Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
The past several years have had periods of extreme heat that have caused fruit quality issues in tomatoes and peppers. Research has shown that high bed temperatures and the effects on root function have contributed to these problems.
One solution is to reduce bed temperatures by using white or reflective mulches. These can lower bed temperature by up to 20°F. This in turn can increase root function and reduce fruit disorders such as blossom end rot, white tissue, blotchy ripening and yellow shoulders.
In the past, a rule of thumb has been to switch to white or reflective mulch in the middle of June when days are longer and air temperatures are higher for a longer period of time.
Is there an advantage to switching earlier? Up to the middle of May, black plastic (or other soil heating colors) should be the preferred mulch to get plants off to a good start when soil temperatures can be variable and bed heating improves crop performance. The second half of May can see some very hot weather as can the beginning of June but this varies from season to season. If we continue to see warming trends and long range forecasts are for warmer than normal temperatures, laying white or reflective plastic for late May and early June may be advised for sensitive crops such as tomatoes and peppers.