Container Garden Water-Saving Tips From a Soil Scientist

Over the last year or so I’ve noticed a lot of websites, blogs, etc. offering water-saving techniques for container gardening. Some tips are useful and scientifically sound, but some are just plain wrong. As a person with a Ph.D. in soil science (and a minor in water resources), this drives me crazy. Because of that, I wanted to put some tips out there that will actually work!

If you’re reading this blog post, it’s likely that you are a gardener that, like me, is either lazy or forgetful when it comes to watering. Despite my lack of a rigorous watering regime for my container plants, I still have a wide variety of beautiful specimens, mainly because I’ve found that these simple tips just plain work.

1. Pick the right plant

This is the biggest decision you’ll face for container gardening, and the best way to make it easy on yourself. Get to know your local landscape and floral supply store (a real one, not a department store gardening section). Workers there will likely have some good advice on what plants do well with very little water. I highly recommend sticking to “succulents“, which are generally adapted to dry climates with little rain. Some great examples are Aloe vera, Crassula ovata (Jade plant), Euphorbias,Schlumbergeras (Christmas cactus) and any other cactus species.

Succulents are generally “CAM” plants, meaning that they open their “stomata” (pores) at night instead of the day so that they can adsorb CO2 with minimal water loss (as opposed to opening stomata during the day like most other plants). Succulents also tend to have waxy skins that further limit water loss, and store lots of water inside their stout leaves or stems. Be sure to investigate the plant thoroughly before you buy it to see what it’s lighting, watering, and space needs are or might be once it matures.

2. Choose the right container

When it comes to containers you generally have two choices – terracotta (clay) pots and plastic containers. Both have advantages and disadvantages when it comes to limiting how frequently you will need to water your container plants.

The traditional terracotta clay pots are porous, meaning that water can, and does evaporate through the side of the pot, and not just through evaporation at the soil surface, or transpiration through the plant. This can be desirable for a few reasons. For one, the color of the pot will actually tell you how wet or dry the potting soil is, at that moment. The wetter the soil is, the darker the clay pot will be.  Some plants (succulent plants in particular) prefer moist but not wet conditions. Terracotta pots do a great job of preventing saturated soil in the bottom of the pot, which may damage plant roots. The downside of terracotta pots is that the plants will need to be watered more frequently than with plastic pots.

Plastic pots are not porous, so no evaporation occurs along the side of the pot. If you have plants that can tolerate wet conditions reasonably well, then using plastic pots is a great way to limit how frequently you need to water. If you don’t like the look of plastic pots, try placing the plastic pot on the inside of your container of choice.

3. Pick the right location for your pot

The less sun your plant is exposed to, the less water it will use. Shade reduces the temperature of the plant and soil, and thus the transpiration rates. Find out what sun/shade tolerances are of your plant of choice, and aim for something on the shadier side. Your plant may not grow as fast, but at least you won’t have to water it as much.

Also, try to place the plant in a location where you will see it everyday. This will make it more likely that you will notice that the plant(s) needs watering. More than once I’ve forgotten to water a plant that I don’t see everyday. Picking the right location is a great way to make sure that won’t happen.

4. Use mulch

Every single drop of water that you add to your container goes one of three places. It can be transpired through the plant, evaporated from the soil, or drained out the bottom of the pot. Adding mulch to the soil surface reduces how much water is evaporated from the soil. This is because the mulch shades the soil from the sun, which keeps the temperature down, and in turn reduces evaporation from the soil. One thing to keep in mind is that adding mulch is equivalent to adding a carbon-rich, nutrient-poor substance to the soil. This isn’t a problem, but be sure to add some fertilizer at the same time that you add mulch so that the plants don’t become nutrient-limited.

5. Don’t worry about the potting soil

There are a lot of gimmicky potting soils out there claiming to work miracles in terms of retaining water. Honestly, there’s not much difference between potting soils. I’d recommend just buying the potting soil that is the cheapest. If you follow the first four tips, then the type of potting soil you buy won’t make much of a difference. If you really want to go cheap, use topsoil from a corner of your back yard. It will work the same, as long as you lime and fertilize as needed.