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Fall Watering Guide

Fall Watering Guide - 2019

People rightfully consider fall to be the end of the growing season, but that’s certainly not how plants see it: for shrubs and perennials, fall is prime time for root growth. Once they’ve gotten a break from supporting leaves and flowers all summer, they devote their energies underground to the roots. Typically, fall weather is ideal for root growth: sunny, warm days, cool but not-quite-cold nights, and good soaking rains once a week or so. However, the season is notoriously unpredictable, and when we experience an unusually dry fall, there’s simply no getting around it: we must water our plants to help them make the most of the root growing season.

Fall watering isn’t as intensive summer watering – if your irrigation system has been winterized, there’s no need to get it running again. You won’t need to water every day, and you’ll only need to water if you haven’t had a soaking rain for 10-14 days. When you do water, make sure to completely saturate the soil; a hose-end sprinkler is a great choice to make sure the job gets done properly. A thorough watering twice a month during mid-late fall should be sufficient for most soils, though if you have slow-draining clay or rocky soils, you may find that just once a month is enough.

When autumn watering is necessary, evergreens deserve extra attention, as do plants that were added to your landscape that same year. New shrubs and perennials haven’t yet developed a substantial root system, and helping them take the best advantage of autumn will pay big dividends next season and beyond. Evergreens, with leaves present year-round, never get a reprieve from the drying forces of sun and wind. However, when the ground is frozen, their roots cannot take up water to replace what is lost through the leaves. As such, it is vitally important that evergreens of all types, but especially broadleaf evergreens like boxwood, holly, and rhododendron, enter the coldest season well-watered and free of stress. In fact, these plants are candidates for fall watering even when rainfall is normal, as it can minimize or even eliminate the unsightly browning that often occurs in winter with these species.

One final tip for happy roots any time of the year: mulch. A 2-3” (5-7.6 cm) layer of shredded bark mulch should be in place around all of your plants by the time winter rolls around. Mulch fosters rapid root growth, and maximizes the benefits of fall watering, whether you provide it or the rain does. Once the ground begins to freeze (or rainfall returns to normal), you can finally devote your energies to more seasonally appropriate activities, like watching football and making apple pies.

The Best Way to Water

Watering is of no value if the water runs down the outside of the root ball, leaving the roots at the core of the plant dry. This can happen if you water too quickly or apply too much water at once. Slower watering is usually more effective. The key is to ensure that water gets to the root zone — whether you are tending seedlings, watering houseplants, watering a row of tomatoes or soaking thirsty shrubs and trees.

You can't use the "lift test" in your garden or landscape, but you can use a soil moisture sensor to see if it's time to water. For a thorough investigation, push a spade into the soil near your plant and pull it back to see how the soil looks. If it feels moist to a depth of 6 to 12 inches, you're in good shape. If it's bone dry, water!

Six Tips For Watering Your Garden

Focus on the root zone. Remember that it's the roots that need access to water, not the leaves. Wetting the foliage is a waste of water and can promote the spread of disease.

Water only when needed. Automatic watering timers are especially useful; just make sure to watch the weather, and reduce frequency when rainfall is abundant. Too much moisture can be just as damaging to plants as too little.

Water deeply and thoroughly. Lawns and annuals concentrate their roots in the top 6" of soil; for perennials, shrubs and trees, it's the top 12". In heavy soil, it may take hours for water to percolate down 6-12". Use your finger or a shovel to check the progress.

Water in the morning. If you do get moisture on the leaves, this gives them time to dry out. It's much more difficult for plant diseases to get a foothold when the foliage is dry.

Mulch everything. Mulch reduces surface runoff and slows evaporation from the soil.

Use the right tool. For efficient watering at the root zone, use a soaker hose or an even more precise drip irrigation system instead of a sprinkler.