How do I improve drainage?
Many plants require excellent drainage for healthy growth. Plants are often grown on a slope or in a raised or mounded bed where irrigation or rainwater flows quickly away from plant crowns and roots.
Drainage can be enhanced by adding a combination of rock chips or grit of 3/8 " or less and coarse sand to your soil. We use 1/4"-10 gravel which has fewer fines that cause compaction. The addition of these large and uneven particles enhance drainage. The amount of amendments needed varies with your soil type. The goal is fast drainage and easily workable soil..
A rock chip mulch is generally used in the rock garden. This type of mulch allows water to drain quickly away from the crown of the plant, allowing the crown to dry quickly and reducing the risk of disease.
Raised beds can be filled with a mixture of sand, gravel and compost or bark dust to create a low fertility mix for growing alpines. We have used a combination of equal parts sand and gravel along with 10-30% compost for our raised beds with good results.