Will oak leaves stunt plant growth?

pbsjones(Sunset 14/USDA 9)August 8, 2005

I've had a pretty disappointing garden the last couple of years, and I'm beginning to wonder if my beautiful live oak has something to do with it. The garden is located outside the drip line; I don't use the leaves in my compost, because I like the way the tree self-mulches (not in front of the kids!) but some do fall in, anyway.

Year one, I planted tomatoes in the available soil with store-bought compost, plus a little bit of homemade compost from my previous house. Great results.

Year two, planted tomatoes in lasagna-style raised beds. Okay production. Thought maybe they hadn't gotten enough water. Noticed a lot of roots from the oak had migrated into the yummy, rich soil.

Year three, planted in containers filled with potting soil and homemade compost to avoid the tree root problem, and because I wanted to see if it made watering any easier. Very disappointing results.

Year four, planted in the ground amended with homemade compost and got about three tomatoes.

This year, I've got my 'maters in containers, and I mulched two with oak leaves and two with pine needles. Guess which ones are doing poorly? Yup, the ones snuggled under the leaves.

Whaddaya think? Do oak trees do the same chemical thing that black walnuts do, with the juglone? And am I "poisoning" my tomatoes and compost by having the leaves around?

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No, oak leaves do not have juglone in them. In fact, I once heard Eliot Coleman say that everyone thinks oak leaves make the soil more acidic. But, in fact they just have the best ability to find nutrients in acidic soil which makes them great for tilling in your garden. Try tilling the leaves in the soil in the fall.

    Bookmark   August 8, 2005 at 11:09PM
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Using oak leaves as a mulch did not cause poor growth there is another reason. Oak leaves do contain large quantities of Tannic Acid, a natural preservative, but in over 30 years of using mostly shredded oak leaves both as a mulch and in my compost I have not see any plant growth stunted.
You need to look deeper for the reasons.

    Bookmark   August 9, 2005 at 7:17AM
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kjggames(z9/10, sunset16)


Are you planting tomatoes in the same spot over and over? Try crop rotation of at least 3 years per spot. Tomatoes one year, fallow one year, peas/beans one year, and so on and so forth. And yes, even if you amend the soil. Tomatoes, like many garden vegetables, are heavy feeders.

Also, how many plants are you planting? More is always better, no matter what the plant. If that one or two seeds you got to grow your one or two plants are duds, you are stuck. 6+ on the other hand, not only will you get a runt, but you'll get a super producer too. Finally, are you using the same tomatoes? There are different types of tomatoes, that produce their fruits differently (determinate vs. indeterminate).


    Bookmark   August 9, 2005 at 2:15PM
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I have planted my tomatoes in the same bed, along with Dahlias, for 4 years now and not only not see any problem with disease or stunted growth but have not seen a sign of a tomato hornworm. Years past I have had them. The soil is amended with compost at the end of each growing season and heavily mulched with leaves, mostly oak. In spite of some peoples thoughts I doubt that rotation will help much in the average home garden. Crop rotation is necessary when large fields are planted to the same crop but if the average home garden soil is amended with compost each year rotation should not be necessary.

    Bookmark   August 9, 2005 at 5:14PM
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rhizo_1 (North AL) zone 7

Not the oak leaves, but I would consider your potting mix, fertilizer practices and other inputs that you have control over.

    Bookmark   August 9, 2005 at 8:41PM
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pbsjones(Sunset 14/USDA 9)

Dang. Back to the drawing board then, I guess. Well, at least I know that the oak leaves are okay.

Thanks, guys!

    Bookmark   August 9, 2005 at 10:20PM
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kjggames(z9/10, sunset16)


I've never heard of home gardeners not rotating annual crops. Could you please point me toward a website or book so I can catch up on this?

Also, I was under the impression that the BIG FIELD guys, and not the home gardener,who are the ones not practicing crop rotation, and are instead using monoculture practices, not the other way around.

Further, I think you may be rotating your crops without knowing it...5 - 6 month growing season, 6 - 7 month fallow, 5 - 6 month growing season, 6 - 7 months fallow, and so on.

My ignorance is bliss,


    Bookmark   August 10, 2005 at 4:59PM
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Could your oak leaves or the leaf litter be contaminated with a virus or maybe nematodes? Sounds like it might be a disease of some sort. Anyone know of a virus that is common to both species?

The pattern you talk of suggests nematodes to me but that's easy to tell from the tomato roots. They would look like crinkly french fries instead of roots.

