer-guzzling weeds. With most fertilizers, apply at no more than half the recommended rate. That’s usually quite sufficient, especially if the first digit is greater than 10, as 20-5-10.

Problem 7: Late Frost


A severe late frost can kill peony buds. Source:

The garden peony is actually quite cold hardy and often pulls through late frosts unscathed, but a really deep, penetrating frost at the wrong time, just as the flower buds are starting to form, can kill them, leading to a year without flowers.


If you know that a severe frost is expected just as peony flower buds are starting to become visible (their most vulnerable stage), you can cover the plants with an old blanket or some other cloth, using stakes to support its weight as if it were a tent. Usually, however, it’s easier to stoically accept that sometimes Mother Nature plays dirty tricks on gardeners and wait until flowering resumes the following year. It just isn’t something that happens that often.

Problem 8: Unacceptable Growing Conditions

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Peonies tolerate neither arid soils nor tropical conditions. Source:, &, montage:

Every plant has its specific needs and peonies like rich, deep, fairly loose soil that is always at least a bit moist and has a pH of about 6 to 7. In addition, it’s a temperate climate plant that prefers a slightly cold to very cold winter, growing best in hardiness zones 2 to 7. In extreme conditions, such as a tropical or subtropical climate, severe aridity, rocky soil, very alkaline or very acid soil, or an abundance of invasive tree roots, etc., it will not be a very happy camper and likely will not bloom.


If you don’t have the conditions needed to successfully grow peonies, grow something else!

Problem 9: Diseases


Flower bud killed by gray mold. Source:

Peonies are prone to various diseases, including gray mold or botrytis blight (Botrytis paeoniae), the one most likely to specifically harm blooms. It can kill or damage flower buds, leaving small buds black and dead and larger ones browning and unable to open. It also kills stems and leaves or provokes brown, water-soaked splotches on foliage. Diseases in general and gray mold in particular are especially frequent in cool, wet weather.


Cut off dead flower buds as soon as you see them. The plant still needs at least some of its leaves, though, so even if they are diseased, it may be better to leave the foliage in place for the summer so that what leaf surface is left can carry out photosynthesis, but do cut and destroy them at the end of the season. Applying fresh mulch annually can be helpful: it helps prevent disease spores that overwintered in the soil from migrating back up from the soil to the leaves. Ensure good aeration and good drainage at all times, even if that means you have to transplant your peony elsewhere. If the situation is repeated each spring, either apply a fungicide every two weeks … or give up on peonies.

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Peonies as far as the eye can see: something you just might be able to accomplish! Source: Nichols Arboretum Peony Garden,

There you go! A quick tour of nine reasons peonies fail to bloom. But don’t let the text above scare you off peonies! Yes, there can be problems, but most gardeners have no difficulties at all with their peonies and they come back to bloom massively year after year. You’ll probably find peonies among the easiest perennials you can grow!20180619A Renee Firmingham.

Corn Loves Company


Corn bears male flowers (tassel) on top and female flowers (silks) below. Pollen has to move from the male flowers to the female ones. Source:

Sweet corn or maize (Zea mays saccharata) is essentially the only vegetable pollinized by wind. And for that reason, it should planted in groups so that pollen from the male flowers (in the tassel above the plant) will readily fall on the female flowers below (the silk at the end of each ear of corn). If pollination is poor, the cobs will be deformed with only sporadic kernels.


Corn is usually grown in blocks to ensure good pollination. Source:

Farmers easily solve this problem with massive monocultures: row upon endless row of corn. In the home garden, corn is typically planted in “blocks” (several tight rows forming a square or rectangle) rather than a single row, where pollination might be spotty. However, such a concentration of corn plants tends to attract corn ear worm and other corn insects, not to mention raccoons. That’s why you might want to consider the method Native Americans used: sowing 4-6 seeds together in a tight circle (called a “hill”, although it isn’t necessarily mounded up).


Corn grown in hills as per the Amerindian three-sisters method (along with beans and squash). Source :

The latter technique makes for an attractive effect (corn can be as beautiful as any ornamental grass when grown this way) and allows you to scatter hills of corn here and there throughout your yard, not just in the vegetable patch, but among your flower beds as well, thus avoiding the risks inherent in monocultures. And 4 to 6 plants growing together will ensure good pollination for all the ears.

