In this video, This Old House landscape contractor Roger Cook shares tips for successfully growing flowers in stubborn clay soil.
Steps for planting in clay soil:
1. Use a garden fork and rotary tiller to break up the clay soil within the planting bed.
2. Spread an even layer of expanded shale over the soil, then till in the shale to a depth of 6 to 8 inches.
3. Cover the tilled bed with a thick layer of compost. Use a garden rake to evenly spread out the compost.
4. Till the compost 4 inches into the soil.
5. To create a dry riverbed, lay out a garden hose in the shape of the riverbed. The hose will represent the centerline of the riverbed.
6. Rake out from the centerline 12 inches in both directions, creating a 4-inch-deep x 24-inch-wide riverbed.
7. Line the entire length of the excavated riverbed with fabric soil separator.
8. Set larger rocks into the soil along both edges of the riverbed, then fill the center of the riverbed with smaller river rocks.
9. Use a garden trowel to dig a hole 1 inch wider and ½ inch shallower than the plant's root ball. Set plant in the hole and backfill with soil.
10. If any of the potted plants are root bound, use the blade of the garden trowel to slice through the matted roots around the outside of the root ball and across the bottom.
11. After planting all the plants, cover the entire flowerbed with 2 inches of hardwood mulch. Be careful not to pile the mulch up against the plants.
12. Water immediately and then regularly for at least one year.