Garden Myth: Pine Needles Acidify the Soil

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Popular belief to the contrary, pine needles have almost no influence on soil acidity. Photo: sphere

There is a very common and persistent garden myth that pine needles (and other conifer needles) acidify the soil and therefore should not be used as a mulch or added to the compost bin.

The belief behind this myth is that they are very acid and will make the soil too acidic for most plants. Some gardeners even mix pine needles into the soil of their acid-loving plants, such as rhododendrons, heathers, blueberries and blue hydrangeas, convinced they will make the soil more acidic. However, they’re wasting their time. The fact is that pine needles have almost no effect on soil acidity.

Not So Acidic

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Pine needles used as a mulch. Photo: Charles Rondeau,

There are two main reasons why pine needles don’t acidify soil to any degree and the first is that they are simply not that acidic!

In fact, although fresh green pine needles are generally quite acidic, they’re already less so when they turn yellow (their condition when they fall off) and much less so when they finish decomposing. If you analyze the pH* (degree of acidity) of brown, fairly decomposed pine needles, it’s usually between 6.0 and 6.5 … more alkaline, in fact, than rainwater (it normally has a pH of about 5.6). And the ideal pH for most plants is between 6.0 and 7.0. In other words, by the time they finish decomposing, pine needles are about spot on perfect for 95% of all the plants you might want to grow. Where’s the problem?

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*The pH scale goes from 0 (extremely acidic) to 14 (extremely alkaline), with 7 being neutral. Illustration:

Not Much Influence

The other factor is that soil pH is very stable. Several agents, including the soil’s microfauna, act as buffers to stabilize soil pH. Changing the pH of a soil is very difficult and requires significant applications of acidifying products, such as sulfur, or alkalinizing products, such as lime. In addition, the soil tends to return to its original pH if repeated applications are not made. Whether you like it or not, it’s largely the bedrock below that determines the pH of the soil in which you garden and changing it is never going to be easy.

The application of pine needles—or any other mulch or soil amendment resulting from the decomposition of plant material—will only have such a minor effect on the soil’s pH, even after years of repeated applications. In fact, in most cases, the effect will be so minor that most pH test kits won’t be able to detect it.

Easy Enough to Prove

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Soil tests easily show that pine needles have little to no effect on soil pH. Photo: Lynette, Flickr

It’s easy to prove that the pH of soil is not much influenced by the presence of pine needles. Do a soil test under a mature pine tree that has been showering the ground with needles for years and do another under a deciduous tree in the same area and the same soil type, one that doesn’t have the reputation of acidifying soil. The pH will be substantially the same and indeed probably identical.

But Why Don’t Plants Grow Well Under Pine Trees?

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Not many plants grow under pine trees, but it’s not because of the soil’s acidity. Photo: Hans Rohr, Wikimedia Commons

I know that many readers will object to the information above, insisting that pine needles must necessarily make the soil very acidic, otherwise how can you explain the fact that so few plants grow well under pine trees? But you have to remember that excessive acidity is only one factor that can stunt plant growth.

Try digging a hole under a pine tree and you will quickly understand the main reason why plants grow poorly there. Pines (and most other conifers) produce very dense, very superficial roots reaching out in all directions like the spokes of a wheel. These roots quickly absorb any rainwater that falls and any minerals available in the soil. The soil under a pine is therefore in a permanent state of drought and mineral deficiency. Few plants do well under such hostile conditions. This factor alone largely explains the paucity of vegetation under pine trees.

But there is another important factor: shade. Little light gets through the dense needles of most pines … and low light is simply not conducive to the growth of green plants.

A Popular Mulch


Bales of “pine straw.” Photo:

In areas where the “pine-needles-acidify-soil” myth has not taken hold, pine needles are sold as garden mulch. In fact, it’s often the most popular mulch, both effective and attractive. It’s sold in bales, often under the name “pine straw.” I never see pine straw sold in my area, where the “pine-needles-acidify-soil” myth is very strong, yet there are plenty of pine plantations that could yield a ready supply of inexpensive mulch.

Do note though that, in spite of other qualities, pine straw is highly inflammable and therefore should not be used as a mulch where forest fires are a concern.

Oak Leaves Too

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Oak leaves have no more effect soil acidity than pine needles, but I’d suggest shredding them with a lawn mower before use, otherwise they are very slow to decompose. Photo: tracy, Wikimedia Commons

The information above about pine needles largely applies to oak leaves, also often accused of being too acidic for gardening purposes.

