The Caumsett Foundation

Sheet Mulching & Solarization

Long Island Community Foundation Grant 2021

This demonstration site shows two easy methods of converting lawn to garden space: Sheet Mulching and Solarization.

What is sheet mulching?

Sheet mulching uses cardboard and mulch to smother the grass and weeds below, allowing you to start your garden relatively weed-free. Any weeds that do manage to make it through will be much easier to remove. When is a good time of year to start this method? Start this project in the late summer or early fall for winter seeding or spring planting. Steps Cut the grass as short as possible, then cover it with a layer of cardboard or a thick layer of newspaper. Make sure the pieces overlap to keep sunlight from reaching the soil. Thoroughly wet the cardboard to help it break down. Cover with at least 4 inches of mulch or compost. There are 5 to 6 inches of mulch at the Caumsett demonstration site.

What is solarization?

Solarization is the process of placing a clear sheet of plastic over a lawn to heat up the soil underneath. The plastic traps heat and moisture which encourages seed germination and plant growth. The solarization process eventually kills the vegetation underneath.


  1. Clear plastic (2-6 mil) is sufficient for solarization.
  2. Mow the grass as short as possible before adding the plastic sheet.
  3. Moisture is a key ingredient for weed seed germination, so watering before installing the plastic sheet will improve performance. Water until the soil is moist down to about 12 inches before covering. The process typically takes around 2 to 3 weeks during hot summer months.

The process is complete when the vegetation underneath the tarp is dead. Tarps blow away easily and need to be held down. For solarization, it’s best to bury the edges to form a tight seal. If this is not possible, you can use landscape staples to hold the edges down, but take care to avoid tearing the plastic.You can weigh down the tarp with bricks or sandbags on the corners for extra support, especially in very windy areas.

What’s being planted?

Both garden spaces will be seeded with common milkweed seeds in November and evaluated in the Spring to see if either method was more productive for seed germination.