Aphids on Orchids


Many aphids live on a a wide range of host plants, including orchids. Photo: Ron Parsons, youplants.com

Question: I recently discovered aphids on 2 of my 6 orchids. I’ve had them for almost 2 years and I inspect them regularly. Plus, they’ve always been indoors. Where do these insects come from? Will my other orchids be infected?

Yen Doan

Answer: Aphids can reach indoor plants in several ways.

Since they have a winged phase that usually appears at the end of the summer or in fall, the most obvious thought is that they might have flown in through an open door or window. In fact, though, indoor aphids most often hitch a ride on us (or on our pets)!

When you work outdoors in your garden, or even just rub against an outdoor plant, you can accidentally pick up a few aphids and carry them indoors on your hands or clothes. Since aphids enter diapause (a state of near-dormancy) in the fall, they’re often not noticed at first, but when the days begin to lengthen, they wake up and begin to reproduce. That’s why aphids suddenly seem to appear out of nowhere in midwinter, a situation that has led more than one gardener to believe in spontaneous generation!

Yes, your other orchids can become infected. Ideally, you’d put the affected plants in quarantine in another room until the problem is resolved. And be careful when you handle them! Aphids are easily moved from infected plants to healthy plants when watering, not only on via clothing, but through contaminated tools. For example, they’ll readily hitch a ride on the spout of a watering can.

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Neem and insecticidal soap are both organic products. Photo: Home Depot, montage: laidbackgardener.blog

To control aphids, weekly treatments with a solution of insecticidal soap or neem will be effective provided that all insects, even those hidden in the leaf axils, are reached. It’s therefore important to carefully spray the product on all plant surfaces, even the undersides of the leaves.

And don’t expect the treatment to give instant results. It usually takes 4 or 5 treatments to completely wipe out an aphid infestation.


Ask Questions Before You Buy a Plant


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You’re not interested in constantly fighting against diseases, pests and weeds? Before buying a new plant, therefore, grill the salesperson! Does it have a recurring problem with diseases or insects? Is it invasive? If so, simply choose something else.

Don’t worry this is going to limit your choices all that much! There are dozens of apple trees, for example, which are resistant to scab. Hundreds of hostas which are not attacked by slugs. A decent handful of beebalms (monardas) that don’t try to strangle their neighbors. Even carrots that are resistant to carrot flies! Why then buy a plant that is subject to serious problems?

Prevention is the best medicine: that’s the motto of the laidback gardener!

2019: Year of the Dahlia


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Every year, the National Garden Bureau, a non-profit organization promoting the pleasures of home gardening, selects one annual, one bulb, one perennial and one edible plant to celebrate. It’s a great way to discover a new plant or to learn a bit more about a plant you may already be growing.

Let’s look at the bulb chosen for 2019, the dahlia.

The Plant Behind the Name

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Wild Dahlia coccinea in the hills of Mexico.Photo: Eduardo Ruiz Sanchez, Twitter

There are some 42 species of Dahlia, most from Mexico (its center of diversity), where they generally grow in uplands and mountains. Some species are found elsewhere in Central America, even as far south as northern South America.

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Dahlia flowers are composite, with fertile disc florets and much larger ray florets. The former serve to produce seeds, the latter to attract pollinators. Ill.: sciencejunior.fr & mr-fothergills.co.uk., montage: laidback gardener.blog

They’re in the Asteraceae family, known for its composite flowers, and thus related to such plants as the sunflower, the daisy and the zinnia. Each dahlia “flower” is therefore not a single bloom, but actually a compound bloom, an inflorescence*, composed of multiple small flowers called florets, typically fertile yellow florets forming a central disc surrounded by a circle of variously colored sterile ray florets. The latter are generally called petals by gardeners, but are not true petals.

