Potting & Soil Mixes

Potting Soil: What It Is and How to Choose One

Scroll for more →

Potting soil is a growing medium made for containers. It is not dirt dug from the ground. Most bags have no true soil at all. They blend peat moss or coco coir with bark, compost, perlite or vermiculite. The mix should drain well and leave air around roots.

Why potting soil is different from garden soil

Garden soil belongs in open ground. Water can spread through a bed, and soil life helps keep it loose. The same soil acts in a new way inside a pot. It packs down under its own weight and drains slowly. It may also bring in weed seeds, pests or plant disease.

Potting soil uses light, open parts to solve that problem. They resist packing down, let spare water leave and keep air near the roots.

What's actually in the bag

Most potting soil blends combine a few core ingredients:

• Peat moss or coco coir - forms the base and holds water.
• Bark, compost or other plant matter - adds shape and may add some plant food.
• Perlite or vermiculite - creates air gaps and changes how water moves through the mix.

Each brand uses its own ratio. A moisture-control mix may use more peat or coir. A cactus blend often has more perlite or other coarse pieces. Read the bag rather than relying on the product name.

General-purpose vs. specialty mixes

An all-purpose mix works for many houseplants and vegetables in pots. Some plants need a special blend or a change to the base mix:

• Succulents and cacti need fast drainage. Add perlite, pumice or coarse sand.
• Orchids often grow in bark or sphagnum moss instead of fine potting soil.
• Seedlings need a light, fine mix with few large bark pieces.

A bagged all-purpose potting soil is a sound starting point when the plant has no special soil need.

Signs a mix is working well

A few checks tell you whether potting soil is doing its job in a given pot:

• Water should sink in and leave through the drain hole. It should not sit on top for many minutes.
• Dry mix should still feel loose and a little springy. It should not form a hard mass.
• Healthy roots are often firm and white to tan. Brown, soft roots can point to soil that stays wet for too long.

When to replace it

Plant matter in the mix breaks down over time. After one or two years, the soil may pack tight and lose air gaps. It may also hold water in a new way. Fresh mix can restore its form. A fast-growing plant in a small pot may need a change sooner.

What to avoid

• Garden soil or topsoil - it is too dense for most pots and can carry pests or disease.
• An old, wet bag - heavy clumps or a sour smell can mean the mix took on water.
• The wrong special blend - wet soil is a poor fit for a succulent. A very dry cactus mix is a poor fit for a fern.

How much potting soil you actually need

Bags are sold by volume, such as quarts, cubic feet or liters. A 10-inch pot takes about a gallon of mix. A large five-gallon pot needs several times that amount. Buy a little extra if you are not sure. Dry leftovers keep well in a sealed bag.

Potting soil for specific popular plants

A few common cases are worth calling out beyond the general vs. specialty split above:

• Pothos, philodendron and monstera often suit an all-purpose mix. Add perlite if it dries too slowly.
• African violets and other fine-rooted plants tend to suit a light, fine mix rather than large bark chunks.
• Herbs in pots need a mix much like one used for vegetables. Most common herbs do not like wet roots.

Storing unused potting soil

Potting soil does not spoil like food. It can lose some plant food as it ages, though. Damp storage can also cause mold and hard clumps. Seal an open bag and keep it dry and out of direct sun. Check old soil for a musty smell or clear mold before use.

Bottom line

Potting soil is made for containers, not dug from a yard. A blend with peat or coir, plant matter and a drain aid suits many houseplants. Succulents and orchids need a mix that fits their roots. See well-draining potting soil for drainage help. The soilless potting soil guide explains why most bags contain no true soil.