Potting Mix for Containers: What to Use on a Balcony

Use a bagged potting mix, not garden soil, in balcony containers. Garden soil compacts in a pot and drains poorly. A good mix is based on peat moss or coir with perlite or vermiculite, feels light and loose, and drains well. For a lighter pot, skip sand and topsoil, and read the bag label for volume and weight.

This guide is part of what to grow on a balcony.

Potting mix vs garden soil

Garden soil is the wrong filler for a balcony pot. Iowa State University Extension says garden soil alone is not a good growing medium, because it compacts in a container and that cuts drainage and aeration. University of Maryland Extension agrees that garden soils are too dense for containers and allows topsoil only in very large ones, at no more than 10% of the volume.

Iowa State does offer a homemade blend of equal volumes of garden soil, sphagnum peat and perlite. With no garden to dig, though, its own conclusion fits a balcony better: a commercial potting mix is often the best choice. It adds that cheap mixes can be heavy and drain poorly, while good ones are lightweight, well drained and resist compaction.

What goes into a potting mix

Potting mix ingredients vary by brand, but the same few appear on most bags. University of Maryland Extension lists peat, perlite, vermiculite, composted bark, compost and coir, often with a little lime and fertilizer.

Iowa State Extension describes the main ingredients:

The name on the bag tells you little. UMD says products labeled “potting soil”, “planting mix” and similar vary a great deal. It suggests avoiding sedge peat and any mix that feels heavy or gritty, has very fine particles or arrives in clumps.

Lighter potting mix for a balcony

A lighter potting mix starts with the ingredients. The University of Maryland Home and Garden Information Center, answering on Ask Extension, says many commercial mixes are based on peat moss, perlite and vermiculite, and calls this soilless media lightweight. It adds that sand is not necessary and tends to make containers much heavier and harder to move.

Wet mix still weighs far more than a dry bag, and no single weight fits every mix, because the ingredients differ. Check the bag label, which gives the volume and often the weight. Our guide to balcony weight limits shows how to add up a pot, its mix and the water, and who can tell you what your balcony carries. The pot itself matters less than the mix; lightweight planters compares the materials.

Volume tells you how much to buy. UMD says a 2-cubic-foot bag fills about three 5-gallon buckets or grow bags.

Potting mix for self-watering planters

Self-watering planters rely on the mix to draw water up from the reservoir. The Maryland answer on Ask Extension says a soilless mix of peat moss, perlite and vermiculite wicks well by itself, and that coir can stand in for peat. It also cautions that a wicking container might not work well enough in winter to keep roots hydrated.

Where the maker names a mix, follow the maker for that planter. Our self-watering planters guide quotes makers’ own instructions, which can be stricter than general advice.

No gravel in the bottom of the pot

Gravel in the base of a pot is not needed. Clemson Cooperative Extension says hanging baskets and window boxes need a lightweight soilless mix and drainage holes, with no pebbles in the bottom. Fill the whole container with mix and keep the holes clear. Our guide to planter saucers and drainage covers what goes underneath.

Reusing old potting mix

Old potting mix can often go back into pots. University of Maryland Extension suggests mixing used media half and half with fresh mix or compost, and not reusing mix from a plant that had root disease. Finished compost from a small bin can be part of that blend; see composting on a balcony.

For which crops need how much mix, see vegetables in containers, and for berries, strawberries in pots.