*In the rest of this text, I’ll use the term “flower” to describe a dahlia inflorescence, according to customary usage.
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Garden dahlias. Photo: Longfield Gardens

The dahlia we know and love (we’ll call it the garden dahlia in this article) is a complex hybrid and its exact parentage is not fully understood. In fact, the plant’s exact botanical name remains “unresolved.” Long known as Dahlia variabilis, modern taxonomists tend to list it as D. × pinnata, the multiplication sign indicating it’s a hybrid species.

The garden dahlia is an octoploid, with 8 sets of chromosomes, whereas most plants have only two. This leads to an enormous multiplicity of genes and thus of possibilities in all the plant’s characteristics: height, leaf color and form, flower color and shape, etc. It’s therefore not surprising that there are some 57,000 cultivars of dahlia, with many new ones created each year. The garden dahlia can range in height from less than a foot (30 cm) to more than 8 feet (2.5 m) with flowers ranging from less than 2 inches (5 cm) in diameter to up to 1 foot (30 cm): the so-called “dinner plate dahlias.” Every flower color but true blue is possible.

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The tree dahlia (D. imperialis), the tallest species, has been known to reach 9 m (30 feet) in height! Photo: http://www.gardentags.com

Along with this great potential for variability comes a lot of genetic instability. Dahlias have many transposons, so-called “jumping genes,” DNA sequences that can change their position and thus change the plant’s appearance. Because of this, dahlias are renowned for their ability to mutate to new forms and to revert to previous forms. Not that this happens every day, but if your red dahlia suddenly switches to being a yellow one, you shouldn’t really be surprised.

The Name Behind the Plant

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Dahlias were originally grown for their edible tubers. Photo: Richard Johnson, http://www.irishtimes.com

The dahlia was well-known to the native peoples of Mexico who grew it for its edible tubers and medicinal uses as well as its hollow stem, using in piping. Indeed, the Aztec name Cocoxochitl means “water pipe plant.”

Francisco Hernández, physician to Philip II, sent to Mexico in 1570 to study the country’s plants and animals, noticed the plant being commonly grown as a vegetable and had a companion, Francisco Dominguez, draw illustrations that were sent back to Spain. Curiously, all had double flowers, practically guaranteeing they were already carefully selected hybrids.

It was Vicente Cervantes, Director of the Botanical Garden at Mexico City, who first sent dahlias to Abbe Antonio José Cavanilles, Director of the Royal Gardens of Madrid. Whether he sent seeds or tubers is unknown, but most likely seeds, as they travel better. Oddly, all the first dahlias actually sent to Europe in 1789 had single flowers. Double flowers later showed up spontaenously in European gardens.

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Dahlia coccinea, one of the first species grown in Europe. Photo: http://www.anniesannuals.com

The plant was originally sent as a possible food source, but that aspect never caught on in Europe. Cavanilles instead saw the plant’s ornamental value. He named the plant Dahlia in honor of Swedish botanist Anders Dahl (1751-1789), calling the three varieties he received Dahlia pinnata for its pinnate foliage, D. rosea for its rose-purple flowers and D. coccinea for its scarlet color. These three plants, plus D. sambucifolia, sent over in 1804, are believed to be the main parents of today’s garden dahlia.

Cavanilles generously shared seeds and tubers with botanical gardens all over Europe and, as a result, by the early 1800s, dahlias were being widely planted in parks and gardens throughout Europe. Also, serious hybridization was going on, notably in Holland and England.

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Josephine Bonaparte, wife of Napoleon Bonaparte, greatly appreciated dahlias … at least at for a while! Ill.: Wikimedia Commons

The royal courts of Europe too were infatuated by these new flowers. Josephine Bonaparte, wife of the French Emperor, was so enamored of dahlias she grew prize varieties in her garden at Malmaison, but refused to share the plants with other nobles. However, eventually a Polish count had one of her gardeners dig up over 100 dahlia plants, then absconded with them. Josephine was so enraged that she had all the remaining dahlias dug up and ground into mulch and, furthermore, banned the flower from her gardens.

