How Many Drainage Holes Does a Planter Need?

Why drainage holes matter

The job of a drainage hole is simple: let excess water escape after you water. The Old Farmer's Almanac puts it directly: "A container should have a drainage hole or some other way to allow water to pass through it. Water-logged soil promotes bacterial and fungal growth, which will stunt plants' progress." Without drainage, every watering adds water that has nowhere to go, and the root zone stays soggy.

A pot without drainage can still work if you use it as a cachepot and keep the plant in an inner pot that drains. But as a permanent home for a plant, a planter with open holes is the safer choice. For more on how drainage layers interact with holes, see this article.

How many holes does a planter need?

There is no fixed number that works for every pot. The right count depends on the volume of soil and the material of the planter. A simple starting point: small pots up to about 6 inches in diameter often do fine with one or two holes. Medium pots from 8 to 12 inches usually need two to four. Large planters 16 inches and up benefit from four or more.

These numbers are starting points, not rules set in stone. If you use a dense potting mix that holds water, lean toward more holes. If you use a coarse, fast-draining mix, fewer holes can be enough. For small pots, see our best 6-inch planters; for medium pots, see best 12-inch planters.

• Small pots up to 6 inches: 1 to 2 holes.
• Medium pots 8 to 12 inches: 2 to 4 holes.
• Large pots 16 to 24 inches: 4 to 6 holes.
• Extra-large planters 30 inches and up: 6 or more holes, or a central drainage grid.

Drainage hole size

Hole size matters as much as count. Holes must be large enough to pass water quickly but small enough to keep potting mix inside. If the holes are too small, fine particles clog them. If they are too large, soil washes out with every watering. You can prevent soil loss by placing a piece of landscape fabric, a coffee filter, or a mesh screen over the holes, a trick that also works when you want bigger holes for faster drainage.

As a starting point, a hole that lets a pencil pass is about right for a small pot; large planters do better with openings roughly the size of a coin or larger. For large planters, some makers use a single central opening plus a raised inner base or a drainage grid. That keeps water from pooling while supporting the soil. See planter drainage hole size and planter drainage hole spacing for more detail.

Position and spacing

Drainage holes belong in the base of the planter, not up the sides. Holes in the side of a pot do not drain the lowest layer of soil, which is exactly the layer that gets waterlogged. The best way to drain a pot cleanly is to put one or more holes in the flat base, and to space them evenly across the area. That lets water move through the whole root ball instead of draining one side only.

If the planter has a raised inner base, the holes should sit in the recessed area where water collects. Some makers put one large center hole; others put several smaller holes around it. Spacing them evenly helps the whole root ball drain. Read more in planter drainage hole position and planter drainage hole spacing.

How the material changes the calculation

The planter's material changes how much drainage the holes need to provide. Unglazed terracotta is porous: water can evaporate through the walls, so the soil loses moisture even without a single hole. Because of that, a terracotta pot can get away with fewer holes. But the same porosity means it dries out faster, which is useful for some plants and a problem for others. See the best terracotta planters guide for details.

Non-porous materials do not let water out through the walls. Plastic, glazed ceramic, resin, fiberglass, and metal all hold water inside, so the drainage holes are the only escape. These planters need a more generous hole count. Suncast, for example, manufactures its outdoor products in the USA using domestically sourced resin, and resin planters rely entirely on their base holes. Austram, another maker, offers decorative garden planters in several finishes, and in each case the base drainage design is what keeps the soil from staying soggy. For non-porous options, see the best plastic planters.

Checking a planter before you buy

When you pick a planter, flip it over. Look at the number, size, and position of the holes. If the planter has no holes, you can still use it as a cachepot: put a drained inner pot inside and empty the outer pot after watering. If the planter has holes but you are worried about soil loss, add a screen.

If you already own a planter with too few holes, you can often drill extra holes in plastic, resin, fiberglass, and wood. Ceramic and terracotta can be drilled with a masonry bit, though there is a higher risk of cracking. For planters that come with good drainage from the start, browse the best drainage hole planters roundup.

What to pick for your use

Questions

Can a planter have too many drainage holes?

In theory, yes. Too many big holes can let soil wash out and dry the root ball quickly. In practice, most planters have too few holes rather than too many. As long as you keep soil from escaping through a screen, a generous set of holes usually drains better. That said, a planter meant for a reservoir-style self-watering system should not have open holes, because the reservoir holds water.

What if your planter has no drainage holes?

Use it as a cachepot. Place a pot that has good drainage inside, and empty any water that collects in the outer pot after each watering. This is common with decorative ceramic and metal pots. You could also drill holes, but that may damage the finish or cause cracking.

How big should drainage holes be?

Big enough to let water flow freely within a few seconds, small enough to hold the soil. A hole that lets a pencil pass is about right for a small pot; large planters do better with openings roughly the size of a coin or larger. If soil washes out, add a screen.

Should drainage holes be in the center or around the edge?

Both work as long as water can drain from the lowest point of the base. If the planter has a raised inner base, the holes should sit in the recessed area where water collects. Some makers put one large center hole; others put several smaller holes around it. Spacing them evenly helps the whole root ball drain, which is one reason to check the planter drainage hole position article.

Do self-watering planters need drainage holes?

Most do not, because they use a water reservoir and wicking action instead of free drainage. Some have an overflow hole at the level of the reservoir so excess water can escape without flooding the soil. If you want a self-watering planter, choose one designed for that purpose rather than adding holes to a regular pot. See the best self-watering planters guide.

Can you add extra drainage holes?

Yes, in many materials. Plastic, resin, fiberglass, and wood can be drilled with a standard power drill. Ceramic and terracotta can be drilled with a masonry bit, though there is a higher risk of cracking. Always turn the pot upside down and drill from the outside in, and support the base so it does not flex.