Basic Window-Box Mix
Use this moisture-retentive medium for most flowering annuals, perennials, and foliage plants.
2 gallons sphagnum peat moss
1 gallon perlite or horticultural vermiculite
1 gallon screened compost
2 tablespoons ground limestone (not hydrated lime)
Measuring with a bucket, mix in a wheelbarrow. Blend thoroughly, sprinkling with water to hold down dust. Add enough water to lightly moisten mix before using.
Variations
To avoid using peat, a crucial nonrenewable resource, substitute coir, the ground fibers of coconut husks. Use only 1 tbsp. ground limestone.
For plants that grow best in acidic soil, such as ferns, strawberries, and heather, leave out the ground limestone.
Window-Box Mix For Succulents
This fast-draining medium gives cacti, succulents, and herbs the extra porosity they need to prosper. Measuring with a bucket, mix
2 gallons perlite
1 gallon sphagnum peat moss
1 gallon screened compost
1 tablespoon ground limestone (not hydrated lime)
Measuring with a bucket, mix in a wheelbarrow. Blend thoroughly, sprinkling with water to hold down dust. Add enough water to lightly moisten mix before using.
Variations
Sand is too heavy to use in window boxes that will be hung from brackets, but in planters that will rest on a sill or ledge, especially in windy locations, a heavy potting mix lends extra stability. Substitute coarse sand or insoluble poultry grit for half of the perlite.