Fall Drought Stress

Robert Bishop 
Frederick County Master Gardener Program

In the last six weeks the metro D.C. area has only received 0.02 inches of rain. Most people are not aware of how dry things are because the air temperatures are cool. The leaves are falling and we are starting to concentrate on the approaching holidays not worrying too much about our plants. Visual inspection of our landscape plant material reveals few problems. The fact is the soil is very dry and the time to water is now. All plants will benefit from at least one more heavy watering before you turn your hose bibs off for the winter. Plan on watering the entire landscape.

It is important to understand that although the heavy fall frosts have slowed or stopped most of the above ground growth for this season, but below the soil surface there is much going on. Soil temperatures are still warm enough for root systems to grow and food reserves are being stored in roots as well at this time. Water is essential for any growth process. Large healthy root systems have the advantage of being able to draw water from a larger soil mass, this in turn reduces the year round drought risk to the plant. The larger the root system the better, a dry fall limits the amount of root growth.

Another consideration is the special winter needs of evergreen plants. Because they retain their leaves all year, they need to replace water all year that is lost through transpiration, although they require less through the winter months. Evergreens are divided into two groups, the needled evergreens like pine and spruce; and the broadleaf evergreens like rhododendrons and cherry laurel. Both require water all year long.

Broadleaf evergreens are very susceptible to winter burn due to their large leaf surface area. Winter burn occurs when dry winter winds pull water from the leaves faster than the plant can replace it. Fall and winter drought stress can increase this type of damage. The symptoms are obvious, the leaf edges die and turn brown. Broadleaf evergreens are especially vulnerable for the first few years after planting due to their small root system which can only take in water from a small area. It is best to try to protect them from winds and water them on those warm, sunny winter days.

Read other articles by Robert Bishop