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Dahlias presented in the John Lewis Childs seed catalog, New York, in 1895. Photo: http://www.flickr.com

By 1826, over 60 varieties were known and by 1841, one English dealer was offering more than 1,200 varieties. The first garden dahlias reached the United States in the early 1830s and hybridization began there as well. Today, dahlias are grown all over the world and there are many regional and national dahlia societies (national societies include the following: American Dahlia Society, Canadian Chrysanthemum and Dahlia Society, National Dahlia Society (United Kingdom) and Dahlia Society of Australia). And the dahlia is recognized in its native country where it was named Mexico’s national flower in 1963.

Recently, the idea of growing dahlias for their edible tubers has been revived and several hybridizers are working on developing varieties with especially large, prolific and tasty tubers. Maybe they’ll show up in supermarkets along with potatoes and onions some day!

So Much Variety


Dahlias are classified in a bewildering number of groups. Photo: justfunfacts.com

There is an astounding amount of variety among dahlias, although how they are classified varies a bit from one dahlia society to the next. Among the terms you’ll run into if you grow dahlias are the following:

Anemone: broad outer ray florets and a central “pincushion” of tubular disc florets, usually of a different color.

Ball: fully double flowers with blunt-tipped ray florets.

Cactus: highly rolled-up, very pointed ray florets, giving the appearance of cactus spines.

Collarette: semi-double with flat ray florets, a central yellow disc and, in between, shorter petaloid stamens forming a collar.

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‘Sagitta’ is a formal decorative dahlia. Photo: Van Zyverden Inc.

Decorative: fully double uniform flower with fairly flat ray florets (petals). Formal decorative flowers have rounded tips; the ray florets of informal decorative flowers have rolled tips.

Fimbriated: ray florets that are deeply notched.

Novelty or Miscellaneous: flowers that don’t fit into other classifications.

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Orchid dahlias, like ‘Honka Surprise’, actually look nothing like orchids. Photo: http://www.jparkers.co.uk

Orchid: single flower with tightly rolled ray florets.

Peony: semi-double with an open center and two or three layers of ray florets, looking much like a peony flower.

Pompon: like Ball, but with miniature flowers.

Semi-cactus: like a cactus flower, but with ray florets broader at the base.

Single: single flowers, i.e. a single row of ray florets surrounding a central disc.

Stellar: like a cactus flower, but curled so the reverse of the ray floret is showing.

Waterlily: double flowers with broad but fairly sparse ray florets looking overall like a waterlily blossom.

There are many more terms and definitions, but that should be enough to get you started with your dahlia collection.

Growing Dahlias

Dahlias are frost tender and should not be planted out until all risk of frost has passed and both the soil and the air have warmed up. One guideline is to plant at the same time as you would a tomato.

Plant them in full sun (partial shade is grudgingly accepted) in rich, well-drained, slightly acidic soil, in the garden or in containers. Plant the tubers with the crown just below the surface of the soil and water in. Give dahlias started in pots or trays similar treatment.

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In some climates, it can be useful to start dahlias indoors. Photo: gardeninginthelines.wordpress.com

You can also start dahlia tubers indoors in pots, placing them in full sun or under lights under normal home temperatures, for a bit of an advance on the season (especially useful in short-season areas).

Dahlias are quite heavy feeders and will appreciate extra minerals through the summer, although they aren’t particular as to any specific formula. Probably the easiest thing to do is to apply an all-purpose slow-release fertilizer at planting to carry them through the summer.

Monitor soil moisture, especially if the local rainfall is less than 1 inch (2.5 cm) per week. In containers, dahlias will require more water because of their limited soil volume.

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There are many ways of staking dahlias. Photo: stonehousedahlias.com

Taller types, especially those with large flowers, will need staking. Traditionally, you would hammer a simple wooden or bamboo stake as long as the plant is tall into the ground before you place the tuber into the planting hole. That way there is no risk of accidentally damaging the tubers. I find it simpler to place a tomato cage over the plant after planting.

