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Companion Planting Clarification

Please can anyone tell me if companion planting advice applies only to plants in the same soil or whether it can sometimes apply to plants next to each other but in different pots. I have several pots of various herbs, including dill, situated very close to my veg trug which I am now reluctant to plant up as, it seems there may be some conflict - dill particularly being a bad boy!  I am a novice to both companion planting and veg trugging. 


  • Womble54Womble54 Posts: 348
    I’m no expert but there are a range of reasons why plants make good or bad companions. Some are related to being in the same soil, liking similar conditions or competing for nutrients. Others are related to proximity, attracting pollinators, deterring pests. Sometimes it’s structural reasons like providing shade and support.

    With Dill I think they can stunt the growth of some root crops if in the same soil, or can cross pollinate with some plants, so avoid being close together even if in pots.

    Hope that helps.
  • Yes it does, very much, thank you  I have trawled through many charts but nowhere does it actually distinguish between the plants being in the same soil (except for the nitrogen fixing of beans) or just in close proximity.  I think I'll play it safe and plant the Dill in the front garden as I plan to grow tomatoes and beans in my veg trug and note your valid comments on cross pollination. Cheers for that.
  • NollieNollie Posts: 7,512
    When plants are listed as bad companions, it usually is a soil-based allelopathic reaction (one plant exhudes allepathic chemicals that inhibits the growth of another, although there are a few that exhude chemicals from the leaves as well, but this normally affects soil too, as the leaves drop around the plant, e.g. Walnuts). Good companions can be so because they have a positive allelopathic effect, simply because they don’t compete, because they provide shade or they smell masks pests. I’m fairly sure that close proximity/the smell alone of one plant can’t have a negative effect on another, except perhaps if it deters beneficial pollinators for that plant, but I’ve never heard of that. 

    Tomato companions:
    You mentioned in your earlier post that you thought sunflowers, dwarf french beans and tomatoes shouldn't be grown together, but I know that beans and tomatoes together are fine, in fact they are often listed as good companions. I’m not aware of sunflowers having a measurable allelopathic effect on toms, but is probably not the best combination because they are both very hungry plants and maybe its competition for nutrients there. Fennel, and to a lesser extent dill inhibit tomatoes and should be kept well away. Basil is the best companion herb to grow with toms.

    While there are measurable allelopathic effects of companion planting, there is also a lot of guff out there so it can be very confusing and contradictory. There was a discussion about companion planting (in the context of crop rotation) recently in the Fruit and Veg forum that you may find interesting:

    Hope that helps.
    Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
  • Thank you Nollie, that’s very reassuring and you are right, there is a lot of confusing, contradictory guff out there.  My sunflowers will be in separate tubs anyway, either side of the trug  that the tumbling tomatoes will be in, but I’m not worried about them being close, after your comments. I did go the link you sent. I must admit I hadn’t thought about crop rotation for next year. That’s something I’ll have to study later. Thank you for your time 
  • raisingirlraisingirl Posts: 7,080
    The specific cross pollination problem with dill is to fennel. Grown near each other they affect the flavour of both, producing something called fendil which doesn't taste as nice as either should.

    Most plants from different plant groups don t readily cross with one another so dill won't cross with tomatoes afaik.

    It's quite a complex issue, isn't it? I find it fascinating but there is still a lot I'm learning 
    Gardening on the edge of Exmoor, in Devon

    “It's still magic even if you know how it's done.” 
  • NollieNollie Posts: 7,512
    You are welcome, OLA, it is difficult sorting the wheat from the chaff. Rotation planning is another headache that took me years to get sort of right according to what I want to grow/eat.

    If someone says don’t plant x with y I want to know why,  how it works or doesn’t work and what the chemical interaction is. The science just isn’t there for many things tho, sometimes its just decades of experience from growers saying if you plant x with y you get a poorer crop. Bob Flowerdew did some interesting experiments that indicated the veracity of some of the old folklore, so I tend to trust his judgment, but do wish he would back up his statements sometimes, because many things he does say are scientifically verifiable. Perhaps thats just me being a geek, although I think ‘curious and enquiring’ sounds better  :)
    Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
  • Raisingirl, yes - fascinating but complex and I think you can read too much sometimes. I did, for hours, until my head was mashed which was when I decided to join this forum. Wish I had done years ago tbh for all my other gardening queries. 
    Nollie, geek is good. It takes the legwork pressure off science lightweights like me!!!
  • BLTBLT Posts: 525
    I have read all of the above posts with interest and I too wonder about cross pollination. But Bees will be Bees and they probably prefer some flowering species to others..   
      But Re Companion planting   I always thought that if you planted Onions next to carrots each protected the other from onion and carrot fly.

    Also a well known companion planting is thousands of years old and is the native american way of cultivation.   Corn and beans and squash are grown together. In that the tall corn provide a support for the beans and the squash provides ground cover to suppress the weeds and stop the ground from dtyung out... It has worked for them for centuries.  Just a thought... :D
  • NollieNollie Posts: 7,512
    BLT, don’t worry about cross-pollination, apart from the dill/fennel already mentioned. Most vegetables are grown as annuals, and even of they could/did cross-pollinate across species this would only apply to new seedlings if you left things to self-seed.

    Yes you are right, onions and carrots are good companions.

    Again, you are right about corn, climbing beans and squash, a classic combination, although you need very good soil and a lot of water to grow these three together. I grow my squash (well, courgettes, both curcubits) in the shade of corn. I grow peas and broad beans together in a different area, because they are both legumes that like the same conditions. Broad beans do not need the same kind of support as climbing beans. Also, the broad bean crop is harvested before the corn really gets going!
    Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
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