Requirements for Self-Watering Soil

Growing Media

• The bulk of the potting soil isn't made up from actual soil, but from a soilless media. Equal parts of peat moss, compost and shredded bark resemble soil when combined but they provide better moisture absorption and don't compress inside the self-watering container. Commercial soilless mixtures also work well in the self-watering container, but avoid those that contain materials that trap moisture, as these materials absorb too much water too quickly from the irrigation reservoir.

Perlite

• Perlite adds aeration to the growing media. This mineral resembles small pieces of white foam. It makes the soil lighter, allowing more oxygen to penetrate to the plant roots. It also prevents the growing media from compacting, which can occur when the soil has constant access to moisture. Use 1 part perlite to every 6 parts growing media. Substitute coarse builder's sand or vermiculite if you don't have access to perlite. These items don't provide the superior aeration, but they still help combat soil compaction.

Dolomite Lime

• Tomatoes and peppers may suffer from a condition called blossom end rot in soils with the improper pH balance. Growing media that contains peat moss may be too acidic for the plants. Adding dolomitic lime to the soil before you plant ensures these plants remain healthy and productive in the self-watering planter. Use 1 tbsp. of lime for every gallon of potting soil. Plants that prefer a pH between 6.0 and 7.0, which include most vegetables and annual flowers, grow best with the lime addition.

Fertilizer

• Commercial growing media blends typically contain a slow-release fertilizer. Check the label for any fertilizer additions before adding more. The slow release fertilizer provides enough nutrients for the first three months of the growing season. Add a balanced slow release fertilizer to the growing media if the soil doesn't have fertilizer added or if you make your own growing media. Use the amount of fertilizer recommended on the label for the size of your self-watering container.