Making your own potting soil mixtures from separate components can be less expensive than purchasing commercial potting soils already mixed. You can also design the potting soil with the exact right of nutrients and water-drainage abilities for your specific plants. When you're making any kind of potting soil recipe, you'll want to use sterilized garden soil that doesn't contain any weed seeds, fungal spores or bacteria. To sterilize garden soil or "loam," sift the soil through a 1/4-inch mesh sieve onto a baking tray. Spread aluminum foil over the soil and put the tray into the oven. Bake the soil at 180 degrees Fahrenheit until the soil reaches the same temperature.
Standard Potting Soil Mixes
For a standard potting soil recipe that works well for most flowers, palms and other houseplants, combine 2 parts loam with 1 part sharp sand, 1 part humus (leaf mold) and 1/2 part dried cow manure. For each bushel (8 gallons) of the mixture, mix in enough bone meal to fill a 5-inch-wide planter pot. Another good all-purpose potting soil recipe is a mixture of 7 parts sterilized loam, 3 parts peat moss and 2 parts sharp sand, with 4 oz. of balanced granular fertilizer (10-10-10 or 14-14-14 NPK) and 3/4 oz. of ground limestone or chalk per bushel of potting soil mixture.
Humus-Rich Potting Soil Recipe
For plants that demand more humus than what's contained in the standard potting soil recipe, such as ferns, primulas and begonias, you can make a modified mixture. Mix together 2 parts each of sharp sand, loam and humus. Mix in 1/2 part dried or composted cow manure. Add one 5-inch-wide planter pot's worth of bone meal to each bushel of the potting soil mixture.
Woody Plant Mix
Woody or hardwood plants, such as daphnes and azaleas, have their own specific potting soil requirements. Combine 2 parts loam, 2 parts peat moss, 2 parts sharp sand, 1 part humus and 1/3 part composted cow manure.
Cacti and Succulent Potting Soil Recipe
Most cacti and succulent plants have similar potting soil requirements, mainly that the potting mixture needs to be extremely well draining. Mix together 2 parts loam, 2 parts sharp sand, 1 part of small broken-up pieces of a clay flower pot and 1/2 part humus. For each bushel of this mixture, mix in a 5-inch-wide flower pot's worth of bone meal and another of ground limestone.
Soilless Potting Mix Recipes
A soilless seed-starting mix can be as basic as 1/2 part vermiculite mixed with 1/2 part peat. Another easy yet effective seed-starting recipe is 4 parts peat, 2 parts perlite and 2 parts vermiculite. For orchids, combine 6 parts fir bark, 1 part peat moss and 1 part medium-grade charcoal.
Seed Starting and Cutting Mixes
For starting seeds, combine 2 parts sterilized loam, 1 part peat moss and 1 part sharp sand. Strain the peat and loam through a 3/8-inch mesh sieve for best results. To each bushel of potting mixture, add 1 to 2 oz. of superphosphate, 1/2 oz. of potassium nitrate and 4 to 6 oz. of ground limestone. Unlike many seed-starting recipes, cutting mixes are almost always soilless. For cuttings, combine 3 parts perlite, 2 parts coarse-grade peat and 1 part coarse or sharp sand. Or, for an easy soilless recipe for cuttings, combine equal parts peat and sharp sand. If you start your cuttings in sand, you can transfer them after they root into a mixture of 1 part loam, 1 part humus or peat moss and 2 parts sharp sand. When you're ready to transplant your seedlings or rooted cuttings, use a potting soil mixture containing 2 parts sharp sand, 1 part loam and 1 part humus.