What plants do not do well together?

I remember reading somewhere that onions or garlic planted too close to some plants (peas, I think?) may not be good. Does anyone know of any bad combinations?
CIndy

Dill and Fennel shouldn't be grown together as the fennel has an inhibiting effect on the dill. Some plants have roots which are poisonous to other plants, Rhodos are a good example as is Yew, this enables them to colonise a whole area. Similarly marigolds (Tagates)are poisonous to couch grass.

Black walnuts to everything.

what plants are poisoned by rhododendrums?

Cindy, you are right..it is peas and all legumes that onions and garlic affect. I have a great book by Rodale called 'Companion Planting'. It gives a really good listing of things not to plant by each other.
Debi, the book shows nothing about rhododendrums having a toxic affect on other plants. I hope that is good news for you :)

debi_z and justmelisa take a look at this page about rhodo's in the uk:

http://www.offwell.free-online.co.uk/rhododen.htm

lil

wow lilith! that is something!! thanks! Lisa

im certainly gonna think twice about getting one ...

lil

Well, I'm glad I never really liked rhododendrons anyway!

I garden near the New Forest in England and whole areas are taken over by Rhodos, Mount Snowdon in Wales has similar problems.

Epilobium (rosebay willow herb) was grown as a garden plant at one time in Victorian gardens. It was very popular, it is now an incredibly invasive weed. Buyer Beware!