Again, oak leaves are not all that acidic to start with and they too decompose into perfectly fine compost with a very reasonable pH. But in fact, that is of limited importance. What you really need to remember is that the natural pH of any soil is very difficult to change and that decayed or decaying vegetation of any type, whether left on the surface or worked into the soil, simply won’t have much influence on it.

So go ahead and use pine needles or oak leaves if they are available to you. Mother Nature put them there to be recycled … and you never go wrong by following her cues!20171010A pxhere


Don’t Cut Back Ornamental Grasses in Fall


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Grasses can create absolutely phenomenal vistas in winter… if you leave them standing! Photo: Max Pixel

Many gardeners like to “clean up” their gardens in the fall (read Are You an Excessive Gardener or a Laid-back One?), but pretty much everyone agrees that ornamental grasses should be an exception to that rule. While most turn different shades of beige and brown as the season advances, they still remain attractive. Their feathery flower heads generally turn an attractive silver color and remain on the plant over the winter. Against a background of snow, they are very attractive indeed.

Even grasses grown as annuals, like purple fountain grass (Pennisetum x advena ‘Rubrum’), which is subtropical (hardy only to zones 9 and above), looks perfectly charming when leaves and feathery flowers have turned beige and can certainly be left standing all winter.

Plus the seeds of ornmental grasses are a major food supply for birds… and you wouldn’t want to be accused of starving our fine feathered friends, would you?

When spring comes around, just cut grasses back to the ground and the perennial ones will soon start to sprout anew.

Should You Compost Diseased Leaves?

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This Norway maple leave nearly covered in tar spot would nevertheless make it into my compost pile. Photo: Cephas, Wikimedia Commons

Composting fall leaves with disease symptoms (maple tar spot, powdery mildew, apple scab, etc.) is a very controversial subject. Even gardening experts have widely divergent opinions on the subject.

Some recommend that you not compost diseased leaves. They insist that diseases can survive the composting process and then return to infest your plants the following year. These experts recommend instead that diseased leaves be burned (where that is legal) or composted by the municipality (most have industrial composting systems that heat up much more than the average home system, to 160 ° F [70 ° C], and thus kill any spores present on the leaves).

Others say that although leaves decompose more slowly at the relatively cool temperatures of the average composter, when the compost is finally ready, the spores will have been destroyed. Any survivors will be so weakened as to be ineffective in finding their host species. Plus leaf disease spores are already so widely disseminated in nature that what you do with your leaves essentially makes no difference. If the conditions are right for the disease to develop, it simply will. That being the case, why not put the diseased fall leaves and in fact any diseased plant material in the compost?

There you go: two widely divergent views. So who are you to believe?

What I Do

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I don’t hesitate to use fall leaves, whether diseased or not, not only in my compost, but as a mulch. Photo: Flash Alexander,

I don’t pretend to have a PhD in plant pathology, but I do garden and have done so all my life. And I’ve always put any plant refuse that is logically compostable*, both diseased and healthy, into the compost pile. I make no exceptions: everything gets composted! Even plants with invasive rhizomes and weeds bearing seeds, which we’re always told not to compost, go into my compost pile. If I see a living rhizome or seeds start to germinate in my compost bin, it’s simply a sign that the compost isn’t ready. So I “turn” the box’s contents (mix the different levels) yet again to aerate it, then wait until Mother Nature finishes her work of decomposition. She can be slow, but she is effective.

*I don’t put corn cobs or large pieces of wood in the compost: they decompose far too slowly for my needs.

Now, I’ve always composted diseased leaves as did my father before me (there was always a compost pile back behind our house and we tossed all our plant refuse into it). As far as I know, this has gone on in my family for generations. There was no question of not including diseased leaves in the mix. In fact, they’re the first ones to go into the pile, removed so the disease won’t spread further on the plant. Besides, ever since the first land plants evolved, quickly followed by plant diseases out to take advantage of them, that is, about 470 million years ago, dead leaves both sick and healthy have decomposed and enriched the soil. So far at least, this natural cycle has not managed to destroy plant life on this planet.

I must emphasize that, in spite of my recycling diseased leaves, I don’t have more disease problems in my plants than other gardeners. To be honest, I rarely have any, although I don’t think that has much to do with what I compost or don’t compost, but perhaps from a better choice of plants and my habit of pulling out plants that don’t like my conditions. Even my tomatoes are largely disease-free: hard to believe, I know, but true. And tomatoes get more than their fair share of my home-made compost.

For me, the subject is therefore closed: diseased leaves belong in the compost, period. Throwing them away is simply wasteful.

