If you have the time, one
of the best ways to prepare a site for new beds and
borders is to "solarize" it. What this boils down to is
"baking" the soil in place. If done properly,
the process will result in a soil temperature of 140
degrees near the surface and up to 100 degrees down
to a depth of 18 inches. This is hot enough to kill
most insects, weed seeds and certain fungal diseases
such as Fusarium and Verticllium wilt
and Rhizoctonia root root fungi. Nematodes
may be at least partially controlled at these
temperatures too.
All you need to do is remove
all the vegetation from the surface of the soil and then
cover the entire area with clear plastic sheeting. Be
sure to weigh it down with some rocks so the wind
doesn't blow it away. Then, sit back and let nature and
the sun do their job.
To be effective, you will
probably need to keep the plastic over the ground for a
summer season. This will allow the hot sun to bake the
ground and raise the temperatures to the point where it
will be able to kill dormant seeds, roots of perennial
plants, insects and their eggs and disease organisms
such as fungal spores and bacteria.
Be aware that perennial
plants trapped beneath the plastic will grow like crazy
in the hot, moist environment...at least for a while.
Eventually, the heat will be too much for them and they
will die but they may push up on the plastic before that
happens.