Deadhead (remove faded flowers) to help maintain constant flowering. True enough, there are a few modern dahlias are self-cleaning, especially among dwarf and semi-dwarf bedding type dahlias. With them, no deadheading is necessary, the ideal situation for laidback gardeners, but sadly, they still remain a minority.

Many dwarf varieties are not influenced by day length and will bloom all summer. Taller dahlias tend to bloom from late summer into fall.

Overwintering Dahlias

In their native land, dahlias grow in mountainous areas with a dry, fairly cold winter and have learned to go dormant at that season. The top of the plant dies back while the tuberous roots are safe from the cold underground, then sprout again in spring when the weather warms up and rains return. In the garden, you have to maintain the same cycle.

Only in mild climates (hardiness zones 8 to 11) with fairly dry winters can you consider leaving dahlia tubers in the ground all winter. For aesthetic reasons, cut the tops back to near ground level when the plants stop blooming and the foliage dies back. Applying a good thick mulch is wise if there is any danger of frost.


Most gardeners dig up their dahlias in the fall and bring the tubers indoors for the winter. Photo: theflowerbincolorado.blogspot.com

Gardeners in colder climates or rainy mild ones will have to dig them up in the fall. Since the tubers really began to put on growth when days shorten, the longer you leave them in the ground without risking the ground freezing hard, the bigger the tubers will be and the better they’ll survive the winter. In many areas, you can wait until a killing frost has blackened the foliage before proceeding.


Rinse the tubers, then let them dry thoroughly before storage. Photo: http://www.cooltropicalplants.com

When you’re ready to do so, cut back the stems to about 4 to 8 inches (10 to 20 cm) in length, then dig up the tuberous roots using the stems as a handle. Shake as much soil free as possible, then rinse well with water to get most of the soil off. Spread the plants out and let them dry out for a few days in a garage or tool shed. Make sure you carefully label the each variety so there’ll be no confusion come spring.

Now store the tubers for the winter, ideally in a cardboard box, wooden crate or a well-aerated plastic container. Just barely cover them in vermiculite, sand, wood chips or peat, then place the containers under cool conditions (less than 50 °F/10 °C), but above freezing. If you store them at room temperatures, check frequently for dehydration

Check monthly for signs of rot and dehydration. Remove rotting tubers, of course. If any tubers start to become wrinkled, a sign they’re dehydrating, give them a quick spritz of water to plump them up again. By late winter, sprouts will be appearing from the crown and it will soon be time to start the tubers for a new growing season.

Multiplying Dahlias

There are several ways of multiplying dahlias, including from cuttings, tuber division and seed.

Stem Cuttings

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Dahlias are easily grown from stem cuttings. Photo: http://www.cooltropicalplants.com

The advantage to taking stem cuttings is that you can rapidly produce many plants of the same cultivar. Oddly enough, cutting grown plants usually come into bloom earlier than tuber-grown plants!

You can take cuttings at just about any season when the plant isn’t dormant as long as you remove any flowers or buds present on the stem. However, the best season is early in the year, when sprouts are just coming up from the tubers, as this will give you plants that will bloom the same summer. There’ll be several to many shoots per tuber, so little harm comes from harvesting a few. In fact, if your plant produces more than 5 shoots, you should remove the excess ones anyway.

When the stems have about 3 to 4 pairs of leaves, cut them off at the base and insert the cut end into moist potting soil, making sure at least one node is covered in mix. No rooting hormone is necessary. Cover with a clear plastic dome or bag and place at room temperature in moderate light (no sun at first, otherwise it will become too hot) or under lights. When you see new growth, a sign that stems have rooted, remove the covering and move to full sun, then harden off before planting out for the summer.

