What to Do with Agapanthus in September – 7 Jobs to Do Now for More Flowers Next Year

September is a turning point for agapanthus. After months of producing its spectacular globes of blue, purple, or white flowers, this sun-loving perennial is beginning to wind down for the season. But don't put away your gardening gloves just yet.

A little attention now can help agapanthus transition into fall and winter safely – and set the stage for healthy growth and abundant flowers next year. Whether you're familiar with the different agapanthus varieties or are learning to grow agapanthus for the first time, September is an important month to get your plants ready for the months ahead.

What you need to do in September depends largely on where you garden and which type of agapanthus you grow. In warmer parts of the US, plants may remain actively growing well into fall, while gardeners in colder USDA Hardiness Zones will need to start thinking about frost and winter protection. Here are the agapanthus jobs worth tackling this month.

1. Deadhead Spent Flowers

If your agapanthus has finished blooming, September is a good time to remove faded flower stalks. To deadhead agapanthus, use clean, sharp bypass pruners and cut each spent flower stem back to the base of the plant. Removing faded stems keeps the plant looking tidy and prevents it from putting unnecessary energy into seed production.

For this job, a lightweight pair of bypass pruners is all you need. The Fiskars 5/8-Inch Bypass Pruner, available at Amazon, is a practical choice for making clean cuts through green stems. Another option is the Fiskars 8-Inch Bypass Pruner, available at Walmart, which has a 5/8-inch cutting capacity.

However, you don't have to remove every spent flowerhead. The dried seedheads can add attractive structure to a fall garden, particularly when backlit by low autumn sunshine. If you enjoy the architectural look of agapanthus seedheads, leave a few in place and remove the rest.

2. Keep Watering – but Adjust Your Routine

Don't assume cooler September temperatures mean your agapanthus no longer needs water. If you're wondering how often to water agapanthus, it depends on your climate, rainfall, and whether the plant is in the ground or a container.

Container-grown plants can dry out quickly, particularly during a warm, dry fall. Check the soil regularly and water deeply when the top few inches have dried out, making sure excess water can drain freely. For controlled watering, the Ames 7-Pattern Garden Hose Nozzle Sprayer, available at The Home Depot, offers adjustable spray settings. For smaller pots, the Fiskars Indoor and More Watering Can, available at Walmart, makes precise watering easy.

Avoid keeping the soil constantly soggy. Agapanthus prefers well-drained soil, and excess moisture around the roots can become problematic as temperatures fall.

Gardeners in hot, dry regions may need to continue watering regularly, while those in cooler or wetter areas can gradually reduce the frequency.

3. Don't Cut Back Healthy Foliage Too Early

One of the easiest mistakes to make with agapanthus in fall is cutting the foliage down simply because flowering has finished. Instead, let the leaves continue to grow for as long as they remain green and healthy. Those leaves are still capturing energy that the plant can store in its roots for the following growing season. If you need to remove dead or damaged foliage later, a pair of Fiskars Steel Bypass Pruning Shears from Home Depot can make the job easier.

If you grow a deciduous variety, the foliage will naturally yellow and die back as temperatures fall. Once it has completely died back, you can remove it. Evergreen types retain their foliage and generally shouldn't be cut to the ground in fall.

4. Know Your USDA Hardiness Zone

September is an ideal time to check your agapanthus's cold hardiness before the first frost arrives. Agapanthus varies considerably in its tolerance of cold. Some varieties can survive winters in relatively mild climates, while others need significant protection – or are best grown in containers that can be moved indoors.

Your USDA Hardiness Zone is an important starting point, but it's also worth checking the specific hardiness information for your cultivar. If you garden in a colder zone, don't wait until the first freeze is forecast to decide what you're going to do. September is the time to make a winter-protection plan.

5. Start Preparing Container Plants for Winter

One of the advantages of growing agapanthus in containers is that you can move them to a more protected location when temperatures drop. If you need to winterize agapanthus because your variety isn't reliably hardy in your area, identify a suitable winter location now. Depending on your climate and the plant's hardiness, this could be a cool garage, greenhouse, porch, or another protected space. Don't move plants into a warm, dark room for the entire winter. A cool, bright location is generally preferable, particularly for evergreen types.

Before moving a container, check it for pests and disease, remove dead foliage, and make sure the pot has adequate drainage. Miracle-Gro Indoor Potting Mix from Amazon can be useful if a container needs fresh potting mix before being moved indoors. If the pot needs better drainage, Miracle-Gro Potting Mix is another practical container-gardening staple to have on hand when preparing plants for winter.

6. Protect Plants in Colder Climates

If your agapanthus is growing in the ground and you're in an area where winter temperatures regularly fall below its recommended hardiness range, September is the month to prepare to protect plants from frost. A layer of organic mulch around the plant can help insulate the roots when temperatures fall. Compost, shredded bark, or leaf mold are useful options. Vigoro Premium Wood Mulch from Home Depot is one option for creating a protective layer around the root zone.

Avoid burying the crown under a thick layer of wet material, however. Agapanthus needs good drainage, and prolonged cold and moisture can encourage rot. In particularly cold areas, gardeners may choose to grow less-hardy agapanthus in containers so they can be moved to shelter before winter.

7. Hold Off on Dividing Your Agapanthus

September can feel like a natural time to tackle overcrowded perennials, but resist the urge to divide plants now. Agapanthus generally benefits from being left undisturbed, and division is usually best carried out in spring as new growth begins. There's also no need to divide a healthy, flowering clump simply because it looks crowded. Agapanthus can produce impressive displays when grown as substantial clumps.

If your plant has completely filled its container, however, it may eventually need repotting. Choose a container only slightly larger than the existing one rather than dramatically increasing the pot size. A Self-Watering Planter from West Elm can be a practical choice when moving an established agapanthus into a slightly larger container.

September isn't about giving agapanthus a drastic haircut. Instead, think of it as a transition month: tidy the plant where necessary, keep the roots healthy, and prepare for the conditions your local winter is likely to bring.

Get those basics right now, and your agapanthus will have a much better chance of returning next year ready to produce the dramatic, globe-shaped blooms that make it such a standout in the summer garden.