An ornamental appearance, abundant, productive ears, and good eating: what more could you ask of corn?20180617A

The Best Father’s Day Gift for Gardening Dads  


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You know what I would like for Father’s Day? A helping hand in the garden! A sort of family green team to carry out a few garden chores.

Yes, I appreciate the ties, t-shirts, books and garden tools you’ve given me in the past, even the time you took me out to your mother’s favorite seafood restaurant, forgetting I’m allergic to shellfish. Thank you so much! (The staff at the hospital was very friendly!) But what I’d really appreciate is a helping hand every now and then.

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Source: &, montage

How about slipping a little coupon into that card I know you’ve already prepared, one with a promise to give 2 hours of service in the garden? In fact, slip 3 or 4 coupons into the envelope. That would be about right.

There are always things that really ought to be done in a garden and being a laidback gardener, I don’t even worry much about not being able to accomplish them. But if I could have someone to help me, just a few hours here and there, I could clear up a few things that have been on the “To Do List” for quite some time now. A bit of weeding in the vegetable bed for the under 6s, pruning off some dead wood in the shrub border for the older ones, and for the adults, a bit of heavy lifting we could do together.

Again, if you’ve already gotten me socks this year (again), I’ll be as pleased as punch, but what I really want is help! Pretty please?

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The Most Beautiful Perennial You’ve Never Heard Of


Maryland spigelia is so spectacular in bloom, it’s hard to understand why it is not more commonly grown. Source:

Exotic and stunning, like a fuchsia with upright flowers, Indian pink (Spigelia marilandica), is a modestly sized perennial of wooded areas that creates quite an effect and yet few gardeners have ever heard about it. It’s simply not a household name. Who even knows its family, the Loganiaceae? However, it’s an easy-to-grow plant that is very shade-tolerant (no kidding!) and very hardy (zones 3 or 4 to 9) to boot. I think it deserves to be much better known and much more widely grown.

Try it and you’ll understand why.

What you won’t understand is why this plant is called Indian pink or even woodland pinkroot (an alternate common name)! After all, there is nothing pink about this plant. Its flowers are red and yellow, its leaves and stems are green and its roots are yellow. Where is the pink? However, many plants in the mostly tropical genus Spigelia do have roots that are pink and they gained the common name pinkroot which our plant inherited through its family ties.

Personally, I just call this plant spigelia or, if I have to differentiate it from some other Spigelia species (and that almost never happens!), Maryland spigelia. I just can’t see calling a plant that has nothing pink about it Indian pink or pinkroot!

Understory Plant With Showy Flowers


The surprising and spectacular flowers of Maryland spigelia. Source:

Indian pink (sorry, spigelia) grows in a dense clump about 12 to 24 inches (30–60 cm) in height and 14 to 24 inches (40–60 cm) in diameter. The upright stems appear thin, but are actually very sturdy. They bear opposite ovate to lanceolate leaves, dark green and shiny. There is no petiole and the leaves wrap slightly around the stem at their base.

It’s when the plant starts to bloom that it becomes so impressive. At the tip of the stem a series of 2 to 12 flower buds forms, all on the same side, aligned in single file. They’re green at first, gradually lengthening and swelling towards the top, like an upside-down bowling pin or wine battle, then they turn a rich, intense, eye-catching red. But that’s only the start. Suddenly, the tip of the flower bud bursts open to reveal a star …of pale yellow to greenish yellow! The contrast between red tube and the yellow flower is astonishing!

Spigelia blooms from early to mid-summer, usually for a good four to six weeks. Then the plant becomes a simple foliage plant for the rest of the summer. It loses its leaves in the fall then resprouts the following spring to start a new season of growth and bloom.

What It Wants


It’s a superb plant for shady gardens. Source:

Maryland spigelia is a plant of the woodland, native to the southeastern United States including, of course, Maryland. It does best in a milieu that resembles its natural environment: semi-shade to shade in a slightly moist, slightly acid soil rich in organic matter with plenty of forest litter.

That said, you don’t have to actually grow it in a forest. Spigelia is very adaptable and would be at home—and highly attractive!—in any flower bed. It can easily tolerate full sun, as long as its soil remains at least somewhat moist, and it’s remarkably vigorous in shade. Any well-drained soil will do, but soil rich in organic matter is preferable. To compensate for the lack of forest litter (so rare in flower beds!), cover its root zone with a good organic mulch.

