Fall In the Xeriscape
Watering in the fall can be particularly problematic. Conditions continue to be dry and trees, shrubs, and lawns need water to avoid stress. Too little water during the fall and winter months can cause root die-off, something that may not be noticeable until well into the next growing season. Water stress during fall and winter can also mean that weakened plants will be more susceptible to insects and disease come summer. Too much water during these seasons can be a bad thing. In areas where there are water restrictions, autumn may require you to do more with even less.
Here’s an excellent article on watering trees and shrubs in the fall from the Colorado State University Extension Service. Some takeaways: shrubs and perennials with shallow root systems are most in need of water during these seasons to avoid root die-off. Mulch is important, not just in keeping moisture in the soil but to prevent soil from cracking (cracks allow cold to invade to greater depths, risking tender roots). Don’t water when temperatures are below 40 degrees; there’s a good chance soil moisture will freeze and damage roots. Water at mid-day so moisture will have a chance to soak into the ground before night-time freezes.
Here are some other tips from Gayle Weinstein’s excellent book Xeriscape Handbook: A How-To Guide to Natural, Resource-Wise Gardening. Do not fertilize (compost, of course, is okay, even encouraged when used as a mulch) or prune during times when water is scarce. If you do prune — and fall is a traditional pruning time — don’t water. This may seem contradictory but the point is that pruning encourages growth which requires water. If the plant doesn’t have enough stored, it will suffer future damage. Wait until all chance of growth has passed, as late as November and December in some places, before pruning. And don’t use pesticides. Pesticides may disrupt normal plant process and put plants under stress, making them susceptible to injury.
Lawns, too, need water in the fall, especially if the season is dry in your area. If you’re getting plenty of fall rain, then don’t bother. But a light watering to soak root crowns is necessary to make sure you have a healthy lawn come spring. Newly planted or sodded lawns need regular thorough watering, of course. Again, water in mid -day to prevent overnight freezing. In cooler climates, once the ground begins to freeze (or there’s a snow cover) your lawn watering days are over. In milder climates, water anytime in the fall or winter that your lawns don’t get a good soaking from Mother Nature. An inch of moisture, either from you or from the skies, every couple weeks is a good idea. Trying to save water? Then why have a lawn at all? Go with drought-tolerant locally-adapted plants instead.