Mulching Tomatoes with Straw
118 degrees on bare soil when air temperature is 91 degrees—that's what your roots are dealing with
A thick layer of straw around your tomato plants can drop soil temperature by 40 degrees. That's the difference between roots surviving and roots dying in summer heat.
What Is Mulching?
Mulching is adding 3-5 inches of coarse material—I use straw—on the ground around your tomato plants. Works for backyard soil and raised beds.
Why It Matters in Hot Weather
Surface temperature of ground soil and cement can be 20-30 degrees warmer than air temperature. On a 91-degree day, the soil around your plant hits 118 degrees. Tomatoes like warm weather but not hot weather.
A thick layer of straw keeps soil temperature closer to air temperature—sometimes even cooler.
The Temperature Difference
Same day, same time, same 91-degree air temperature:
Bare soil: 118 degrees
Under straw: 80 degrees
That's a 38-degree difference. That's what keeps your roots alive.
Same day, same time—under 3-5 inches of straw, soil temperature stays around 80 degrees
How to Apply Straw Mulch
Buy a bale of straw. When you pop it open, you'll notice 3-5 inch thick sheets break off easily. Lay these sheets around plants in a 4-5 foot radius. Fill gaps with loose straw.
Thick sheets of straw laid around plants, ready to fill in gaps
Gaps filled with loose straw—complete coverage around the plant
Use coarse mulch like straw so air and water get through easily.
What Straw Mulch Does
Keeps soil cooler - Prevents sun from directly hitting soil, which raises temperature and kills surface roots.
Prevents moisture evaporation - Tomato roots grow right to the surface under mulch. Without mulch, soil gets too hot, surface roots die, and moisture evaporates.
Blocks weeds - Weeds rob moisture and bring disease.
Fights pests and diseases - Very important. Mulch forms a 3-4 inch barrier between your plant and soil. Lots of pests and diseases come from soil, splashing up on plants when you water.
Mulching Containers
Mulch containers with straw for the same reasons. It keeps potting mix surface cooler and reduces evaporation.
End of Season Cleanup
By season's end, much of the straw will have decomposed. Rake up leftover straw and toss it in the trash—pests and disease-promoting organisms lie on top of the straw.
Next Steps
Complete hot weather protection guide →
Master watering in heat →
Learn the fundamentals →
Dave Freed / 
The Tomato Guy
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