Do be aware, though, that spigelia is not very drought resistant: water it regularly during dry spells.


This is where things get complicated … and explains why the plant is not more common in garden centers. It’s because it’s slow to multiply.

Although when you buy a spigelia, it will probably flower beautifully the first year, it certainly takes its time increasing in size and it can take 7 to 10 years before you feel it’s grown enough to be divided. Sure, the clump does widen over time …but ever so slowly!

Of course, you can produce more plants from seed …but they have to be fresh to germinate well or else stored cool. Letting them dry out will kill them. That’s why few seed companies offer spigelia seed.

You can, however, harvest the seeds from your own plants. But beware, when the seed capsules are ripe, they open explosively, throwing the seeds hither and yon. So, to avoid losing them, place a small bag of tissue around faded flowers to capture the seeds as they mature.

When you do sow them, they’ll need a 2 to 3 month cold treatment followed by warmer conditions in order to germinate well. Spigelias usually start bloom at about 3 years of age.

Another possibility is to simply naturalize a few spigelia plants in wooded area and let them self-sow, something they do modestly but surely. When you see young plants with the same leaves as adults, you can dig them up and transplant them wherever you want.

A Spectacular Pollinator

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The flowers line up in rows like wine cups, inviting hummingbirds for a drink. Source: J. Carmichael, Wikimedia Commons

Maryland spigelia is renowned for its ability to attract hummingbirds. Operation Rubythroat, an international research center helping to conserve the ruby-throated hummingbird (Archilochus colubris), has put spigelia on its list of the 10 best plants to attract hummingbirds. And apparently hummingbirds are its exclusive pollinator: no insects are known to pollinate its blooms.

Toxic, but

I hate bringing this up, but yes, Maryland spigelia is poisonous. All spigelias are. In fact, the Loganiaceae family is fame for its poisonous plants, including the strychnine tree (Strychnos nux-vomica), the plant from which strychnine, dear to Agatha Christie, is derived. Now, Maryland spigelia is nowhere near as toxic as its cousin, but it remains a poisonous plant. You can handle it … just don’t eat it.

Let’s, however, put things into perspective: in your immediate environment, about 40 to 60% of the plants are poisonous or have poisonous parts. That even includes many edible plants (apples, cherries, potatoes, etc.). Also, cases of poisoning due to plants are extremely rare (household cleaning products and medications are far, far more dangerous). Still, it’s better to be aware of the “problem”.

20180616E course, almost every poisonous plant also has medicinal uses and such is the case with spigelia. Native Americans used to employ a root extraction as a dewormer.

Of course, toxicity can also have its advantages for the gardener: spigelia seems resistant to most insects and diseases and deer simply won’t touch it … or will quickly stop after a nibble or two.

Where to Find It?


Maryland spigelia is not so rare you won’t be able to find it. Source:

Maryland spigelia is not the most common perennial, but nor is it so obscure a plant you won’t be able to find it. It’s well enough known that nurseries that specialize in perennials almost certainly offer it and even larger garden centers do carry it, at least occasionally. If you can’t find it locally, there are many mail order nurseries that sell it. Just google the botanical name, Spigelia marylandica, and the word “catalog” and you’ll see.

A beautiful shade perennial just waiting to be discovered: why not try the Maryland spigelia this summer?20180616A

Share Your Surplus Vegetables


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Plant a Row (Plant • Grow • Share a Row in Canada): that’s the title of a program launched by the Garden Writers’ Association Foundation to encourage gardeners to think about planting extra vegetables they can then offer to food banks. It just makes sense: if you grow vegetables for your family, why not produce a few extra to share with the needy? And it doesn’t have to be an entire row, either: if you only have a balcony vegetable garden, one or two extra pots of tomatoes will give you several extra pounds/kilos of produce to share.

And while you’re at it, start a campaign in your neighborhood to get others to do the same. When gardeners get together, they can change the world!

How to Share Your Bounty

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Source: Garden Writers’ Association Foundation

For the name of a food bank or soup kitchen in your area, go to Feeding America (US) or call the United Way Helpline at 211 (Canada).

