How to Plant Flowers in an Old Fire Pit

Wood Ash

• Planting flowers on sites with large amounts of wood ash could present some challenges. Wood ash is a very fine powder, lacking the open structure that most plant roots need. It's also very alkaline and can contain heavy metals, depending on what kind of wood was burned. Only nonedible plants should be grown on old fire pits. Use a soil test kit to check whether alkalinity is below 8.0 before planting, and dig lots of peat, spagnum peat moss or other organic matter into unlined fire pits to help lower pH and add structure to the soil.

Drainage

• Brick or stone floors and walls can provide good drainage for plants and protect their roots from the poor soil surrounding fire pits. To check how well a pit drains, pour water into it until it's one quarter full, and time how long it takes to drain away. If it drains within five to 10 minutes, it's suitable for planting. Fill in the hole with a mixture containing 50 percent soil and 50 percent peat mix to the same level as the surrounding ground. Water it, and let it settle over two or three days, then top it up if necessary.

Planting

• Abnormal growth or yellowing leaves are signs that your flowers could be affected by wood ash. Wood ash deposits create high alkalinity, which prevents plant roots from absorbing iron and other minerals, and causes abnormal stems, flowers and leaves, and yellowing between the veins on leaves. Seedlings and young plants are most vulnerable to this problem, so don't use your fire pit to grow plants from seed, but plant the largest container-grown plants available at the nursery or garden center.

Flowers

• Grow fiery-flowered plants that tolerate high alkalinity to create a flowery blaze in your former fire pit. Garden phlox Lilac Flame (Phlox paniculata "Barten" Lilac Flame) grows in clumps 12 to 18 inches tall and 9 to 12 inches wide and bears lilac-purple summer flowers. Achillea Fireland (Achillea "Feuerland" Fireland) bears blood-red summer flowers and is suitable for the center of your bed, growing 30 to 36 inches tall and 18 to 24 inches wide. Both plants are hardy in U.S. Department of Agriculture plant hardiness zones 3 through 8. Day lily "Chicago Fire" (Hemerocallis "Chicago Fire"), hardy in USDA zones 3 through 9, grows to the same height as achillea Fireland and a little wider. This reliable plant bears green-throated red summer flowers.