Long-Ago Radio Show

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If it’s green or once was green, you can compost it. That’s my opinion! Photo: SuSanA Secretariat, Wikimedia Commons

By pure coincidence, while I was driving in the United States a number of years ago flipping channels on the radio, I picked up a gardening show with several distinguished guests, including Lee Reich, a renowned organic gardening guru, and Mike McGrath who was, I believe, editor of Organic Gardening magazine at the time (I can’t remember who the third guest was: sorry!). Someone phoned in about whether he should compost diseased leaves and they all seemed in perfect agreement. Sure, you should compost diseased leaves. The consensus seemed to be that all vegetable waste belongs in the compost, healthy or not!

Reich made me laugh by claiming that even puts his old jeans in the compost, but it takes about two years for them to decompose. (I wear mine until they get so thin and full of holes they really aren’t decent any more: apparently my body is a working composter!)

What About You?

What will you do? Sort fall leaves into two heaps: diseased ones you won’t compost and healthy ones that you will? It’s up to you to decide, but the “all plant materials in the compost” method requires much less effort!20171008A Cephas, WC

Why Is It We Plant Spring Bulbs in the Fall?


20171007AHave you ever wondered why we plant spring-flowering bulbs in the fall? We’ve been doing this for so many generations that this now appears quite normal, but in fact we don’t plant bulbs then because we have to, but because it’s more convenient for the merchants to sell them to us in the fall.

Let me explain.

History of a Delayed Planting


From the bulb’s point of view, the best time to move or divide them would be as soon when go dormant, that is in late spring or early summer. Photo:

Logically speaking, the ideal time to plant bulbs of tulips, daffodils, hyacinths, crocuses and other spring-flowering bulbs would be in late spring or early summer when their foliage turns yellow and they go dormant. That way, the gardener knows exactly where to find them in the garden and digging them up is therefore easy. Just divide them and replant them, it’s that simple. There is absolutely no reason to delay their planting until fall. Remaining dormant under the soil in the summer is part of their growth cycle. They then start growing again when temperatures drop in the fall.

If, while gardening, you accidentally dig up bulbs—and that certainly happens often enough! —, most gardeners know enough to replant them immediately… and that is precisely what you should do.

However, if you want to sell spring-flowering bulbs, a late spring planting season is not at all convenient. They would have to be dug up, cleaned, checked for insects, diseases and blemishes, sorted by size, packed, shipped and ready for sale in just a few weeks. Even then, they’d have to compete for your attention with all the beautiful annual and perennial plants already in bloom that fill garden centers at the same season.

That’s why Dutch growers, who supply more than 75% of the hardy bulbs sold around the world, have learned that if they keep the bulbs in warehouses under strictly controlled temperatures and humidity, mimicking the conditions found underground, they can delay planting—and therefore sales—until fall.


Bulb growers allow themselves an entire summer to prepare spring bulbs for sale.

This gives them all summer to harvest, clean, sort, pack, etc. And it means they can take advantage of inexpensive means of transportation, such as container ships, to deliver the bulbs. There’s no need to rush! If even if bulbs dug in June don’t reach local stores until September, the usual scenario, that gives most gardeners over two months to plant them, something you’ll want to do before the soil freezes.

Soil Temperatures Not a Factor

It’s amusing to hear so-called experts insist on the importance of waiting until the soil cools down in the fall before you plant your bulbs. You often hear temperatures like 50 or 60° F (10 or 15° C) bandied about, but hardy bulbs from previous years, already in the ground, are going through whatever temperatures Mother Nature throws at them and still do fine.


No need to check temperatures: just go ahead and plant!

I imagine a poor gardener going out every day with a meat thermometer to check the temperature of the soil, waiting for the right moment before planting his bulbs. Yet soil temperature is just not an important factor in planting bulbs: they were designed by nature to be underground, no matter how hot the soil gets! Some grow in soil that becomes baking hot in summer, yet they thrive.

As a result, there is simply no need to take soil temperatures into account when planting your bulbs. Just plant the bulbs even if the soil is still warm and let Mother Nature cool the soil down as fall progresses.

So When Should You Plant Bulbs?

It’s always best to plant bulbs a few weeks before the soil starts to freeze, as hardy bulbs need to start producing their roots in the fall. You don’t want the ground freezing to any great depth before they’re well rooted. In most climates, that means any time between late April/early June (the beginning of the bulbs’ dormancy, depending on the variety and climate) and mid-November.

(There are a few bulbs that should be planted as soon as they arrive in stores: read more about them in the article 6 Bulbs to Plant Without Delay.)

