On Tue, 30 Dec 2003 17:56:55 GMT, Janet Baraclough
wrote:

The message
from Frogleg contains these words:

"Companion planting" usually touts the benefits of
attracting/discouraging insects, but IMHO has mostly to do with with
plants that enjoy similar conditions.

There's more to it than that, concerning the chemicals in plants. Onion
family benefit some plants (like roses) but discourage others. Mexican
marigolds supposedly repel couch grass.

Odd. Marigolds are recommended here to repel soil nematodes. Never
heard of it as a weed repellent. And we *do* have "couch grass" under
several names. Garlic is supposed to benefit roses in some way. But
then, garlic is recommended for almost anything. :-) Perhaps a lot of
this is owing to a strong scent or vivid coloring appearing unusually
powerful. It would be very interesting to see studies of "companion
planting" under controlled conditions. I find it interesting (and
discouraging) that we have far more evidence of plants that *attract*
certain pests. The caterpillar of the lovely Swallowtail butterfly is
*mad* for dill and parsley. And carrots tops, if it can't find my
parsley.