This may sound a bit obvious to experienced gardeners, but incorrect watering is a major cause of failure for beginning gardeners. They don’t water often enough, or water too often and, inevitably, don’t water deeply enough. So, let’s look at that here.
The Golden Rule
First, learn the golden rule of watering: always water slowly and deeply, providing enough water to moisten the entire root system, then wait until the soil is dry before watering again. This rule applies just as well to moisture-loving plants, like ferns, as desert dwellers, like cactus. If you learn that rule and always follow it, you’ll have the greenest thumb in town.
Factors to Consider
Of course, not all plants use their water at the same speed, so one plant may be so dry it begins to wilt only three days after you water while another can still be weeks away from needing watering again. Here are some of the factors that make a difference:
- Intense sun leads to greater watering needs; shade reduces watering needs.
- Hot weather leads to greater water loss to evaporation and thus more frequent watering.
- Windy spots dry out more quickly than protected ones.
- Sandy soils dry out more quickly than loamy ones. Clay soils dry out even more slowly.
- Plants with large, soft leaves need more watering than plants with smaller, thicker ones. Plants with really thick leaves (succulents) can go for weeks without watering.
- Plants with leaves coated in fuzz, hair, bloom or wax leaves lose water more slowly than those without such coverings.
- Plants with thin stems need more water than those with thick ones. Again, succulents, with often hugely thick stems, are the most drought resistant.
- Plants in containers need more water than plants in the ground.
- Plants that are dormant need little to no water until they reawaken.
- Plants in bloom or producing seed need more water than those just in leaf.
- Most plants grow most quickly in spring and need more water then.
If the Golden Rule of Watering applies do 95% of all plants, there are a few plants that break it.
One group that doesn’t follow the rule is marsh plants; semi-aquatic plants if you prefer. They’d like to always grow in moist, even wet soil and should never be allowed to dry out in the slightest. These plants, like cardinal flower (Lobelia cardinalis) and cattails (Typha spp.), usually grow in swamps or near bodies of water in the wild. They can rarely share their growing space with other garden plants, so give them their own special environment.
Of course, actual aquatic plants, like waterlilies (Nymphaea spp.) are even more dependant on moisture and like their roots to be always underwater.
The other rule breakers are plants that go dormant. They usually like to be watered like any other plant during their growing season, but when they lose their leaves (most do), they’re telling you: keep that hose away from me. Many cactus, succulents and bulbs have long, dry dormant periods.
How to Know When to Water
Don’t wait for plants to wilt before you water. If leaves wilt from lack of water, likely some of the plant’s roots will have died and that’s not good for the plant. Some plants, indeed, never fully recover if you let them wilt! And then there are a few plants with large, thin leaves, like ligularias (Ligularia spp.), morning glories (Ipomoea spp.), squashes (Cucurbita spp.) and butterburs (Petasites spp.), that wilt dramatically on a hot day, yet their soil may still be quite moist. If so, watering won’t help them. So, wilting is not a good measure of watering needs.
The finger test is a sure way to tell if a plant needs water. Stick your index finger into the soil to the second joint. If the soil feels moist, don’t water. If it feels dry, water.
Some people prefer a moisture meter to their finger. You stick the tip of the meter into the ground and the gauge indicates whether the plant needs water.
Or push a spade into the soil and take a gander. Moist soil is darker than dry soil and if the soil is clearly moist to a depth of 6 to 12 inches (15 to 30 cm), the plant doesn’t yet need water.
You can often gauge the needs of container plants by lifting them, although this takes some practice. If the pot seems light, it needs water; if it seems heavy, hold off for a while.
- Always water slowly and deeply. A quick shower only moistens the top of the soil, leaving plants water-stressed; you need water to sink in to a decent depth. At least 6 inches (15 cm) for lawn grasses and annuals; at least 12 inches (30 cm) for perennials, trees and shrubs. The first few times you water any garden, dig a quick hole about an hour after you finish to make sure the soil has been moistened to the proper depth.
- Water the soil, not the leaves. Most plants absorb little moisture from their leaves (aside from air plants [Tillandsia spp.]). It’s the roots you need to water. In fact, the ideal situation is to water carefully so as to moisten the roots while keeping the leaves dry, as wet leaves are more susceptible to disease.
- Water in the morning if you can. If you get moisture on the leaves, this gives them time to dry out. Water at midday only if you have no other choice, as, in the heat of the day, much of the water will simply evaporate without helping the plants. Watering in the evening, when temperatures have dropped and evaporation will have decreased, is the second best choice, but try to keep water off the leaves, otherwise they’ll spend the night moist and that can lead to disease.
- Water only as needed. Remember that Mother Nature contributes to watering with her rainfall and sometimes, even often in many climates, she does fine on her own.
- New plants need more frequent watering, as their root system is not yet fully developed. The secret here is to water just as the soil starts to dry out, not to leave them soaking in water at all times. Water transplants of annuals and vegetables more for the first two weeks and perennials, shrubs and trees more for the first season.
- Automatic watering systems can be wonderful … if they’re well adjusted. They should include a rain sensor that delays watering when Ma Nature steps in. You’ll also have to adjust the system throughout the season, watering more in the heat of summer than the cool of spring and fall. Remember, overwatering does as much damage as underwatering!
- Mulch all your plantings. Mulch reduces surface runoff, keeps roots cooler and slows evaporation from the soil, seriously reducing watering needs.
- Use good watering tools. A soaker hose offers efficient watering (properly installed, it can use up to 75% less water than a sprinkler system) and keeps leaves dry, preventing disease. Drip irrigation is a more expensive way of accomplishing the same thing. Sprinklers are better than nothing, but waste a lot of water. Hand watering (with a watering can or hose-end sprayer) gives you better control, but is time consuming. Take it slowly if you hand water, remembering you need to water enough to soak the entire root zone.
- Follow local watering restrictions, no matter how illogical they may be. (They’re designed to reduce stress on municipal water systems, not to grow better plants!) After all, who wants to pay a fine for watering at the wrong time or with the wrong device?
If watering sounds complicated, it really isn’t. Once you get a handle on it, you’ll find you’ll become quite the expert.