So there you go! There is actually a vast window of opportunity—over half a year!—for you to plant spring-flowering bulbs, but the reality is that they only come on sale in September in most areas, so plant them then or wait a month or two: it really doesn’t matter, as you long as get them into the ground before it freezes. And just leave bulbs of previous years in the ground year after year: it’s their natural environment and that’s where they do best!

In Case of Early Frost

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Don’t let frost get your tomatoes! Here are some suggestions about what to do in the case of an early frost. Photo: pxhere

Most readers of this blog, which is essentially written with Northern gardeners in mind, will at some point in this fall see a first frost. Sometimes it occurs in a timely matter. Depending on where you live, the first frost is “expected” in September, October, November or even December. Since most of us plan ahead and prepare our gardens for that event, we’ve often completed our preparations for winter before that first frost occurs. Other years, though, frost occurs suddenly, weeks or even months before it should theoretically occur. That’s what we call an early frost.

In our grandparents’ time, gardeners were inevitably caught unawares by early frosts. These days, however, with weather information services widely available, there’ll usually be a frost alert: a day or at least a few hours of advance warning.

So, the media is announcing frost tonight, but your garden really isn’t ready. What should you, as a gardener, do?



Here are a few suggestions:

  1. Bring frost sensitive plants indoors. This would include any houseplants that have spent the summer outside.
  2. Also bring in cuttings of any annuals you want to overwinter indoors (coleus, geraniums, fuchsias, begonias, etc.).
  3. Harvest fruiting vegetables such as tomatoes, eggplants, squash, cucumbers, beans, etc. or…
  4. Cover the plants with a cloth, a blanket or newspaper, preferably using a few stakes as a support so the cover doesn’t squash the plants or …
  5. Turn the sprinkler on them before you go to bed: water flowing over the leaves will help keep the foliage from freezing.
  6. Apply the same treatments to frost sensitive leaf vegetables, like lettuce, Swiss chard and celery and annual flowers like begonias and impatiens.

Don’t panic about the following plants, though: they can handle an early frost.

  1. Summer bulbs (cannas, tuberous begonias, dahlias, etc.): the first frost may destroy foliage, but won’t penetrate the bulb. Do dig them up and bring them in before the ground freezes solid, though.
  2. Root vegetables (carrots, beets, turnips, rutabagas, etc.) are protected from frost just by being underground. Again, just make sure you dig them up and bring them indoors before the ground freezes.
  3. Some vegetables actually taste better after a frost or two, as a light freeze brings out their sweetness. This group includes cabbage, kale, Brussels sprouts, Jerusalem artichokes, leeks and parsnips.
  4. Spinach is very resistant to even severe frosts and needs no special frost protection. In fact, you can still sow spinach if you feel the ground won’t freeze solid in your area for another 6 weeks or more.
  5. Hardy plants (trees, shrubs, conifers, perennials, vines, etc.) are designed by Mother Nature to take a few degrees of early frost. At worst, they’ll be a bit of tip damage on leaves that, in most cases, will be dropping off soon anyway.

When you garden, follow the rule so familiar to boy scouts and always be prepared!

Time to Clean Up Red Ball Traps

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By the end of the season, a red ball trap can be nearly covered with apple flies! Photo:

I don’t know about you, but my apple trees are “decorated” with red ball traps covered with Tanglefoot (a non-drying glue sold in garden centers) from the time the tree stops blooming until about the time I start to harvest my apples.

I put them up to catch apple maggots (Rhagoletis pomonella)the so-called “worm” that bores holes in apple fruits, rendering them almost unusable—before they can do any damage. But by fall they’re no longer useful: the female moth that will lay next season’s maggot eggs is now pupating in the soil below your apple trees and won’t be harmful again until early next summer, leaving you with sticky red balls covered in dead flies. Yuck!

I supposed less environmentally aware gardeners probably just toss their traps into the garbage and buy or make more the following spring. However, I feel the need to do my ecological duty and recycle them. Indeed, they can be used over and over again and last for years. But that means you have the icky task of cleaning them in the fall.

Getting to Work


Putty knife. Photo:

So, set up a cleaning spot by covering a table—I prefer to work outdoors on one of those sunny, warm fall days—in newspapers, cardboard or a sheet of plastic—, get out a putty knife or table knife and put on some disposable latex or plastic gloves. Put on your earphones too and tune in to your favorite radio station or podcast. It’s time to get to work!

