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Container Gardening Basics: Watering Potted Plants

First posted on Mar 10, 2016

Container Gardening Basics: Watering Potted Plants

Container plantings are welcome islands of color and fragrance on balconies and in small urban yards. They enhance the decks, entryways and flowerbeds of homes with larger yards. And their emergence signals the pleasures of summer -- shorts and tees, long hours of sunlight and icy glasses of lemonade.

Container garden plans for Salvias and companion plants need to factor in greater frequency of watering than the plants would receive in-ground.

But as you slake your thirst, remember that potted plants have a mighty thirst, as well. Your potted Salvias and companion plants especially may need extra cool drinks of water on hot days. Container garden plans for Salvias and companion plants need to factor in greater frequency of watering than the plants would receive in-ground. At the same time, you need to keep in mind that plants are more easily over-watered in containers than in garden soil -- a peril for many species, including Salvias. Their roots can't get enough air when waterlogged.

Limited by container walls -- whether ceramic, metal, plastic, terra-cotta, wood or soft, fabric -- potting mix doesn't retain moisture or drain as easily as garden soil.

Following the Ups & Downs of Water

In a process called capillary action, water sticks together in droplets (cohesion) and to the sides of container walls and soil particles (adhesion). It travels down, back up and sideways like in a sponge.

Whether in the garden or in containers, plants contribute to the upward flow by acting like pumps that suck up water through roots and then release it to the atmosphere through leaves.

Regarding uptake, the USGS Water Science School notes, " As water molecule #1 starts climbing, it pulls along water molecule #2, which, of course, is dragging water molecule #3, and so on."

A plant consumes as much moisture as it needs. Waterlogging occurs when there is so much moisture in the plant's soil that its roots are surrounded and can't get the oxygen they need. This is particularly a problem for Salvias, most of which fail without good drainage.

Waterlogging is particularly a problem in containers, because capillary action is less vigorous in pots due to their limited amount of soil.  In the garden, it is easier for excess water to disperse downward.

One way to aid gravity in when growing Salvias in containers is to add extra mineral matter to potting mix. Grit, such as pumice particles, helps create pathways for water to escape. This improves aeration. Pumice, which is a lightweight volcanic rock, has lots of air holes. At the same time that it aids aeration, it also stores water for later access.

For more information about selecting potting mix, please read Container Gardening Basics: Selecting a Good Potting Mix.

Overwatering & Testing Moisture

Sogginess is bad for many plants, especially Salvias, which prefer soil that is only slightly moist. For shallow rooted sages, such as annual plantings, you can test the dryness of potting mix by poking your finger about 2 inches into the medium. Feel for moisture with your fingertip. For perennials in deeper pots, insert a long screwdriver or a thin dowel. Squeeze a bit of the soil bits together to see if they are mushy (bad), dusty (bad) or cling together (good).

One sign of overwatering is when a planter's drainage plate is full. A drainage plate not only helps you clear excess fluid but also airs the bottom of a planter by raising it above hard surfaces.

However, less frequently, a full drainage plate may also indicate that a plant has become hydrophobic due to underwatering. If a plant's rootball becomes bone dry, it is difficult to wet. An overly dry rootball may shrink and not accept water, which then drains out the pot hole. In that case, place the container (something porous, such as terra cotta) in a shallow dish of water to allow gradual re-moistening of the soil. Remove the pot from the water bowl before the soil becomes soggy.

How Much H2O is Just Right

But the watering question lingers. How much is enough for a container planting and what is too much?

Even if your pots contain drought-tolerant sages, you will need to water frequently. However, it may be once a day or every other day.

Selecting the right amount of water is related to container garden design. The combination of sages and companion plants you choose should consider similar needs for moisture.

Aside from doing poke tests, what factors do you need to consider in calculating a watering schedule for containerized sages? The answer to "How often?" depends on growing conditions, including:

  • Local precipitation and climate. How frequently does it rain or get foggy in your area. It may be that little supplemental watering is necessary or you need to water twice daily. Is your climate dry or humid?
  • Sun exposure. How much sun your do your container plantings need. Full sun plants also gain a larger dose of heat, which may increase evaporation depending on climate.
  • Watering times. Ask yourself whether you are selecting the most efficient times of day when watering. Evaporation tends to be lower early in the morning and in the evening.
  • Daily temperatures. Studying high and low temperatures can help in deciding when to increase or decrease watering.
  • Seasonal changes. While some regions have wet winters and dry summers, other areas are just the opposite. Watering needs to be adjusted to reflect changes in precipitation and temperature from one season to the next.
  • Container choices. The type of planter you choose may increase or decrease watering.   For more information, please read Container Gardening Basics: Selecting and Arranging Pots.

Finally,  selecting the right amount of water is related to container garden design. The combination of sages and companion plants you choose should consider similar needs for moisture. 

Reaching Out for Advice

If given the right conditions, including proper watering, many easy-to-grow perennial and annual Salvias grow beautifully in containers. Their roots likely won't stretch as deep or wide in search of water as they would in open soil, so size will be somewhat miniaturized. This is helpful when you love a plant's flowers and fragrance, but don't want it to dominate the patio or balcony.

Containers are also ideal if you have soil problems, which may include compaction, clays or a high water table. In this case, container plantings not only are pretty but also may be the best choice for successful growing.

If you have any questions about growing conditions or types of plants for containers, please contact us at Flowers by the Sea Nursery. We have lots of ideas for you. Container gardens tend to grow like the conga line of water drops that the USGS described.  You plant pot#1, and it attracts pot #2, which attracts pot #3. You get the picture, and it's pretty. 

Updated 6/8/2017


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