Making your own potting mixture makes sense when you have a lot of plants to take care of. It's cheaper than buying it pre-made at the garden store, and you have better control over the quality. You can also create custom mixes for specific plants. Most of the ingredients are available at garden or home improvement centers, but there are a few you'll need to create on your own where noted.
About Lightweight Potting Soils
Lightweight potting soils are best used for applications where you don't need the container to be heavy, as with hanging potted plants or indoor planters. Don't use a lighter potting soil for outdoor potted plants; they will blow over. For outdoor applications, use a soil containing coarse sand, which will help weight down the planters.
You can make any recipe lighter weight by replacing coarse sand with perlite. Perlite is a sterile compound created from volcanic components. It allows the soil to be more airy. Perlite is usually sold in bags or boxes alongside the potting soil at home improvement or garden centers.
Basic Lightweight Potting Soils
Mix your potting soil recipes in a wheelbarrow or whatever large mixing container you have on hand. You can use your hand, a hoe, or a trowel to these potting soils up. If you use your hands, wear garden gloves to prevent irritation and dryness.
A basic potting soil recipe is using 2 parts packaged potting soil to 1 part perlite. Mix this with 1 part peat moss or leaf mold. Add a slow release 14-14-14 fertilizer or bone meal, following the package directions for the amount of soil you begin with.
An even lighter-weight mix without soil can be achieved by taking 1 qt. of perlite, 1 qt. of vermiculite, and 8 qt. sphagnum peat moss and combining them. These ingredients, like the others, can be found at most garden centers. If your garden center does not carry them, ask if they can be ordered. Most garden centers are willing to place customer orders for no additional fee.
Specialized Lightweight Potting Soil Recipes
Some acid-loving plants, like azaleas or camellias, need a more acid-based potting soil. Make these plants happy by mixing 2 parts packaged potting soil, 2 parts perlite, 2 parts peat moss, 1 part leaf mold, and one-third part decomposed or composted manure. Leaf mold is a great nutrient. You may need to create the leaf mold and decomposed manure on your own in your composter, unless you can get it from a friend with a composter.
Bulbs, like tulips you're going to place indoors in a pot, enjoy 2 parts packaged potting soil, 1 part perlite, and 1 part peat moss or leaf mold mixed together, along with some bone meal added in the amount indicated on the package. The amount of bone meal needed depends on how much potting soil you're making.
Cacti prefer 2 parts packaged potting soil, 2 parts perlite, along with half part peat moss or leaf mold. You'll also need a package of bone meal and a package of limestone; follow the package directions to add the correct amount.