Dividing Tubers

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Make sure each division has an eye. Photo:  www.scdahlias.org

This is the classical way of starting new dahlias. It can be done in fall, as you bring them in for the winter, or in spring, just before you plant them. The tuber is a thickened root and provides the energy for new growth, but new growth itself comes not from the roots, but from the base of the stem (its crown). Therefore, you can’t simply cut the tubers free: if you do, nothing will grow. You need a tuber with a piece of stem attached that bears an eye (bud). Often, you’ll end up with one eye and two or more attached tubers.

Experienced growers usually divide their tubers in the fall, when the stems are soft and easier to cut, but then, they’re able to recognize the beginning of an eye. For beginners, I suggest waiting until spring. By then, the eyes will be well formed, even sprouting, although you may need to saw through the hard stems with a serrated knife to separate the divisions or use a lopper (the long handles give you greater force); pruning shears may not be powerful enough.


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Bedding dahlias are as easy to grow from seed as any other annual. Photo: http://www.unwins.co.uk

Garden dahlias will not come true-to-type if you harvest their seed, therefore if you want to multiple a valuable variety, seeds are not the way to go. However, you can find commercially produced dahlia seed lines that are quite stable and will give excellent results. You just won’t have as wide a range of choice as with tuber-grown plants. Most dahlias grown from seed are dwarf or semi-dwarf varieties used as bedding plants, the idea being to produce lots of plants cheaply. They’re usually treated as annuals and tossed at the end of the growing season, but of course, you can recuperate the tubers and grow them again if you wish

Start the seed of bedding varieties indoors about 6 to 8 weeks before planting out (8 to 10 weeks for taller types). Sow the fine seeds very shallowly, about 1/8” (3 cm) deep in a lightly moistened seedling mix and cover with a clear plastic dome or bag. Place in moderate warmth (65 to 79 °F/18 to 26 °C) until germination, then remove the covering. Place in bright light to full sun or grow under lights (ideally, at 12 hours or more a day, as long days stimulate growth and flowering, while short days stimulate tuber growth and can lead to early dormancy), transplanting into individual pots when the leaves begin to touch. Always keep slightly moist. If seedlings seem slow to branch, pinch out the top pair of leaves to produce a bushier plant.

Acclimatize to outdoor conditions and plant out, as mentioned, at tomato planting season.

Cut Flowers

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Dahlias used as cut flowers. Photo: http://www.whiteflowerfarm.com

Dahlias make outstanding cut flowers. To make them last longer, harvest when the flower is open but not yet fully mature. Certainly avoid flowers still in a tight bud: they won’t open after cutting. Also, for maximum durability, prepare the flowers by plunging their stems into very hot tap water immediately after harvest, then letting them cool for an hour before you start arranging using fresh water. Of course, change the water every few days.


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Bees are attracted to single and semi-double dahlias. Photo: honeybeesuite.com.

Dahlia flowers are highly attractive to a wide range of pollinators, including both native bees and honeybees. They prefer open-faced flowers, that is single and semi-double dahlias where the central disc of yellow florets is fully exposed. Double dahlias are not the best choices for pollinator gardens.

Protecting Your Plants From Pests

Small dahlia plants are susceptible to slug damage. It is a good idea to manually remove slugs or to protect them with commercial slug bait.

Japanese beetles seem to enjoy dahlia blooms just when they are ready for a bouquet. One of the best methods of control is to manually remove the beetles and drop them into a bucket of soapy water.

If other insects such as earwigs, thrips, or aphids become a problem, you might want to consider using an insecticidal soap or a commercial pesticide. Follow label directions carefully when using any pesticide

Deer problem? Dahlias are low on the deer’s list of favorite foods. While dahlias are not “deer-proof,” they are deer resistant.

Where to Find Dahlias?

Where not to find dahlias! You’ll find them everywhere that seeds or plants are sold: garden centers, farmers’ markets, supermarkets, etc. They’ll be in stores from late winter right through spring.

Here are some of the mail-order sources recommended by the National Garden Bureau.

Dahlias: few other garden flowers have so much to offer!