And once you do locate the nearest soup kitchen, make sure you phone before you show up with your vegetables. The organization may have a day or a time that better suits them to receive donations.

For more information on Plant a Row/Plant • Grow • Share a Row or to start a PAR/PGSR campaign in your neighborhood, contact:

Plant a Row (USA):

Grow a Row (Canada):

Such a simple way to give!

Disease-Free Tomatoes?

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Tomato diseases are rampant these days, but there are ways of combatting them. Source:, &, montage:

It’s not easy being a tomato gardener. The poor vegetable, by far the most popular grown in home vegetable gardens, has more than its fair share of disease problems and growing abundant, healthy tomatoes is becoming ever more difficult. Almost every gardener has been faced with tomato plants slowly (or quickly!) turning yellow or brown starting at the base, a classic symptom of such diseases as fusarium wilt, verticillium wilt and late blight. In fact, tomato diseases have become so common, some gardeners have simply stopped trying and have abandoned tomatoes in favor of easier crops.

Fortunately, there are several easy techniques you can apply—most notably the choice of resistant varieties—that can lessen the damage enough that you’ll be able to enjoy an excellent harvest of juicy tomatoes … without having to spend the summer spraying toxic chemicals. Here are a few suggestions:

1. Avoid Over Early Planting

Tomatoes planted when soil or air are still cool are more susceptible to disease. There are vegetables you can plant out early—spinach, beets, onions, etc. —, but tomatoes are not among them. Wait until both the soil and air have warmed up (nights reliably over 54˚ F/12˚ C) before planting them out.

Growing tomatoes in containers can make things easier, as potted plants can be brought indoors if there’s a sudden cold snap after your tomatoes are planted.

2. A Very Long Crop Rotation

Most tomato diseases overwinter in the soil as spores and are found wherever tomatoes or other plants of the Solanaceae family (peppers, potatoes and eggplants, among others) were grown recently. By changing the planting site annually, you should theoretically be able to avoid them.

For in-ground culture, the tradition has always been a 4-year rotation. The idea is that every year following the initial planting, the number of disease spores decreases. After four years, there should hopefully not be enough viable spores to affect the plants.

Unfortunately, while a 4-year rotation seems good enough for many vegetables, it’s becoming increasingly apparent that it isn’t for tomatoes. There are still live but dormant spores of some diseases up to 10 years later! Logically then, you’d need at least a 10-year crop rotation to be free of tomato diseases … and that’s almost impossible in many vegetable gardens!

Again, container gardening saves the day. Simply replace the soil in the container annually (it can be used for other plants that are not in the Solanaceae family) and thoroughly clean the pots with soap and bleach before using them again. That way you can use the same pots year after year with no decrease in production. (Personally, I no longer even bother growing tomatoes in the ground: container gardening gives me the results I want!)

3. Apply Mycorrhizal Fungi to the Roots


Applying mycorrhizal fungi at seeding or transplanting can help prevent tomato diseases. Source:

Studies show that tomato plants treated with mycorrhizal fungi (beneficial fungi) are more resistant to tomato diseases, especially those that penetrate tomatoes via their roots (fusarium, verticillium, etc.). Commercially available mycorrhizae can be applied when you sow the seeds or plant out seedlings or store-bought plants. You can also buy potting soil that already contains mycorrhizae: very convenient if you sow your own tomato seedlings.

4. Grow Your Tomatoes in Raised Beds

In cool, humid climates, where tomato diseases are especially prevalent, raised beds heat up and dry out faster, helping to prevent disease, most of which spread faster in cool, rainy weather.

5. Give Each Plant Room to Growl

Leave at least 2 feet (60 cm) between tomato plants to ensure good air circulation. Moving air dries the foliage more quickly after rain or heavy dew, helping to prevent disease.

6. Mulch Your Tomatoes

An organic mulch placed on the ground around the tomato plants (yes, right up to the base of the plants, despite a long-standing garden myth that insists mulch should never touch the base of the plants you grow!) will help prevent disease spores that overwintered in the ground from being carried onto the foliage by water droplets hitting the contaminated soil during heavy rains, then splashing onto the plant, their usual means of locomotion. Prefer a mulch rich in organic matter, like shredded leaves or ramial chipped wood.