Maybe someone else knows more about diseases than I do can suggest something. In the mean time I would stick with the pine straw for sure :)

    Bookmark   August 10, 2005 at 5:35PM
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My perennial beds are never rotated and there are no diseases in them adn since it works well in perennial beds there is no reason why not rotating your vegetable crops would not work the same way, provided that you add compost and other organic matter annually. Of the several reasons to rotate crops is to help maintain soil fertility and reduce to possibilty of soil borne pests and diseases building up in the soil, monoculture does that if the soil is not properly cared for. The Natural Resources Conservation Service, a division of the USDA, tries very hard to encourage large farms to practise crop rotation and one those farms maintaining a good distance between where you planted corn last year and this year as well as a buffer crop between them is easy. Moving your sweet corn at least 300 feet often is not possible in the home garden and is not necessary if the soil is properly cared for. This link to ATTRA will give more information about crop rotation if you are interested in knowing more about that.

Here is a link that might be useful: Crop Rotation on the Organic farm

    Bookmark   August 11, 2005 at 4:06PM
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I thought I would add my 2 cents here. In the Fall when my veggies are done for the season I begin burying my kitchen waste. I dig a hole in the garden. I dump in the waste from the kitchen and cover it by making a new hole next to the first one. That way my hole is ready for the next bucket of scraps. I do this until I have the whole are done. My tomatoes are doing so well this year, that people are asking me why! lol Just thought I would offer this. I can't hurt and could help.


    Bookmark   August 17, 2005 at 8:36AM
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Tyrell(Zone 9, CA)


I would try using grass clippings mixed with the oak leaves, or by themselves. In all the charts of nutrient content I've seen, leaves always have about 1% nitrogen, Vs 4% for grass clippings. And while tomatoe don't need a lot of N, in fact too much can reduce fruit set, stunted plants could be a sign they aren't getting enough.

One question, and then some suggestions.
Why do you think that the oak roots growing in your garden are a problem? If you think they are stealing water from your plants, you could just water more. And if you worry they are stealing nutriens, just keep adding organic matter-like grass clippings, kitchen scraps, leaves, and crop residues at the end of the season- and there will be more than enough nutrients to go around.

If you do decide to keep growing in pots next year, some things that might help:

1. The above mentioned grass clippings. Pile it on as thick as will fit, but at least 3 inches. Don't let the clippings touch the stems of your plants, though, cause that could rot them. You can make small collars from yogurt cups to prevent that.

2. Potted plants need to be watered much more often than ones in the ground. And one potential problem is the water simply running down between the soil and the insides of the pot. (Soil shrinks when it dries and often creates a space here. You water, see some run out the bottom, and think you've soaked the soil. But the rootball is still bone dry!)
If you don't already have it, put something under the pots to catch water. That will collect the water that quickly runs through the soil, and then be slowly drawn up into the rootball by capillary action. That's the principle behind "self watering" pots.

3. Another problem with potted plants is the pots getting so hot they can cook roots touching them on the inside. If possible, put your pots where they'll get morning sun but afternoon shade. If there is no place you can do that, then wrap something like cardboard around the southwest sides of the pots, to keep the afternoon sun off them.

Plants, like animals, are complex organisms. There are often many factors to consider in getting the best out of them. This year is drawing to a close, but hopefully you'll have a much better year in '06?
Oh, I simply don't believe in crop rotation. I've grown my tomatoes in the same spot for close to 20 years, and grew them in another area for almost 15 before that, with no problems with "buildup of disease organisms." We are Never going to get rid of all disease organisms. So I think a much better approach is to try to establish "a balance of nature," so the "good guys and gals" can fight "the bad ones."

    Bookmark   August 23, 2005 at 9:53AM
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cochiseaz8(az 8)

I must disaggree with the folks who are pro (planting under oak trees) I may be totally out of line with those who have real oak, instead of live oak.. but in my experience, planting under live oak is a real crap shoot, as the soil is truly tannis , which is great for herbs, don't get me wrong!!! but is poison for tomatoes, peppers, sprouts, cabbage, basil, and most root crops. Yes , planting under and oak tree will maime, if not out-right kill your veggie garden. cochise

    Bookmark   August 29, 2005 at 10:58PM
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pbsjones(Sunset 14/USDA 9)

Thanks, everyone for your suggestions. I'm pretty sure I've figured it out.....No one laugh.... I just wasn't watering enough. Tyrell made a good point about the potting soil shrinking as it dries out, allowing the water to run out and not be absorbed. Even the faux drip system I made last year out of a piece of hose probably wasn't good enough, because of the hardness of my clay soil; it looked like the ground was soaked, but it probably only sank in an inch or so.