Holding the trap by its stem, carefully scrape it with the knife, cleaning the blade regularly with a paper towel or old cloth. When the insects and most of the glue have been removed, work baby oil or mineral spirits (an organic solvent also called white spirit or petroleum spirits) into the remaining glue, then wipe off what’s left with another cloth or paper towel.

When the trap surface is clean, dry it off and store it until next year. Clean the putty knife and put it away as well.

It’s a yucky job, but doesn’t take that long … and somebody’s got to do it!20171005A ?

Gardens of Light: Spectacular!


Yes, believe it or not, this full-sized sculpture illuminated from within is considered a lantern!*

I just visited the Gardens of Light show at the Montreal Botanical Garden and it’s absolutely spectacular!

Every year in September and October, the MBG lights up at night and offers extra opening hours in the evening so visitors can take full advantage of it.

A Short History


A few strands of Chinese lanterns at the entrance recall the first version of the Festival of Lights 25 years ago.

This colorful show began 25 years ago when the MBG imported hundreds of lanterns from China to light up their newly opened Chinese Garden. At the time, it was called “The Magic of Lanterns” and the lanterns were simply commercial ones, like those you could see anywhere in China. There was one single sculpture illuminated from within, all in yellow.

The exhibition has grown considerably since then, and now also includes the Japanese Garden and the First Nations Garden. This year’s “lanterns” are nothing like typical Chinese lanterns, but rather multicolored sculptures illuminated from the inside. This year includes the largest lantern sculpture ever presented at the MBG: a giant Chinese dragon that seems to rise from the waters of the garden’s main pond.

Visiting Garden by Garden

The show starts with the most spectacular part: the Chinese Garden.

This vast garden, freshly reopened after two years of renovation, is in itself breathtaking enough and certainly worth visiting during the day, but at night? Well, words simply fail me! You’ll be bowled over.


The dragon seems to dance on the water of the main pond.

This year, the theme is the Chinese dragon, the symbol of China, shown as an enormous illuminated sculpture that emerges from the main pond with its long undulating tail covered in blue scales. Chinese legend has it that the dragon lives in the heart of the oceans and clouds and is both beneficial and dangerous.


One of the dragon’s nine sons.

This year, the dragon is accompanied by its nine sons, each more colorful than the previous one. Around them dance red-crowned cranes, symbolizing the long friendship between twin cities Montreal and Shanghai. The effect is breathtaking!

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The Sacred Tree in one of its color permutations. Claude Lafond, Espace pour la vie

This is the first time the First Nations Garden has been included in Gardens of Light event. It features the Sacred Tree, a giant poplar illuminated by changing light projections that evoke the seasons and the perpetual transformations of nature. In this garden, a soundtrack lets us feel the heartbeats of Mother Earth and hear the crackle of fire as well as bursts of thunder.


A wall of the Japanese Pavilion serves as a screen to project images of autumn in Japan.

Don’t expect such brilliant color in the Japanese Garden. The lighting is softer and reveals the colors and textures of the plants while emphasizing the elegance of the pavilions and the garden’s natural harmony. It’s an invitation to slow down and enjoy the changing colors.

When You Visit


The Chinese dragon during the day.

Ideally, you’d arrive at the Montreal Botanical Garden during the day so you can see the three gardens during the daylight, then to go back in the evening, when it’s dark, for the light show. That’s what I did and it’s amazing how the gardens change completely when they are illuminated: it’s like visiting three entirely different gardens!

Pumpkins to Come


Photo: Espace pour la vie

If you can wait a few more days before visiting, there’ll be a second show at the Montreal Botanical Garden this fall: the Great Pumpkin Ball in the main greenhouse. It will run from October 6 to 31. It too is repeated yearly, just before Halloween


This year’s Gardens of Light show opened September 8, 2017, and will end on October 31, 2017. If you can’t make it this year, don’t worry. The MBG is already hard at work preparing next year’s show! Expect pretty much the same dates, so you can already book “travel to Montreal to see Gardens of Light show” on your agenda!

The Montreal Botanical Garden normally closes as dusk, but, during the show, ticket sales are extended until 9 pm, even 10 pm on Fridays and Saturdays as well as on Sunday, October 8th. You can stay for an hour after ticket sales end.

There is no special rate for the Gardens of Light event: it’s included in the usual individual rate. You’ll find this year’s rates by clicking here.

The Montreal Botanical Garden is located at 4101 Rue Sherbrooke East in Montreal, Quebec, Canada. There is ample parking on the site and a subway station (Pie IX) nearby.

Enjoy your visit!

*Unless otherwise indicated, all photos are mine, but, of course, feel free to share them. Just credit