Dry summers are not that unusual in the Midwest, but this year’s weather pattern was a bit unusual in that much of the state experienced above normal precipitation in spring and early summer. But most areas found the flow of water shut off in mid to late summer. Many plants will be displaying their fall colors and dropping leaves in the next few weeks, but this is a critical time for plants to rehydrate themselves before the onset of winter.
Though trees, shrubs, and hardy perennials will be dormant in the winter, all roots, woody stems, and evergreen leaves will continue to lose moisture through the biological process known as transpiration. Once the ground freezes in winter, plant roots will no longer be able to take up moisture from the surrounding soil. Yet the plant tissues continue to lose water throughout the winter and this drying is further aggravated by high winds.
So your job as head gardener of your landscape is to make sure the plants are as fully hydrated as possible before the onslaught of winter. The best way to apply the water is by gently, but thoroughly, soaking the soil with about 1 to 1 1/2 inches of water every 7&endash;10 days. This deep watering will encourage deeper root growth that in turn will be better able to withstand periods of low moisture. Frequent shallow watering encourages shallow roots that are more likely to succumb to heat and drying of the top soil. Sandy soil and containerized plants will need more frequent irrigation.
Another important consideration is that next year’s growth will be determined by buds that form this fall. Flower buds for spring flowering and fruiting plants will also be developing this autumn. So even if your plants aren’t showing any symptoms now, the damage may become apparent later.
Watering of landscape and fruit plants should be aimed at where the roots naturally occur. While these woody plants do have some roots that grow very deep, most of the feeder roots that are responsible for water uptake occur in the top 18 inches of soil. Most of these feeder roots are concentrated below the dripline of the plant and beyond, not up close to the trunk. Allow water to thoroughly soak the target area by applying water at a slow enough rate to allow penetration rather than wasting water by runoff. Don’t apply the water any faster than 1 inch per hour. As with annual plants, a mulch will help prevent moisture loss due to evaporation.
The amount of time it takes to apply the proper amount of water depends on how much water pressure you have, the amount of space you need to cover, air temperature, and wind speed. You’ll need about 50 gallons of water to apply 1 inch of water to a 100 square foot area.
The ideal time to water is during the early morning hours, ending by 8:00 a.m. This makes maximum use of water while allowing foliage to dry. Watering during midday when temperatures are high, sunshine is strong, and winds are brisk wastes substantial water. Watering in the evening or at night is convenient for many, but can make plants more susceptible to disease infection by providing the moisture that fungi and bacteria need to grow.
Last updated: 6 April 2006