I was trying a little too hard to conserve, I guess. I pretty much doubled the amount of water I was giving to my veggies and flowers, and they took off -- how embarrassing! So, now, along with billows of sweet alyssum and some very happy salvia, I've got tomato plants with little baby tomatoes so late in the season that I don't think they'll be ripe by the time the cool weather comes. What a shame...I may end up having to fry them up green and gobble them down!

    Bookmark   September 25, 2005 at 11:53PM
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gaiaso(zone7 VA)

Message boards; What a great invention! Y'all got it all figured out back in '06. Years later here I am searching for info on putting leaves in the garden, as I have rather clay soil here in the piedmont of Virginia.

In addition to all the insights provided in the previous posts I found one more thing to factor in. At the Missouri Department of Conservation website, they talk about phenols that are released from oak leaves in the first months of decay, which inhibit sprouting and growth. I guess it's one way oak trees guard their territory.

I was thinking about spring mulching with oak leaves. I guess I just need to build another composting bin especially for leaves, and get some fresh straw.

Here is a link that might be useful: Autumn Leaves: Myth & Reality

    Bookmark   March 10, 2008 at 8:36AM
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The oak leaves are great mulch! You just don't want to mix/pile oak leaves on when you fist seed a bed as not only might they inhibit germination a bit but tender seedlings have trouble pushing through heavy mulch. Once the seedlings are up and big enough not to be buried, mulch away!!!!!!

Here is a link that might be useful: My Garden

    Bookmark   March 10, 2008 at 1:43PM
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That, tclynx, applies to any mulch material, not just Oak leaves. The article posted by gaiaso is really good even though it does perpetuate some myths in the article.

    Bookmark   March 11, 2008 at 7:59AM
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Have the tree's roots been allowed the remain in the garden area? They are very difficult to stop. When you cut them out next to your plantings they grow back quicker than your tomato and have gotten under your root zone as well.

Gardening next to a tree is difficult at best and mulching invites in the tree roots for years without abatement.

    Bookmark   March 11, 2008 at 8:47AM
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naw, the problem seems to be rotation, pests and disease will feed and reproduce on the same crop over and over, rest thatarea and plant a cover crop for aseason

    Bookmark   May 11, 2011 at 1:19AM
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My Uncle(at70) shredded a yard full of oak leaves & filled a 4X6X concrete block bed 8 inches deep with NOTHING, but the the shredded leaves. He did this in the Fall & planted Strawberries in the spring. When I went up to see him (zone 7)
his new plant where covered with BIG half ripe berries & young runner. I told him he was supposed to pinch off the berries & runners the first year.
He just grinned.
That was 3 or 4 year ago, I was up at his place last month. 12 months or so after he past & the plant looked great.
I would say you can not go wrong with them.
I never saw a nitrogen problem & he never fertilized them I am mulching tomatoes with the oak leaves this year, just like last year.
I think you are lucky to have oak leaves in any form.

    Bookmark   May 15, 2011 at 10:15PM
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Every 1% increase of organic matter increases the water holding capacity by 100%.
The above link, did not work for me.

Here is a link that might be useful: O.M. matters

    Bookmark   May 20, 2011 at 10:06PM
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Are you using grass clippings in your homemade compost?? The grass in your yard will carry any herbicides you put down right into the compost pile. The only thing i noticed in your original post was that you used some homemade compost in each progressively bad year.

    Bookmark   January 26, 2013 at 10:17AM
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Also, some oak leaves do contain tannins which '... are mainly physically located in the vacuoles or surface wax of plants. These storage sites keep tannins active against plant predators, but also keep some tannins from affecting plant metabolism while the plant tissue is alive; it is only after cell breakdown and death that the tannins are active in metabolic effects.' Meaning Tannins do have a physiological effect on the growth of plants. The good news is that 'the leaching of highly water soluble[8] tannins' into the soil will not last long since they will wash away with the rain.

Tannins are polyphenolic compounds found in some oak trees. I want to stress the 'some', and not say that all oaks have them. Plants, like every other living thing, will stop and start different metabolic processes depending on the environment. Some oak trees are allopathic, and some aren't. It all depends on the situation.


    Bookmark   January 26, 2013 at 10:25AM
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I recently learned that trillium like to be under oak trees with a high canopy. Also, blueberries like oak leaf mulch.

    Bookmark   May 17, 2014 at 6:01PM
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Well - with 4 huge pin oaks - I'm covered up with leaves. I've made a huge pile and was putting my kitchen scraps in the pile until I had a city of voles move in. So I stopped with the kitchen scraps, got a cat - & now I'm reading all this conflicting info. I don't shred the leaves & they do break down - this is so confusing.

    Bookmark   February 8, 2015 at 11:43PM
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