Do Water Deeply
The most important thing to remember when watering containers is to water deeply—this means that you should see water running out of the drainage holes at the bottom of the container. If you don’t see watering flowing from the bottom of the container, you have not watered enough. Healthy root systems quickly grow and branch out through the soil towards the bottom of the container. Drenching the container ensures that water reaches the entire root system. Watering deeply encourages plants to develop strong root systems, and that provides better nutrition for the plants. Frequent shallow waterings encourages roots to remain near the soil surface where they are more susceptible to heat and drought and with less ability to absorb nutrients that are available deeper in the container.
Do Water in the Morning
Plants are more receptive to watering in the morning and less so in the midday sun. Morning is ideal because it provides sufficient moisture to the plants for the entire day, there is less evaporation caused by wind and heat, and it allows wet foliage to dry out before nightfall. Watering in the evening is not recommended because the foliage does not have enough time to dry before the sun goes down. Wet foliage can invite fungal diseases such as powdery mildew. Not everyone has the opportunity to water containers in the morning given time pressures of getting children to school or heading off to jobs. If you can’t water containers in the morning, water them when they’re dry no matter what time of day it is.
Do Water the Soil, Not the Foliage
Plants absorb water through their root systems, not through their leaves, stems, or flowers. Thus, to properly water your containers, apply water to the soil where it will reach and be absorbed by the plant roots. Wetting foliage can lead to an increased chance of fungal and other diseases and the water is wasted anyway. Another reason to keep foliage dry when you water is that some plants—especially those with hairy leaves—can be susceptible to sunburn in the hot sun. Water droplets attach themselves to tiny hairs, and when water collects on them, it’s possible that the water droplets act like mini-magnifying glasses. Sunburn won’t occur on smooth-surfaced leaves.
Don’t Rely on Rain
Even if you think a rain shower has watered your containers, don’t be so certain because it’s usually not true. Plant foliage can act like an umbrella and actually prevent water from reaching the soil. With containers filled with mature plants, soil might not even be visible so it’s impossible for rain to penetrate the thick growth. Rainfall amounts, even those from a heavy storm, might not be nearly enough to fully saturate container soil from top to bottom. Take matters into your own hands and monitor container moisture yourself, even after a heavy rainfall.
Don’t Let the Soil Dry Out Completely
Most potting mixes become tough, hard, and stop absorbing water efficiently if you let them completely dry out. Dried out potting mix can also pull away from the sides of containers. So while you might think you are applying enough water, the water might be flowing down the sides of the container and out the bottom, leaving your plants gasping for water.
If the container soil dries out, here are two methods to re-hydrate them:
- If the container is relatively small, fully submerge it inside a larger container or sink filled with water. Remove the small container when it has stopped bubbling.
- If the container is large and is difficult to move or lift, poke a few holes into the soil with a pencil or skewer. Then apply a gentle, slow stream of water to the soil making sure the soil is absorbing the water. Repeat this process until the soil is softened and fully moist.
Don’t Assume Once Is Enough
Depending on the climate, the size of your containers, and the kind of soil you use, don’t be surprised if you have to water your containers more than once a day. Heat, wind, and dry air can quickly parch your plants. Metal and terra cotta containers and hanging baskets made from coir can dry out incredibly fast on a hot, windy summer day.
Over the growing season, you will know which of your containers and hanging baskets dry out the fastest. When your containers are first planted, monitor them for moisture in the morning and then again in the afternoon to see which containers might require more watering than others. You might find that watering once in the morning simply is not enough. A small container (ten inches or less in diameter) might require three daily waterings during brutally hot and dry weather.
Check Moisture Levels
Before watering a container, be sure that the plants need water. Over-watering is just as harmful as under-watering. The soil at surface of the container might look and feel dry to the touch, but the soil might be moist just an inch or two below the surface. To test container moisture, try this: stick your finger into the soil as far as it goes or at least to your second knuckle. If the soil feels dry at your fingertips, the plants need water. Moisture levels can change quickly on a hot summer day, so a container that feels quite moist in the morning might be dry by mid-afternoon.