How to Water Effectively

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Ill.: clipart-library.com

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 wateringalways 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:

Sun and wind have a drying effect on plants. Ill.: busy.org
  • 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.

Rule Breakers

If the Golden Rule of Watering applies do 95% of all plants, there are a few plants that break it.

Cardinal flower (Lobelia cardinalis) is a stunning perennial… but you have to keep it soaking most of the time. Photo: http://www.lakeregionnursery.com

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

Waiting for plants to wilt before you water them is not a good practice. Photo: G. Holmes, Cal Poly, Bugwood.org

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 easy and accurate. Ill.: Claire Tourigny, Les 1500 trucs du jardinier paresseux

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.

Moisture meters are excellent tools. When they start giving false results, after about a year, just buy a new one. Photo: amazon.ca

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.

Watering Tips

Dig a hole do see how deep the water you applied has reached. Ill.: Claire Tourigny, Les 1500 trucs du jardinier paresseux
  • 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.
Irrigation systems can do a great job, but need careful monitoring so they don’t overwater. Photo: wichita-sprinklers.com
  • 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.
Soaker hose is efficient and inexpensive. Photo: youngurbanfarmers.com
  • 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.
Water when you municipality allows it or face the consequences! Ill.: Claire Tourigny, Les 1500 trucs du jardinier paresseux
  • 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.

How to Tell If You’ve Watered Enough?

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A common mistake of novice gardeners is to water often, but superficially. Many in fact water every day, rapidly spraying the soil with water, then moving on. The result of this shallow watering is that only the surface soil is moistened. Unless there is good rainfall to compensate, plants grown this way react by producing mostly superficial roots, in the upper 2 inches (5 cm) of soil, a situation that leaves plants in risk of serious drought stress, especially if the weather becomes hot and dry.

Ideally, you’d water less often, but for a longer period, enough to soak the soil thoroughly. When rainfall is absent, watering once a week may be enough where temperatures are moderate and the soil holds water well, while a twice-weekly watering is more likely to be required in a hot, dry climate or where the soil retains little water. These infrequent but abundant waterings ensure that the water penetrates far into the soil, which stimulates the plants to also produce roots that extend to all levels, even fairly deep into the ground. That way, if the upper part of the soil starts to dry out, the plant can still find water and won’t suffer.

Please not that this tip is designed for people gardening in the ground. Plants grown in pots are in a very different situation. True, they still need deep watering every time, but they also dry out far more quickly than in-ground plants. In many cases, it may be necessary to water container plants daily, especially if the pot is small, because their root system is limited to the soil inside the pot and has nowhere to go for water in case of drought.

But how do you know if you’ve watered enough? There are so many factors that come into play—type of plant, planting density, presence or absence of weeds, presence or absence of mulch, rain in recent days, type of soil (dense or light, clay or sand), etc.—that it really isn’t possible to tell just like that.

To get a better idea, though, there is a simple test you can do.

Dig a hole in the ground to see how far the water has managed to penetrate. Ill.: Claire Tourigny, from the book Les 1500 trucs du jardinier paresseux.

About an hour after carrying out what you thought was a “thorough watering”, dig a small hole in the soil. If the soil is moist to a depth of at least 6 inches (15 cm), all is well. You can tell the soil is moist, because it will be darker than dry soil. However, if the soil is only moist to a depth of 2 to 4 inches (5 or 10 cm), the plants didn’t receive enough water. Water again. And water for a longer period next time.

Over time, most gardeners pick up the habit of watering thoroughly without wasting water, but in the beginning, it’s better to check first-hand to see if you’re doing it right!

The World’s Best Moisture Meter

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You’re not sure whether it’s time to water your vegetables, your flowerbeds, your houseplants, etc.? I know the perfect moisture meter, one which gives totally accurate results every time… and you already have it on hand.

20150713AThis extraordinary tool is… your index finger (or if you do not have an index finger, any other functional finger).

Here’s the technique:

Insert your finger into the soil up to the second joint. If the soil is dry to the touch, water. If the soil is moist to the touch, don’t water.

Repeat as needed every 2 or 3 days (for garden plants and houseplants) or daily (flower boxes exposed to full sun).

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Moisture meters are widely available, but not as accurate as your finger.

Obviously, there are plenty of commercial moisture meters that are supposed to accurately read soil moisture levels, but they often give false results, especially in certain types of soil. Moreover, they tend become contaminated with mineral salts after only a few months of use and then stop working properly. Your finger, on the other hand, will continue to give accurate results for 40, 60, or even 80 years.

Sometimes gardening can be so simple!