permaculture

[Jack Rowe <jackrowe@compuserve.com>]

Good points, Dan, when you wrote:

"Most vegetative propagation results in a root system that varies from that
of a plant propagated from seed... Adventitious roots don't seem to form a
tap root when the clover is transplanted."

And strong taproots are vital to drought-resistance in many plants. Many
arid-adapted plants, such as Tepary bean and alfalfa, use about as much
water as other plants but have amazing taproots which rapidly grow to great
depths. Tepary beans can follow a single rainfall as it drains downward
through the soil to produce a crop of viable seeds.

A Seeds of Texas board member has worked selecting seedlings of Tahitian
squash, Daylilies, corn, etc. by planting hundreds or thousands and then
letting 90% die in our Texas heat before assisting the survivors to produce
seed. Initial seedlings had a mix of root systems tending either primarily
toward fibrous- or tap-rooted systems. In soil which was well-drained and
permeable to several feet, the seedlings over several seasons shifted to
plants with consistently-strong tap-rooted root systems. After three
seasons of selection, the remaining squash plants were able to survive and
produce normal-size fruit during our long, hot, dry summers without
irrigation (5 months at 90-105F, 30-40C, average 45-50 day-droughts in the
95-105F, 35-40C range). In beds overlying dense clay subsoils where
taproots would suffer from lack of oxygen, the seedling roots remained
fibrous and shallow, and the plants were not able to adapt to the summers'
droughts. 

Jack Rowe