Container Gardening Drainage

Container Gardening Drainage: Get the Best tips on drainage for your container garden and find out why it's one of the most important but over-looked steps when gardening in this style.

Practically every page, or article, I write concerning container gardening, I always include a tip on container gardening drainage.  Read more on choosing the correct size of container.

One of the easiest things to do is to forget to add drainage holes, or to under-estimate the amount needed.

In the following, you'll learn what to look for, and what to add if it's not there so that drainage will be at it's prime.

Is adding material to a container before adding soil really necessary?? Click Here.

container gardening drainage

First step-Container Gardening Drainage

When planning a container garden, the first step you should take is to look at what drain holes are present. While most store bought planters will have a hole or several holes present, many are insufficient.

Container Gardening Drainage Tip

If you have a planter that keeps moist soil for long periods of time, check your drainage. Roots that are allowed to set in water will rot quickly!!

If they're there, great! No work is to be done!.

I like to see around 6 to 8, 3/8" drainage holes in the bottom of a 14" planter. The bigger the planter, add more. The smaller the planter, add less. A planter with only one drainage hole has a larger risk of clogging than a planter with numerous small holes.

If extra drainage or any drainage needs to be added, here's what I would do. Grab a power drill and a drill bit that's suited for what material you'll be drilling into (wood, plastic, concrete, etc.). For Example: Don't try to use a wood bit for a concrete planter. It won't work!!!

Then simply add the amount of holes necessary for good drainage.

The Extra Mile

Since the potting mix can clog up the drainage holes and prevent the water from leaving the pot, an extra step to ensure water drains properly, is to add material to the bottom of the planter before adding soil.

Over the years, I've read numerous ideas on what to add to accomplish this. Here are just a few that are tried and true:

*Take a piece of broken terra cotta pot and place it over the drainage holes for better Container Gardening Drainage. This prevents the potting soil from clogging up the hole.

*To aide in Container Gardening Drainage, I've read of gardeners using packing peanuts to add to the bottom of the container, then adding there soil. This as well, will make for an extremely lightweight container.

*You can also add coarse sand or fine gravel in the bottom of the planter.

As with any of the additives mentioned, a good step to finish off this plan, is to add a small layer of rock or gravel before adding your potting mix.

Are you wondering if all this is too much? Is any of it even necessary?? Here's a short, interesting article that is well worth the read.

Container Gardening Drainage: The Myth

This is just one of those myths that refuses to die, regardless of solid scientific evidence to the contrary! Nearly every book or web site on container gardening recommends placing coarse material at the bottom of containers for drainage. The materials most often recommended for this practice are sand, gravel, pebbles, and pot shards. Other ‘benefits' often mentioned include preventing creatures from entering through the drain holes, and stabilizing the container.

Some of these recommendations are quite specific and scientific sounding. Consider this advice from a 1960's book on container plants: "Adequate drainage is secured by covering the hole in the bottom of the pot with a piece of broken flowerpot, concave side down; this in turn is covered with a layer (1/2" to 1" deep) of flowerpot chips. On top of this, a 1/4" to 3/8" layer of coarse organic material, such as flaky leaf mold, is placed."

The advice seems to make perfect sense, and it's presented so precisely. After all, we know that plants need good drainage so their roots receive adequate oxygen, and we also know that water passes through coarsely textured material faster than it does fine material. So what's not to like?

The Reality Nearly 100 years ago, soil scientists demonstrated that water does not move easily from layers of finer textured materials to layers of more coarse textured. Since then, similar studies have produced the same results. Additionally, one study found that more moisture was retained in the soil underlain by gravel than that underlain by sand.

Therefore, the coarser the underlying material, the more difficult it is for water to move across the interface. Imagine what happens in a container lined with pot shards! Some of my previous columns have mentioned soil interfaces and their inhibition of water movement. We can see the same phenomenon occurring here: gravitational water will not move from a finely soil texture into a coarser material until the finer soil is saturated.

Since the stated goal for using coarse material in the bottoms of containers is to "keep soil from getting water logged," it is ironic that adding this material will induce the very state it is intended to prevent.

The Bottom Line:

  • Planting containers must have drainage holes for root aeration.
  • "Drainage material" added to containers will only hinder water movement.
  • Use good topsoil throughout in perennial container plantings for optimal water conditions and soil structure.

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Myth Article Used With Permission and Written By: Linda Chalker-Scott
Associate Professor and Extension Urban Horticulturist
WSU Puyallup Research and Extension Center 2606 W. Pioneer Puyallup, WA 98371Phone: (253) 445-4542
Web page: The Informed Blog: Garden