New Name for the Garden Writers Association


With the coming of the New Year, the Garden Writers Association (GWA) has taken advantage of its 70th anniversary to update its name. It is now Garden Communicators International and will be known as GardenComm.

This name change has been a long time coming.


This was long the logo of the Garden Writers Association.

It’s been apparent for years that the name “garden writers” simply didn’t cover it all. Many of its members are photographers, artists, lecturers, garden tour hosts, horticultural consultants, podcasters, PR people for public gardens and the horticultural industry or work on radio or television. All do reach out to gardeners to share information, but they don’t all write. Even garden bloggers—and there are many of us!—often don’t, for some reason, seem to consider themselves writers. So, a more comprehensive name was needed … a name like Garden Communicators International, GardenComm for short. Because all of us (yes, I’m a member!) communicate about gardens and gardening. It’s what we do and it’s what brings us together!

I’ve been a GWA member for over 30 years. In fact, I’m a past president of the association and have held all sorts of offices within GWA over the decades, including chairing the Local Arrangements Committee for the Quebec City symposium in 2013.

I can still recall how surprised I was to learn there was actually an organization for people like myself who made their living communicating about gardening. I was, in 1983, just starting my career, writing freelance about my passion for gardening for a newspaper and a few magazines and beginning to give lectures. I had no idea what I was really doing and whether you could actually make a decent living at it (I certainly wasn’t at that point). Then, while I was in Miami for the World Orchid Conference, I heard that there was a “Garden Writers Association of America” meeting in the hotel just across the street, so I wandered over … and met the friendliest people I’d ever run into to in my life. They just welcomed me in (well, I did have to pay admission, of course!) and presented me around. To my astonishment, I found myself hobnobbing with famous authors (well, famous in the gardening world) who treated me like I was one of them! And, I now realize, I was!

I ended up skipping the rest of the orchid show and spending the final part of my trip attending outstanding lectures, visiting extraordinary gardens and simply socializing with this new group of like-minded people (we’d call that networking today). I was hooked!

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Don’t miss the 2019 Annual Conference and Expo.

It was thanks to GWA that I got my first book contract, that I learned how to put together a decent PowerPoint presentation, that I learned the tricks of the trade of being a garden speaker, that I was able to pick up the latest gardening news and trends and that I simply developed the reassurance that what I dreamed of doing—making sharing my passion for gardening my life’s work—was indeed a viable way of life. And every year I attend the annual conference and exposition, wherever it takes place (it will be in Salt Lake City in 2019!), to reconnect with old friends, meet new ones, pick up new information and visit exclusive gardens. I owe GWA—now GardenComm—all my gratitude.

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Visiting outstanding gardens is one of the main draws of the annual conference and expo.

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On the QT, GardenComm’s bimonthly newsletter.

Are you a garden communicator? Do you blog, write about gardening for a local paper, share information about gardening in other ways? Why not consider joining GardenComm? At $105 US for a year’s membership, that’s a whole lot less than just about any other professional organization (indeed, I spend more every year on seeds!) and you certainly get your money’s worth. And tell them the Laidback Gardener sent you, for…

I am GardenComm!

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Larry Hodgson

Seed: Sow Thyself!


Common stork’s bill seed planting itself. Photo: p. roullard

The seeds of the common stork’s bill (Erodium cicutarium), a sticky, hairy annual weed closely related to geraniums (Geranium) and pelargoniums (Pelargonium), sow themselves.

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Erodium seeds with awns tightly coiled and nearly uncoiled. Photo: Didier Descouens, Wikimedia Commons

The seeds are launched abruptly into the air by a springlike mechanism, landing up to 3 feet (1 m) from the mother plant. Since they also bear feathery parachutes, they can travel even further on a windy day. But what is really interesting is what they do when they land.