7. Water the Soil, Not the Foliage


Try not to moisten tomato leaves when you water. Source:

This one should be a no-brainer for any somewhat experienced home gardener, as it’s well known that leaves that remain moist are more subject to most diseases. Of course, you can’t control what Mother Nature does with her rain and dew, but why worsen the situation? When you water, try to moisten only the soil, not the foliage. Or water in the morning. That will allow the foliage to dry out faster than watering at night … and leaves that remain moist all night are highly susceptible to disease.

8. Remove Diseased Leaves

If, despite everything, your tomatoes appear to have yellowing, browning or spotted leaves (symptoms of many diseases), removing the affected leaves may slow the disease’s progress. Wear gloves and sterilize the pruning shears between cuts with rubbing alcohol to avoid transmitting diseases from one leaf to another.

9. Choose Resistant Varieties

Some tomatoes are naturally disease-resistant and are preferable when you have had disease problems in the past. For this purpose, tomato growers and seed companies use letters to indicate resistance. Here are some examples:

V                             Verticillium wilt
F                              Fusarium wilt race 1
FF                           Fusarium wilt races 1 and 2
FFF                         Fusarium wilt races 1, 2 and 3
A                             Alternaria(early blight)
N                             Nematodes
Ph, PHR or LB     Late blight
St                            Stemphylium
T, TMV or ToMV Tobacco mosaic virus

So, tomato varieties with a whole string of letters after their name, such as ‘Big Beef’ VFFNTA or ‘Celebrity’ VFFNT, are great choices for gardeners who have had tomato disease problems in the past. Before buying a tomato plant, always ask the supplier whether it is disease-resistant … and to which diseases.

These resistances seem to scare some gardeners, who take it as a sign that the plant has to be a GMO (genetically modified organism), but these are simply natural resistances that have been united in the same plant by good old-fashioned plant breeding: crossing resistant plants with each other. No OGM is needed!

Note that resistance to disease does not guarantee that the plant will not catch it, especially if the summer is cool and wet or if the soil is thoroughly contaminated with disease spores, but it will at least delay the onset of the infestation, as well as its progress, often allowing you a good harvest even though disease symptoms are starting to appear by early fall.

A Special Case: Tomato Late Blight


A massive attack of late blight. Source:

New, highly virulent strains of tomato late blight (Phytophthora infestans), once a tomato disease of relatively minor importance, emerged in the early 2010s and are now dispersed globally. This sudden upsurge took seed growers and gardeners by surprise, as initially no tomato appeared to be resistant to these new strains (US-23 and, to a lesser extent, US-22). Especially problematic in areas with cool, moist nights, tomato late blight has quickly become the most devastating tomato disease in many areas, including Canada, the north and northeastern US and central and northern Europe.

Also, unlike other diseases that tend to weaken the plant and reduce the harvest, but not necessarily kill it, late blight can kill the plant outright or destroy all the fruits. And it’s a wind-borne disease, so as its spores spread quickly and widely, rather than remaining in the soil where tomatoes were grown in previous years. Therefore, crop rotation has never been very useful in preventing late blight.


Fruit suffering from late blight. Source:

Tomato late blight is best recognized by its symptoms. First, towards the end of the summer (the reason it’s called “late blight”), brown spots appear on the lower leaves and grow quickly until the leaves are completely brown. On the underside of the leaves, the spots may be covered with whitish “fuzz.” Sometimes the top of the leaves and the fruit also show white mold. The disease moves successively upwards, affecting leaf after leaf. Often the stems also turn brown. Even worse, just when the fruit is almost ripe, one or more soft, brown or black depressions form on the fruit and from there on in, it’s only good for the trash.

Fortunately, it turned out that there were tomato varieties highly resistant to late blight and many more have since been bred. This is the case of ‘Mountain Magic’, ‘Mountain Merit’, ‘Defiant PhR’, ‘Iron Lady’, ‘Plum Regal’, ‘Juliet’, ‘Jasper’ and ‘Fantastico’. For a more complete list, go to Yes, Blight Resistant Tomatoes are Possible. If you’ve had problems in the past with this late blight, you should definitely be looking for one of these resistant varieties for your summer garden.

Tomato diseases are definitely an annoyance, but there are now many ways around them. Put them into practice and you’ll soon be growing abundant, healthy tomatoes again!20180614A, &