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We have a rather small garden and would like to start growing some vegetables and herbs. We already reserved a part of our garden for this, but at the edge of this part there currently is a forsythia growing. It is about 1.5 meter high. My question is; would this cause any problems to our kitchen garden?

The main thing I'm concerned about is that the forsythia may excrete substances that may be toxic, or that it may draw away lots of water from the herbs and vegetables. I like the forsythia so I'd rather not clear it. I would relocate it, but since our garden is small there is hardly any room left to move it to.

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The biggest problem might be the amount of root in the ground from the plant, in terms of being able to dig and plant other things, but toxicity isn't a worry. Prune it after it flowers, you can be as severe as you like. Also consider how much shade it will cast (if any) on any food plants you're growing - you don't want those to be in shade most of the day.

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  • I saw many time forsythia cultivated as a fence. I'd like it very much, because the forsythia blooms very early in spring. So pruning can be done much earlier that garden plants need of the sun. – violadaprile Apr 16 '13 at 17:26
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    Depends how fond you are of the flowers, though, Viola - pruning to get good flowering is somewhat different from pruning as a hedge, although in my experience, it tends to flower regardless, just not quite so much. – Bamboo Apr 17 '13 at 12:09
  • Very true. But i love them anyway :) – violadaprile Apr 17 '13 at 13:13
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I have a vegetable garden with forsythia growing within a foot or so of the edge of the garden on the west side. I have grown all kinds of vegetables in this garden for the past 15 years with no issue - at least not related to the forsythia :) They provide a very pretty backdrop to the garden.

You just have to keep the forsythia cut back so it don't shade the garden too much, and also so that no low-hanging branches take root in your garden. I take advantage of the shade by growing lettuce, spinach and other plants that like a little shade in the row closest to the forsythia so they get some relief from the hot afternoon sun.

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I don't think forsythia will cause any toxicity problems. The worst case that I see is that you will disturb its roots while you are digging for your vegetables. I might dig carefully right near the forsythia and plant perennial herbs that will tolerate partial shade (assuming the forsythia cast shade over that area). Alternatively you could build a raised bed there and plant relatively shallow-rooted vegetables that will be helped by shade from summer sun like lettuce or spinach.

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This article indicates that Forsythia has alleopathic effects on these plants:

  • Black Cherry
  • Goldenrod
  • Kentucky bluegrass
  • Sugar Maple
  • Tulip Poplar

I also see an an article saying kentucky bluegrass inhibits forsythia.

It seems to be very competitive in the plant kingdom. The results of these studies are also based on particular soil types and climate and they don't indicate how much growth is inhibited.

I have the same opinion as @bstpierre and @Bamboo that as long as the forsythia is not shading the garden and it's pruned back it should not be a problem for vegetables.

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This might help you find more information. The toxicity you're referring to when one plant secretes a substance that is toxic to other plants is called "allelopathy".

I did a quick search for allelopthic forsythia and it turns out it is. This page lists some info and some of the plants that won't work well with forsythia. http://gardening.about.com/od/gardenproblems/a/What-Is-Allelopathy.htm

It's not a complete list so you might want to look for specific plants you want to add.

Update: Out of curiosity I did some specific searches trying to find any info regarding how forsythia might impact vegetables and I can't find much. It makes sense. Landscape plants are usually not planted with vegetable crops so it would be unlikely for a researcher to have the incentive to look into it.

You may want to look into the families of plants that forsythia can deter and compare it to the family of vegetables you plan to plant.

For example goldenrod is affected by forsythia. It is in the aseraceae family. So is lettuce, sunflower, artichokes and marigold (not edible but good companion plant).

Black cherry is in the rosaceae family as are strawberries, apples, plums and peaches.

Now I'm curious. Hope you can post an update on how things went.

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About forsythia allelopathy: Within the last six months, I removed some very old (20+ years) and strong thickets of forsythia. I treated the stumps with Triclopyr, which is claimed by all sources I have seen, to have no soil activity. One thicket stayed gone, another suckered from the stumps. I replanted with several small shrubs. Two little Calycantha plants died outright in the area with live forsythia. In the area with no growth, but with stumps still in the ground, two freshly planted hydrangeas immediately started to crash. I popped them out and potted them in commercial potting soil, and they are recovering nicely. In the same area, a Dianthus died slowly over the summer, and a Fatsia has been struggling for two years. I just repotted the poor Fatsia and hope I have saved it. I realize that this is completely anecdotal, not scientific, but I'm going with forsythia allelopathy being a legit complaint. I assume that the toxins are leaching from the old root wood still in the ground. It will be interesting to see how long it takes these toxins to clear out, esp as the soil is horrible red clay.

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  • Could you clarify if you believe the toxins to be produced by the forsythia itself (allelopathic) or are residual from the Triclopyr application (persistent)? – That Idiot Aug 12 '15 at 14:51

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