Homemade potting soil

Before the arrival of specially blended potting mixes, gardeners used to create their own homemade potting soil, using a variety of ingredients, some store-bought, some not. In many cases, these recipes were closely held secrets.

These days there are so many packaged products available that there's really no reason to bother mixing your own. Why devote the time and effort to mix your own when somebody else has already done it for you? Well, because it's fun---that's why!

Most homemade potting mixes contain two or more of the following: milled sphagnum peat moss, the key ingredient in all good potting mixes because of its ability to absorb and retain water; vermiculite, the mineral mica that's been heated and puffed (it too holds water well); perlite, an inert material that doesn't absorb water but makes mixes lighter and faster draining; and compost, an important source of slow-release nutrients and micro organisms. In some cases they may also contain nutrients from a variety of organic sources.

If you're going to sow seeds in flats, consider making soil less potting mix, one that's lighter and less dense than potting soil and capable of absorbing water well but draining quickly. These mixes need not contain any nutrients because from the time they germinate until they develop their first true set of leaves, young seedlings get all the nutrients they need from the seeds themselves.

The simplest recipe calls for mixing 1 part sphagnum peat moss with 1 part vermiculite. Some gardeners sow seeds in straight vermiculite, and that's fine too. Once seedlings develop their first true set of leaves, it's time to pot them and give them a different growing medium, one that contains some nutrients.

For this mix, combine 1 part sphagnum peat moss with 1 part vermiculite, and add 2 parts sifted compost. The compost provides texture and nutrients, which is why fertilizers aren't needed. Instead, feed young transplants each time you water with a weak solution of liquid seaweed.

For container-grown ornamental and vegetable plants, the mix should include 1 part sphagnum peat moss, 1 part perlite and 3 parts sifted compost. This mix works  well for those who garden on balconies or rooftops because it's relatively light. Perlite can be a bit costly, though, so if weight isn't a consideration, substitute coarse sand.

To 1 gallon of mix, add 2 tablespoons each of blood meal, bone meal and gypsum and 6 tablespoons of greensand. This combination of goodies provides all the nutrients plants need to grow and will last for months. The diet can also be supplemented with compost tea of liquid seaweed at each watering.

Vary the ingredients in this mix to address the specific needs of plants. For instance, for a plant that requires extra-rich soil, double the amount of compost. If the plant requires acidic soil, double the peat moss. For cacti or succulents that prefer drier conditions, skip the perlite altogether and double the amount of sand.

If you can't water as often as you should, add some water-absorbing polymer crystals to your mix. These inert, nontoxic crystals increase the water-holding capacity of the mix by absorbing, then slowly releasing water as the mix dries.