What can I put in my pots to help drainage?

Proper drainage is crucial for growing healthy plants in containers. Too much water left standing in a pot leads to root rot and other problems. There are several inexpensive and readily available ingredients you can add to potting mix to improve drainage.

Use perlite for aeration

One of the most common ingredients added to potting soil to help drainage is perlite. Perlite is a type of volcanic glass that has been expanded by heating. This process leaves perlite filled with tiny air pockets. When mixed into soil, these air pockets create more air space in the potting mix so water can drain through easily.

Perlite helps aerate the soil and prevents it from getting compacted down over time. It maintains the light, fluffy texture that roots need to spread and grow. Perlite also helps keep soil from staying overly wet after watering.

A good general recipe is to mix perlite and potting soil in a 1:1 or 1:2 ratio. For seed starting mixes, use up to a 1:1 perlite to soil ratio. For containers with established plants that don’t need quite as much drainage, a 1:2 or 1:3 perlite to soil ratio works well.

Try coarse sand for drainage

Another option to use in place of or along with perlite is coarse sand, also called builder’s sand. Look for sand labeled as “coarse” rather than fine or medium. You don’t want sand particles that are so small they compact the soil. Coarse sand maintains good aeration and drainage.

Coarse sand works especially well for succulents and cacti that require superior drainage. Mix a 1:1 ratio of coarse sand and regular potting soil for the best results with desert plants. Or simply amend potting mix with a cup or two of coarse sand per gallon of soil.

Mix in vermiculite for moisture retention

While perlite and coarse sand help free up excess moisture in containers, vermiculite offers a counterbalance by retaining water. Vermiculite is made from mica that has been exposed to high heat. This causes the mica to expand into accordion-shaped pieces full of crevices and channels. These channels hold onto water molecules while still maintaining spaces for air circulation.

Where perlite makes soil drainage better, vermiculite makes drainage more moderate. The water-retaining qualities of vermiculite can complement the benefits of perlite or sand. To use vermiculite in potting mix, try a ratio of 2 parts soil : 1 part vermiculite. Or mix equal parts vermiculite and perlite into soil to balance aeration and moisture retention.

Use compost to enrich soil

In addition to ingredients like perlite that keep soil loose, you can add compost to potting mix to increase drainage while also feeding plants. Garden compost, leaf mold compost, and even vermicompost made from worm castings make excellent additions to potting soil.

Compost offers nutrition in the form of slow-release organic matter and microorganisms that enrich the living ecosystem in the pot. At the same time, compost contains a diversity of particle sizes from decomposed materials that help maintain spaces for air and water flow.

To amend potting mix with compost, try mixing 20-30% compost into the potting soil. So for a 10 gallon batch of mix, add 2-3 gallons of compost. This ratio provides a good fertility boost while still allowing suitable aeration.

Try diatomaceous earth for a mild drainage boost

Another choice for amending potting mix is diatomaceous earth (DE). DE consists of fossilized remains of diatoms, tiny aquatic organisms. The skeletal particles of DE are extremely porous, providing added spaces for drainage and airflow when mixed into soil.

DE also has benefits as a mild natural pest control. The microscopic sharp edges of DE can abrade and cut the waxy outer layer of soft-bodied pests like aphids. For these benefits, mix a cup or two into each large bag of potting soil.

Use coffee grounds sparsely for pH balance

Coffee grounds can make a useful addition in smaller amounts to provide acidity and tie up excess salts. The grounds from brewed coffee are highly acidic with a pH around 4.5-5. When mixed sparingly into potting soil, the acidity helps counteract the high pH of alkaline water and fertilizers.

Coffee grounds also contain nitrogen, potassium, and other nutrients that gradually release into the soil. But avoid using more than 10-20% grounds in your mix, as too much can overwhelm plants and lead to overly acidic soil.

Mix in coconut coir for moisture retention

Another ingredient You can add to potting soil for improved moisture retention is coconut coir, also called coco coir or coco peat. This is made from the fibrous material found between the hard shell and meat of coconuts. The fibers are ground into a soft, spongy medium perfect for gardening.

Coconut coir absorbs water readily and holds onto it well. Unlike vermiculite, coconut coir provides excellent aeration and drainage too. It resists compacting down over time. Mixing in 10-30% coconut coir improves the moisture retention of regular potting soil while maintaining good drainage.

Use activated charcoal to prevent root rot

Activated charcoal makes another useful addition to potting mix, especially for plants prone to root rot. Activated charcoal absorbs toxins and other harmful compounds from soil through a process called adsorption. The porous structure of activated carbon traps contaminants, preventing them from reaching plant roots.

By keeping excess salts, fungi, and bacteria controlled in soil, activated carbon creates healthier growing conditions. Mix just a teaspoon or tablespoon per gallon of potting soil. Ensure thorough mixing so the benefits are distributed evenly.

Add pine bark fines for moisture control

Pine bark is a common ingredient in commercial potting soils for its excellent moisture management properties. While larger chunks of pine bark improve aeration, pine bark fines offer a balance of drainage and water retention.

Pine bark fines are made from small, decomposed pieces of pine bark under 1/4 inch in size. The particles absorb and slowly release moisture while resisting compaction. Blend about 30% pine bark fines into potting soil for raised garden beds, planter boxes, and large containers.

Use peat moss in moderation

Peat moss is a common additive used in commercial and homemade potting mixes. It has good moisture retention properties while remaining loose and aerated when dry. However, harvest of peat moss raises environmental concerns. Peat bogs are important, sensitive ecosystems that take thousands of years to form.

If you do use peat moss, limit the ratio to no more than 30% in your potting mix. Look for companies that harvest peat sustainably. Alternatives like coconut coir, pine bark, and compost work just as well while leaving peat bogs undisturbed.

Avoid soil from the ground

It may be tempting to dig up and use soil from your garden, but this is one additive to avoid in container mixes. Garden soil often doesn’t drain well and can contain harmful fungi, bacteria, pests, and weed seeds not suited to containers.

Potting mixes crafted with sterile ingredients and designed for container gardening provide the best results. Amend store-bought mixes with organic materials like compost to introduce helpful microbes while maintaining enough aeration.

Use straw or hay for large planters and raised beds

For very large planters and raised garden beds, lightweight additions like straw or hay improve drainage in the lower layers. Straw and hay resist compression and maintain air pockets for good drainage under the top soil layer.

Spread a layer of straw or hay several inches thick at the bottom of very large containers before filling in with soil. The hay helps excess moisture to drain out the bottom as needed. Just avoid using hay or straw in small pots where roots need more direct soil contact.

Conclusion

The key to keeping potting soil healthy is maintaining a balance of drainage, moisture retention, and aeration. Perlite, sand, compost, coir, and other amendments each help provide this balance in different ways. Test mixes with a range of additives to discover the perfect blend for your gardening containers and climate.