How to Kill Agapanthus

Agapanthus (Agapanthus spp.) are fuss-free bulbs that feature rounded clusters of trumpet-shaped blue, purple or white flowers, but their vigor means they return every year and spread, even if you don't want them to. Growing in U.S. Department of Agriculture plant hardiness zones 6 through 10, agapanthus, also called lily of the Nile, grow in clumps 1 1/2 to 4 feet tall and 1 to 2 1/2 feet wide. You can dig the plants up to control agapanthus, or you can spray the plants with weedkiller.

Digging Up Bulbs

Agapanthus bulbs sprout new shoots every year, but you can control the plants by digging up the bulbs. The best time for digging up agapanthus bulbs is in fall or winter when the plants have stopped growing.

Step 1

Push a garden fork into the soil at one edge of the problem agapanthus patch.

Step 2

Lever the fork upward to lift the agapanthus bulbs out of the soil.

Step 3

Dig up the bulbs in the same way all over the patch.

Spreading Mulches

Mulches control agapanthus by blocking the light from the plants. A sheet of black plastic works best because it also reduces the water that reaches the plants and agapanthus shoots can't grow through it. Agapanthus is so strong growing it can penetrate loose mulches such as compost or shredded bark.

Step 1

Prune the agapanthus stems at soil level with pruning shears.

Step 2

Wipe the pruning shear blades with a cloth that was soaked in rubbing alcohol, which helps prevent pests and diseases from spreading.

Step 3

Spread a sheet of black plastic over the agapanthus plants.

Step 4

Place rocks on the edges of the black plastic sheet to weight it down.

Step 5

Leave the black plastic in place for one growing season. Pull out any agapanthus shoots that appear at the edges.

Spraying Weedkillers

Systemic herbicides, such as glyphosate, control agapanthus by moving through the plant to its bulbs. A ready-to-use 2 percent glyphosate herbicide controls agapanthus effectively.

Step 1

Put on long pants, a long-sleeved shirt, safety goggles and gloves. Choose a dry, still, dull day.

Step 2

Spray all agapanthus parts with the glyphosate herbicide.

Step 3

Spray any new shoots that appear later in the growing season when they are 6 inches long.