What to do and when to Prune for Heat Damage on Garden Shrubs
Leaf scorch and leaf drop symptoms as a result of the late June scorching temperatures are continuing to appear on many garden shrubs and small trees. Discrete areas of leaf scorch and twig dieback may continue to show up where the sun beat down like a laser beam, burning the life out of those tissues. Seeing these symptoms can make it tempting to clean them up right away. But there is more to consider before you head out to the garden with pruners in hand:
Relieve moisture stress first
Overall drought stress symptoms may show up in the yellowing and shedding of interior foliage. Check soil moisture and give affected plants in dry ground a slow deep soak (at least several inches). Use a trowel to inspect moisture penetration. Use a wetting agent if the soil has become water repellant. Products like Soil Moist Water Aide, Yucca Wet, or a little bit of mild castile soap mixed in a watering can work like magic to pre-moisten really dry ground ahead of regular watering. Evening and early morning hours are good times to water for optimal rehydration of water-deficient plants. Watering deeply and infrequently will give plants greater drought resilience than shallow sprinkling every day or two.
Wait and see what happens to stems with brown leaves
Leaves with too much damage to function will be shed and well-hydrated plants are likely to put on replacement growth. Leaves with smaller areas of damage will continue to provide energy needed for new growth. Accept some imperfection in appearance and don't be too hasty to dive into pruning where there are discolored leaves. Wait a few weeks to see what has died and where renewed growth has begun. Keep up periodic watering, but don't fertilize at this time.
Remove clearly dead branches
If the stems have shriveled and there's no sign of bright green cambium showing when you scratch through the bark, those dead and near dead branches can be removed. Place cuts back to a natural point of attachment at healthy wood as for routine pruning to natural form.
Avoid pruning shrubs that are wilted or show other drought stress symptoms
As with all summer pruning, make sure plants are well hydrated beforehand, prune lightly, and be aware that exposing previously shaded foliage can make them susceptible to scorch. Avoid pruning in hot direct sun and/or on high temperature days to prevent heat stress to plants and gardeners alike.
Christina Pfeiffer
PlantAmnesty Member & Instructor
ISA Certified Arborist®