This summer I have received many phone calls and emails asking what should be done to help native plants that have been stressed due to fire and/or very dry conditions. In many cases the best prescription is to let nature take care of everything, but when the plants are located in easy view of your home or walking path, many people do not want to wait for Mother Nature to do her work.
Native plants commonly respond to drought by dropping their leaves. This is the plant’s way of dealing with a shortage of water and is cosmetic in that the long-term health of the plant is not usually affected. On deciduous plants, total leaf drop may occur much earlier than usual this year. On conifers, a tree may drop all of its needles except the needles that grew this year and last year. This sacrifice of older foliage enables the plant to use less water and protects the younger high food-producing foliage to ensure its long-term survival. The cost to the tree is stunted growth—we will see a much smaller “tree ring” for this season.
Other conifers will have some limbs completely die back, or in more severe cases, major portions of the top of the canopy will die off. I have seen thousands of Douglas-fir growing on very gravelly sites with 25 percent to 50 percent of their tops completely bare of needles. Watering these trees to prevent this kind of damage would be a major undertaking. You would need to water the total area from the trunk to six feet past the drip line with enough water to equal two inches of rain. On a 20-foot Douglas fir that would be over 200 gallons of water every week per tree.
Just say ‘no’
When we see our broadleaf evergreen plants like rhododendrons, salal, ferns, or evergreen huckleberry wilting, we want to water. Do not do it. These plants have great root reserves which will produce new replacement branches and foliage next year. If the plants are very wilted but not losing their leaves, they have gone dormant. If you water them you will break that dormancy and then you will need to water them every week to keep them from stressing and dying.
I have tested this with my native plant plots. The ones I left alone perked up after the first fall rains. They lost some of their branches and limbs, but the next spring they put up new ones. The ones I watered during the dry season looked good for only a few days before needing water again. When I continued to water these, they often put out new growth in the fall that was killed by frost. If I did not continue to water them after dormancy was broken, they would often die to the ground, and the next spring as few as 30 percent put up new growth.
Drought stress will be greatest on new seedlings planted this spring. They do not have the root size to pull enough water to the tree to keep all the growth alive. Consider fall planting, if conditions allow, to replace dead seedlings. This gives the roots more time to expand before the next dry season. If you are planting just a few trees or shrubs you can apply leaf mulch around the seedling to help keep the soil moist, but this can also be a good place for rodents to hide. Also, never fertilize new seedlings. The use of a high-nitrogen fertilizer will stimulate new top growth without corresponding root growth, which makes the new seedlings even more susceptible to very dry conditions. There has been some work showing that planting seedlings in among native brush may help protect them from extreme heat.
Smart pruning, better selection
Winter pruning of trees to cut the amount of foliage needing water will help the tree survive future droughts. Make sure that you keep 50 percent of the tree height in live crown to provide food for the tree, and wait until the tree is completely dormant. Pruning too early may cause the tree to produce new shoots which put even more stress on the tree, and the new foliage will be susceptible to early freezes. Pruned branches can be used for Christmas greenery and make great gifts as part of wreath kit for your family and friends.
The most important thing you can do to help mitigate the effects of long dry summers is to select native plants adapted to your soil and site qualities.
For example, ponderosa, white and lodgepole pines are more adaptable to very dry sites than many other trees, having deeper root systems and waxier needles to prevent moisture loss.
By working with nature to select plants from ground covers to the trees that are best suited for your site, you will ensure their long-term survival. Plan a walk through your forest this fall and winter to assess which plants are doing well after this severe drought, for future reference. Also be on the lookout for damaged limbs, or plants that need to be cut back to the ground to start again, and mark them for removal during the winter.
One last thought. If you have lost trees due to the dry conditions and the dead standing snags are not a danger to your home or access trails, save them for the wildlife. These trees will last a long time and provide great habitat for many different animals.
By Jim Freed, Extension Forest Products Specialist, Washington State University, firstname.lastname@example.org