Know About Heat-Stressed Veggies

Now that Colorado is finally moving into the hot days of summer, be aware of how warmer temps affect edibles – especially our No. 1 homegrown crop, tomatoes. While we often think tomatoes thrive on warm days, that’s not exactly the case.  According to the tomato growers at Jung, it takes about 5 weeks for a tomato flower to become a fully ripe fruit.  During the first 3 weeks it grows to full size and during the last 2 weeks, it ripens. Temps soaring above 90 degrees will slow down this process. What happens as temps rise?

  • At 85 degrees, pollination and fruit set will be affected.
  • At 95 degrees and above when night-time temps are higher than 75 degrees, flowers may fall off.
  • At 100 degrees and higher, plants are pushed into survival mode.  The red pigment in the skin may stop forming while the yellow and orange pigments continue.  When this happens, growers recommend picking tomatoes when they turn red and then allowing them to ripen indoors at cooler temps.

Once those really hot days have passed, it may take five more weeks to begin harvesting tomatoes again.  Fortunately, successive 100-degree days are rare along Colorado’s Front Range and at higher elevations. Cucumbers Multiple days of excessive heat can cause cucumbers to drop their blossoms or for developing fruit to become deformed and acquire a bitter flavor. When preparing cucumbers, cut off the stem end and peel off the skin as this will remove much of the bitterness.   Other edibles

  • Successive days in the 90s may cause squash, peppers, melons, pumpkins and beans to drop their blossoms and temporarily shut down.
  • Cool-season crops such as broccoli, cabbage, lettuce and spinach will bolt in the heat. Wait for cooler days to replant.

Other heat-related problems

  • Blossom end rot is common during hot weather.  You’ll often see it in tomatoes, peppers and squash.
  • Spider mites like to show up during hot, dry weather and one sign they are active is leaves that look stressed.   The go-to way to check for spider mites is to hold a sheet of white paper under the leaves and tap the plant. You may see the specs move (they are mites) and if you run your hand over the paper, you will see streaks on the paper. To control spider mites, consider applying an insecticidal soap according to label instructions.  Note if there are precautions that apply to edibles.

TLC for heat-stressed plants Allowing plants to dry out during a heat wave will stress them further.

  • Check soil moisture often and keep the soil uniformly moist to keep plants from wilting.
  • Apply mulch around the plants to keep the soil cool and to retain moisture.

The good news about hot, dry weather is that it deters fungal diseases such as powdery mildew on impatiens and edibles as well as Ascochyta blight in lawns – all of which have been a problems in some areas this season as a result of prolonged periods of precipitation.

Contact Designscapes Colorado at or 303.721.9003.


This entry was posted in Gardens, Residential, Lawn & Garden Care, Annuals & Perennials