Watering: How Much and When?
(most folks get the basics wrong . . .)

Improper watering is the top cause of plant stress and the number one killer of houseplants.

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Water needs vary dramatically depending on the type of plant, soil and location. Weather factors such as temperature, humidity and wind also play a big part. It is easy to see why getting the watering thing right can be a challenge, so here are some tips.

 

Water Deep

The goal of watering is to get moisture to the roots so it can be absorbed and used by the entire plant. Many gardeners stop watering when the soil surface becomes wet or when water starts to puddle or run over the top of the pot.  Often this approach wets only the top inch or so of soil because water is absorbed slowly by heavy, dense and compacted soils. While the top is wet, the soil down by the roots could still be dry.

Check. Poke your finger, a trowel or a stick into the soil. Where is the water depth? Meaning, does the water reach the bottom of the roots? 

 

Avoid Guessing

 Each time you water, you want to apply enough water to moisten the soil to the bottom of the root zone. This is because the outer-most tips of the roots, where their circumference is the skinniest, is the most effective at absorbing water, whereas the top of the root system is thicker and serves a more structural and supportive role. 

To determine how much water you are already applying, it is essential to measure.  This will help determine if you are providing your plants enough water. 

Water is measured in inches. Place an empty tuna or cat food can or plastic Tupperware container on the lawn or in the garden when the sprinklers are on and when it rains. When the sprinklers stop, measure the water in the can. Now you know that your landscape is getting ½” or 1” per watering. No more guessing.

For most parts of the country, 1” of water per week is a good starting place. Modify this amount if your soil is sandy and drains quickly, or if you live in a dry, hot part of the country where moisture evaporates quickly. 

(If you want to get very precise, this webpage will help you calculate exactly how much and how often to water based on the plants you have, the area you are trying to cover, and the rate of emission of your hose of sprinkler.)

 

Timing is Crucial.

When you water matters. 

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Watering early in the day, between dawn and 9 am, is ideal as this allows plants to rehydrate before the sun bakes them. Evening watering makes foliage wet and thus prone to fungus attack. For this reason, it is not recommended.

 

Watering Pots, Window Boxes and Other Containers

First, choose containers that have drainage holes on the bottom side. This avoids having root-rotting water pool in the base of the pots.  Since the soil ball in most containers is limited, it is important that everything gets wet when you water. Keep your watering can tipped until you see water draining from the bottom of the container. If the container has a saucer, wait for all the water to drain through (10 – 15 minutes), and then empty the water from the saucer. This avoids standing water that can damage roots and provide breeding sites for mosquitoes. Should the drainage hole become blocked over time, poke a stick in the hole to loosen compacted soil.

If the container soil gets very dry it may shrink and pull away from the container walls. Then, when you water, the moisture can slip between the sides of the pot and the soil and right out the bottom. Watch for this and make sure all the soil is getting moisture. In extreme situations, you may need to submerge the entire pot in a large tub to rehydrate the shrunken soil ball.

 

Reevaluate as the Season Progresses

When temperatures are relatively cool, as in the spring, plants typically need less water. The same is true for little plants that do not yet have much biomass to support. Tweak your watering plans as the weather gets hotter (or cooler) and as plants grow larger.