Wednesday, August 4, 2021
Aug. 4, 2021

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Gardening with Allen: Cut back heat-damaged plants

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The recent intense heat wave has left some of my flowers and shrubs with burned leaves and blooms. Should I cut them back or just remove the brown leaves and blooms? Is there some way to prevent damage if we have another heat wave?

The recent heat wave has indeed damaged a lot of plants. Container plants were the hardest hit followed by plants in the hottest locations. Rhododendrons and hydrangeas were two of the most damaged shrubs. I even noticed trees that were damaged.

I noticed a wide range of damage on a particular plant, David Viburnum which was planted on all sides of an apartment complex. Plants on the west and south sides had the most damage. Those on the east side had less damage while those on the north side had no damage. Many of the flower beds had their entire bloom burned along with some leaves.

Plants have a transpiration system similar to the perspiration system in animals. Water moves from the roots through the stems to the leaves. Water evaporates from pores in the leaves and flowers to cool them similar to the way our sweat cools us. This transpiration acts as a pump, bringing water up from the roots. The flowers and the new leaves are at the end of the system and are the first damaged if plants cannot provide enough water for cooling.

Container plants have a more limited root system and cannot provide as much water. They are sometimes damaged even when their soil is not completely dry.

Some damaged plants have already dropped their dead flowers and some of their brown leaves. However, removing the remaining dead leaves will not only improve appearance but will stimulate new growth. Where there are several brown leaves connected by a stem, the whole stem should be clipped off just above the first undamaged leaf. This will stimulate the most new growth.

Trees may need professional pruning by an arborist.

Of course the most important thing to do if we have similar 100 degree plus heat waves is to keep plants well irrigated. Container plants may need more than once a day watering. I am concerned about trees that showed no damage having major damage later with dry weather in the 90s. Trees which are beyond any irrigation system are particularly vulnerable. Some deep watering of trees is very advisable.

Container plants can be temporarily moved to shadier locations.

Covering plants with white cloth-like sheets will not only provide shade but reflect the light and heat. Even newspaper or other white paper can be used.

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