Mulch tomatos with straw during hot weather

What is mulching?

In your regular backyard soil/raised beds, mulching is adding a three, four or even five inches deep of a coarse compost type mulch on the ground soil around your tomato plants. I use straw.

Why is mulching with a thick layer of straw extremely important during hot weather? 

Mulching prevents soil around your tomato plant from getting too hot in mid-summer. 

The temperature of the surface of ground soil and cement around your tomato plant can be 20-30 degrees warmer than the outside air temperature. 

On this day, the outside air temperature at 3 p.m. was 91 degrees. The temperature around the tomato plant at 3 p.m. was about 118 degrees. Tomatoes like warm weather but not hot weather. A thick layer of straw keeps the temperature of the soil under the straw closer to the outside air temperature.

Buy a bale of straw and spread three, four or five inches deep about four to five feet around your tomatoes. When you pop open the bail of straw, you will notice three, four or five inch thick sheets easily break off the bail. Lay these thick sheets around the plants as you see in the picture above. Then fill in gaps with the loose straw as you see in the picture below.

Mulch needs to be rather coarse. I use straw, so the air and water get through easily.

On this same day when the outside air temperature at 3 p.m. was 91 degrees and the surface temperature of the soil around the tomato plant at 3 p.m. was about 118 degrees. The following picture was taken that same day at the same time. 

The temperature of the soil under the layer of straw was about 80 degrees, almost 40 degrees cooler. Hot weather is the enemy of tomatoes. The layer of straw keeps your soil around your plant cooler. Mulching brings that temperature of the soil back down at or lower than the outside air temperature.

The following picture was taken the same day at the same time. The temperature of the soil under the layer of straw was about 80 degrees … almost 40 degrees cooler. Hot weather is the enemy of tomatoes. The layer of straw keeps your soil around your plant cooler. Mulching brings that temperature of the soil back down at or lower than the outside air temperature.

Mulching with a thick layer of straw:

• Keeps the soil under the straw cooler. Preventing the sun from directly hitting the soil around the plant which raises the soil temperature, kills surface roots of tomato plants.
• Prevents moisture from evaporating. The tomato roots will grow right to the surface under the mulch. Without mulch the soil becomes too hot, surface roots die and moisture in the soil evaporates.  
• Prevents weeds from coming up. Weeds rob moisture, weeds bring disease
• Fights pests and diseases: Very, very important. Mulching forms a three or four inch barrier between your plant and the soil. Lots of pests and diseases come from the soil, lying on the soil and splashing up on your plant when you water, etc.

Mulching with straw in containers

Mulch containers with straw for much the same reasons above. It keeps the surface of potting mix cooler and reduces evaporation.

By the end of the season, much straw will have decomposed. The leftover straw, I rake up and toss in the trash as many pests and disease promoting organisms lie on top the straw.

Feel free to share these tips with your gardening friends and communities. The more we share, the more we grow!

Dave Freed /  the Tomato Guy