How to Improve Drainage in Pots, With or Without Repotting

How to Improve Drainage in Potted Plants

To improve drainage in a pot, make sure water has a way out and that the potting mix lets it get there. Clear or add drainage holes, raise the pot 1 to 2 inches off the ground, empty the saucer after every watering, and use a mix opened up with perlite or pine bark. Do not add gravel to the bottom. Most of these steps work on a planted pot without disturbing the roots.

The right fix depends on where the water is getting stuck, so water the pot once and watch what happens:

1. If nothing comes out the bottom, the pot has no holes or the holes are blocked.
2. If water drains but the saucer stays full, the pot is sitting in its own runoff.
3. If water races through while the mix stays dry, the mix has dried out and shrunk away from the pot wall.
4. If the surface stays wet for days, the mix is dense and old, or the plant is being watered too often.
5. If the roots form a solid mass, the plant has run out of room.

Each of these has its own remedy below. The symptoms of a pot that drains badly are easy to mistake for thirst. University of Maryland Extension lists wilting or yellowing of the lower and inner leaves as the primary sign of excess moisture, and our guide to container plants wilting in wet soil covers how to tell the two apart.

What to Use for Drainage in Pots

Drainage comes from the mix itself and from the holes, so the useful materials are the ones blended through the whole pot. The ones layered at the bottom do nothing or cause harm.

Material	How to use it	Effect on drainage
Perlite	Mixed through the potting mix	Improves it
Pine bark	Mixed through the potting mix	Improves it; large particles add air
Coarse sand	Mixed in at almost 50 percent by volume	Helps only at that high rate
Window screen, coffee filter, paper towel	One layer over large holes	Neutral; keeps the mix from falling out
One pot shard	Laid across the hole	Neutral; keeps the mix in
Gravel, rocks, a layer of shards	Layered at the bottom	Makes it worse
Garden soil	Used in place of potting mix	Makes it worse; too dense for air and water to move

North Carolina State Extension describes perlite as heat-treated volcanic rock used to improve drainage, and pine bark as a large-particle ingredient that is good for aeration. One example mix from the same handbook is 60 percent pine bark, 20 percent peat and 20 percent sand. Sand has a reputation as a drainage aid that it does not earn in small amounts: the mix has to be almost 50 percent sand before it drains quickly. For the differences between the white granules and the tan flakes on the shelf, see perlite versus vermiculite.

Why Gravel in the Bottom Makes Drainage Worse

Water does not move easily from a fine material into a coarse one. It stays in the potting mix until the mix just above the gravel is saturated, and only then does it drip through. A Washington State University Extension review traces that finding to soil science work done nearly 100 years ago, and notes that the coarser the bottom layer, the harder it is for water to cross into it.

The wet zone that collects at the base of the mix is called a perched water table. A gravel layer does not remove it. It lifts it closer to the roots and takes away soil depth, and University of Missouri specialists point out that a deeper column of mix drains better than a shallow one. Maryland, NC State and Clemson all give the same instruction: no rocks, gravel or layer of shards under the mix. We go through the evidence in more detail in rocks in the bottom of a pot.

How to Add Drainage to a Pot

Every container needs holes or slits that let excess water out. If yours has none, add them. NC State calls drilling a hole or holes in the bottom the best thing to do with a pot that lacks them. Holes do not have to go through the base: the same handbook notes that they can be placed along the side of the container, 1/4 to 1/2 inch from the bottom.

On a planted pot, check the existing holes before drilling. Roots and settled mix can plug them. Tip the pot and push a pencil or skewer up through each hole until water runs.

If a decorative pot cannot be drilled, double pot. Keep the plant in a plain container with holes and set it inside the decorative one. Lift it out to water, or tip out what collects afterward. NC State warns that a pot left touching its drained water can absorb it back into the mix, where it may burn the roots.

Then give the water somewhere to go. To help with drainage, Maryland Extension suggests bricks or scrap lumber, or the ceramic and plastic pot feet sold at garden centers, which raise a container an inch or two off the ground. Empty saucers regularly so the collected water does not encourage root rot.

Improve Soil Drainage in Pots Without Repotting

When the holes are open and the pot still stays wet, the mix is the problem. Potting mix breaks down with age into finer particles, and fine particles hold more water and less air. You can refresh part of it in place. Clemson’s advice for plants in containers too large to repot is topdressing: remove the top 2 or 3 inches of soil and replace it with fresh mix every other year or so. Use a mix with visible perlite or bark so the new layer stays open.

A pot that sheds water has the opposite fault. When mix dries far enough to pull away from the sides of the pot, water runs down the gap and out the bottom while the root ball stays dry, and it looks like fast drainage. University of Illinois Extension recommends immersing the container in a bucket or sink of water and leaving it to absorb water through the holes in the bottom. Our walkthrough on bottom watering houseplants shows the method.

Watering habits finish the job. Water thoroughly, so the whole root ball is moistened and excess drips from the holes, and then wait. NC State’s test is to push a finger 2 to 3 inches into the mix and water only if it is dry at that depth. For a large container, Maryland suggests inserting a dowel long enough to reach the bottom of the pot, which shows whether the lower half is still wet when the surface looks dry.

When Repotting Is the Real Fix

Some pots cannot be corrected from the top. Clemson lists the signs: roots in a solid mass around the root ball, roots growing out of the drainage hole, or a plant that wilts shortly after watering. Move it to a pot 1 or 2 inches larger in diameter, and do it in spring or summer while the plant is actively growing. Fast-growing plants may need this every year, and slow growers every two to three years.

Roots that are brown and soft, with an odor, are beginning to rot. That plant needs fresh mix and a clean pot, and the root rot recovery guide covers the steps. When you do repot, place a single piece of broken pot or a square of screen over the hole and fill the rest with mix. Old mix from outdoor vegetable containers can be stretched by blending it 50:50 with fresh mix or compost. Our article on reusing old potting soil explains when that is safe.