Sunburned plants

This article provides advice about how to recognize sunburned plants (sunscald), how to prevent it and what to do if your plants suffer from it.

Marjory Blare, Master Gardener

Many plants in your vegetable garden can get sunburned! For instance, vegetables and fruit can burn if the canopy of leaves over them is removed or if they are placed outside without being hardened off. House plants will suffer if moved from a shady room to a sunnier room. Sunscald is a synonym of sunburned.

How to recognize sunburn/scald

Look for: sunken bleached spots on fruits and vegetables; brown areas on pome fruits such as apples; or whitish, yellowish or browned foliage.

Some things to do to prevent sunburn or sunscald

1) Harden-off plants before moving them to a sunnier location. Over the course of about 5-10 days, let them have longer and longer exposure to the sun (and wind). This goes for houseplants moving to a sunnier room or outside, as well as seedlings and plants grown in a greenhouse.

2) Plant out on an overcast day, if possible.

3) Water thoroughly before and after planting out.

4) In the case of house plants, research ideal light conditions and then observe the new location for several days in advance of moving them.

5) Water in the morning, and water at the root instead of the foliage. Water on leaves can magnify the sun to cause damage.

6) Be careful to not remove foliage shading immature fruit/vegetables when harvesting; this will let the sun reach areas that aren’t used to it.

7) Research whether your fruit/vegetable will continue ripening after picking and possibly pick them a little early, then promptly get them into the shade or a cooler place.

8) Try a different variety if you notice lots of sunscald this year.

9) Mulch freshly planted starts to conserve moisture, and facilitate root growth.

10) Do not fertilize right away; a high nitrogen fertilizer will direct energy into the leaves before the roots can settle in.

11) Kaolin- based products such as Surround® can reduce the chances of sunburn. Read the label for proper application rates and personal protective equipment. The label for Surround WP® includes language about reducing sunburn damage, but Surround CF® doesn’t. This product covers the surface of the fruit with clay. The clay will reflect the sunlight and reduce the sunlight that reaches the fruit. Kaolin should be applied to the point of near-drip coverage. Be careful to leave enough foliage free of the kaolin for photosynthesis. Check label for organic certification. Read more about the use of Kaolin from Purdue University here: https://vegcropshotline.org/article/sunburn-on-vegetables/

12) Prune carefully to leave enough foliage to shade the fruit/vegetable. Prune diseased foliage promptly.

13) Water deeply.

14) Sheer curtains in the window can help house plants deal with too much light.

15) Use a shade cloth or bamboo screen to throw some shade during the hottest part of the day, and growing season. Shade cloth differs in the amount of shade that is thrown. A 70% cloth will let 30% of the light through. There is no one, right, answer to which percentage your garden needs. I used an orange snow fence last summer.

Some things you can do after a plant shows sunburn/sunscald

1) Move plants (if possible) to a less exposed site.

2) Cut fertilizer rates to half strength until new leaf growth shows.

3) For tomatoes, try to keep temperatures below 95 degrees Fahrenheit. Tomatoes are native to alpine regions in Central and South America. The hottest days of Minnesota’s growing season can be hard on tomatoes. Try a shade cloth or bamboo screen to keep the tomatoes cooler during the hottest parts of the day.

4) Remove damaged fruit or leaves so that the plant can use its energy to grow more fruits, vegetables or leaves.

5) Be patient.

Planning to prevent sunburn/scald before it can happen will lead to a happy productive garden!

Photo credits: Marjory Blare (1, 3), Dreamtime.com (2), istockphoto.com (4)