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.

Here are the key steps for solarizing soils:

1. Generally best to star during the hottest months of the year (June or July)

2. Cultivate the soil thoroughly and smooth out the surface so that the plastic will come in uniform contact with the soil.

3. Water the soil well. Moisture helps activate growth and conducts the heat deeper into the soil.

4. Spread the clear plastic over the area and weigh down the edges and seams with soil to prevent air from circulating under the plastic. For most situations, 3 or 4 mil plastic will hold up best over time.

5. Leave the plastic on for at least 4 to 6 weeks.

6. Remove the plastic after about 6 weeks since it will start to become brittle with exposure to ultraviolet light and become difficult to clean up.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.


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