"Frank Martin" wrote in message ...
Are some plants better planted in a group of their fellows than just singly?
My grandmother says some plants are like flocks of birds and do better in a
group. Does anyone know about this?

One way that a group of plant of the same species growing in close
proximity may interact in a mutually beneficial way is root grafts.
Tree roots from different individuals often naturally graft together,
which allows trees to exchange water, mineral nutrients and organic
compounds. A tree that is experiencing a shortage of these substances
can get them from its neighbors. Root grafts can explain why a tree
stump can remain alive for years after the trunk was cut down. Root
grafts might also help young trees to survive in the dense shade of
older trees and can increase anchorage.

One drawback to root grafts is that they may facilitate disease
transfer. At the Penn State University main campus, they used to
trench around any American elm suffering from Dutch elm disease so the
disease would not be transferred to healthy trees via root grafts.

There is a subdiscipline of plant ecology termed phytosociology, which
studies the interelationships among plants growing in the same area:
http://www.yale.edu/fes519b/saltonstall/page3.htm

Some scientific articles on root grafts a

Basnet K., F. Scatena, G. Likens and A. Lugo 1993. Ecological
consequences of root grafting in tabonuco (Dacryodes excelsa) trees in
the Luquillo Experimental Forest, Puerto Rico Biotropica 25: 28-35.

Bormann, F.H. and B.F. Graham Jr. 1959. The occurance of natural root
grafting in eastern white pine, Pinus strobus L., and its ecological
implications. Ecology 40: 677-691.

Graham, B.F. Jr, and F.H. Bormann 1966. Natural root grafts The
Botanical Review 32:255-292.

Keeley, J.E. 1988. Population variation in root grafting and a
hypothesis Oikos 52: 364-366.

Kuntz, J.E. and A.J. Riker. 1955. The use of radioactive isotopes to
ascertain the role of root grafting in the translocation of water,
nutrients, and disease-inducing organisms. Int. Cong. Peaceful Uses
Atomic Energy (Geneva) Proc. 12: 144-148.

Will, G.M. 1966. Root growth and dry-matter production in a
high-producing stand of Pinus radiata. N.Z. Forest Serv. Research Note
44.