Regional Gardening Reports :: National Gardening Association

In the Garden:
Middle South
July, 2009
Regional Report

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Some drought-tolerant plants, such as these container-grown succulents, store water in their thick, fleshy leaves.

Garden Smarter, Not Harder

Last summer, in the face of severe drought, I collected excess sink and shower water in buckets to irrigate my parched landscape. Thankfully, rains have been plentiful in the first six months of 2009. For the first time in nearly 3 years, no part of South Carolina is under a drought declaration.

Now that July has arrived, however, hot and dry weather is sure to follow. While I hope to give the buckets a rest this summer, I'll continue to garden smarter by adding more drought-tolerant plants and utilizing water-wise practices.

To understand the effects of summer weather, it's helpful to know some of the basics about how water moves through plants.

Most gardeners understand that water enters a plant through its roots. Less well known is the fact that the plant loses about 99% of that moisture as water vapor from its leaves in a process called transpiration.

Transpiration keeps plants cool, in the same way that sweat evaporating from our skin keeps us from overheating. It also acts as a vacuum, pulling water cell to cell -- from root to leaf -- even in the tallest trees. In fact, it is the process of losing water that provides moisture to all parts of the plant.

When air around a plant is hot, dry, or windy, transpiration rates are higher and the plant requires more moisture to remain hydrated.

Drought-tolerant plants survive moderate periods of limited moisture by conserving or storing water. Most hollies, for instance, with their small, thick leaves covered in a waxy coating will lose less water on a hot day than plants with large, thin, unprotected leaves.

Other plants conserve moisture with small leaf hairs that reflect light, shade the leaf, and reduce air flow over the leaf's surface. Most plants also carefully regulate their stomates -- the pores on the undersides of the leaves which open and close to permit transpiration.

Succulents store water in thick, fleshy leaves and open their stomates only at night, expelling oxygen and taking in carbon dioxide for the next day's photosynthesis.

Particular root systems also make some plants drought tolerant. For example, plants that have both surface roots and tap roots can capture moisture from light rains as well as deeper water. Plants with fibrous root systems, on the other hand, collect most of the rain before it can penetrate into the soil.

Whether or not your garden is filled with plants that can conserve or store moisture, prudent garden practices can reduce the season's harsh impact on your garden.

First, when water is in short supply, give the highest priority to newly planted trees, shrubs, and perennials; newly seeded lawns; vegetables in flower; and plants on fast-draining soils and in windy or exposed sites. Irrigate early in the morning to reduce evaporation and always water deeply to encourage healthy roots.

Be cautious with pesticides, never applying them in extreme heat, as they place additional stress on plants.

You should fertilize less, too, in both frequency and amount, to restrict excessive growth. It is particularly important to avoid high-nitrogen fertilizers during the hottest months. In general, organic fertilizers are more gentle. They also add humus to the soil, aiding water retention.

Cultivate the garden sparingly, as disturbing the soil surface will make it dry faster. To keep weeds in check, mow or cut them off at the soil's surface.

Don't prune in July or August either, as cuts will be slower to heal. Remember, pruning encourages new growth, which also increases the need for water.

When mowing, forget the bagger and leave grass clippings on the lawn to recycle nutrients and moisture.

Finally, use several inches of organic mulch to prevent soil from drying. Keep it several inches away from the trunk of woody plants, however, to prevent bark rot and reduce insect problems. As a bonus, the mulch will also help moderate soil temperature, discourage weeds, and build soil.

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