In the video, you see the awn both uncoil as it pushes the seed into the soil, then coil and uncoil several times as it adjusts the seed depth. Video: p. roullard

Each seed bears a long bristle called an awn. It is spiral-shaped and begins to curl into a tight springlike shape in response to dry air. As the air becomes moister, it does the opposite, uncoiling. As it does so, the action drills the seed into the ground, effectively sowing it. If the seed isn’t sown deep enough, the awn will twist up yet again in dry weather, then do some more drilling when the air moistens, repeating the action several times if needed.

A seed that sows itself? How neat is that!

Hoyas: Be Careful What You Prune


Hoya in bloom. Photo: pistilsnursery.com

The hoya or wax plant (Hoya carnosa and similar species) is an attractive indoor climbing or hanging plant with thick waxy leaves. Fairly easy to maintain, it can, however, be slow growing and especially slow to bloom. Usually, it takes at least 2 years before you see the first flowers and that’s when it grows under ideal conditions (bright light, warm temperatures all year and moderate watering). Most people report seeing the first flowers only after about 5 years. Under low light, it will likely never bloom at all.

The good news is that once a hoya does begin to bloom, it will usually bloom every year from then on … but only if you’re very careful where you prune it!

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Spur several years old showing new flower buds at the tip. Photo: jdeeannsblog.blogspot.com

Its pretty umbels of attractive and fragrant flowers are borne on a short stalk (spur) that remains on the plant after blooming. From then on, the plant will continue to bloom from the same spur, which elongates a little every year.

So be careful not to damage the spur when removing faded flowers and, if you need to prune your hoya, try not to remove the spurs, otherwise you’ll be eliminating future blooms!

Insects That Spread Plant Diseases


Some pretty innocent-looking insects can transmit some pretty powerful plant diseases. Ill.: laidbackgardener.blog

Insects that feed on the sap or scrape or munch on the leaves of our garden plants sometimes have much more serious consequences than just a bit of leaf damage. They may well be carrying an incurable plant disease that will cause more damage than the insect itself ever did.

This isn’t so surprisingly, really. It’s well known that mosquitoes transmit malaria, dengue fever and Zika virus to people. That other insects do the same to plants is a similar process.

Plant viruses and their relatives, viroids and phytoplasmas, are mostly transmitted by insects that inject them into plant tissues as they eat. However, there is no treatment for viruses in the home garden except to pull out and destroy infected plants. That’s why it’s important to act quickly when a plant is attacked by any insect in the hopes of removing the pest before it has time to spread its deadly cargo.

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Spittlebugs look fairly innocuous, but are a major vector of plant diseases. Photo: extension.entm.purdue.edu

Among the insects that commonly transmit viruses are aphids, flea beetles, leafhoppers, whiteflies, thrips and spittlebugs (froghoppers).

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Mosaic virus is one of the more visible viruses. Photo: DieterO, Wikimedia Commons

Viruses (and other related diseases) sometimes have visible symptoms: for example, a specific discoloration of the leaf (mosaic or marbling) or deformed foliage or flowers, but most often not … except the plant weakens and becomes less productive. The two classic cases are strawberries and raspberries. Both are very productive for 2 to 5 years, then go so far downhill due to multiple viral infections that the only logical solution is to destroy them and start anew with “indexed” plants (plants confirmed to be free of viruses).

A good way of reducing the attacks of virus-carrying insects in the home garden is to maintain a good biodiversity in your plantings. Monocultures, where a single plant species is grown over a large area, attract and retain predatory insects of the crop being grown. When plants are grown in mixed plantings, though, these insects have a harder time finding their favorite host and your plants are therefore less often infested with debilitating diseases.

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Nasturtium used as a trap crop. Photo: http://www.nature-and-garden.com

If you add a trap crop to your garden, that is, a plant the insect pest likes even better than the crop you want to protect, such as the nasturtium (Tropaeolum majus), an excellent trap crop for aphids, prevention can be even more effective: just yank out the trap crop at the first signs of infestation, before the insect can spread to neighboring plants.