What to Do With Agapanthus in August to Boost Next Year's Blooms and Keep Plants Thriving

Agapanthus is one of the standout stars of the late-summer garden, producing elegant globe-shaped blooms in shades of blue, purple, and white just as many other perennials begin to fade. While these plants are still putting on a show in August, now is the perfect time to give them a little attention if you want an even better display next year.

Whether you're just learning how to grow agapanthus or already have established clumps in your yard, a few simple maintenance jobs this month will help extend flowering, strengthen the plant before dormancy, and encourage healthier growth for the season ahead. The same care applies whether your agapanthus is growing in the ground or in containers.

If you're inspired to expand your collection, now is also a great time to make a note of the best agapanthus varieties that have performed well in your area, so you can add new plants to your garden in spring or fall, depending on your USDA hardiness zone.

1. Deadhead Spent Flowers

One of the easiest August jobs is to deadhead agapanthus as the faded flower heads begin to finish blooming. Removing spent blooms helps the plant direct its energy into strengthening the roots rather than producing seeds, which can support healthier growth and better flowering next season.

Using clean, sharp pruners, cut each spent flower stem back to the base without damaging the surrounding foliage. A reliable pair of pruning shears, such as the Fiskars Bypass Pruning Shears, makes it easy to create clean cuts while protecting the plant.

If you'd like to collect seed or leave the decorative seed heads for late-season interest, allow a few blooms to mature naturally. For smaller trimming jobs and precise cuts, Fiskars Micro-Tip Pruning Snips, available from Amazon, are another handy tool to keep in your gardening kit.

2. Water During Hot, Dry Weather

Established agapanthus is fairly drought-tolerant once mature, but flowering plants still benefit from deep watering during extended periods of heat, especially across hotter parts of the U.S.

Water thoroughly when the top few inches of soil become dry rather than watering little and often. Deep watering encourages stronger root growth and helps support flowering through the hottest weeks of summer. Container-grown agapanthus will usually need more frequent watering than plants growing in garden beds, as pots dry out much more quickly.

Always allow excess water to drain freely to avoid waterlogged roots. For more consistent watering, a GARDENA AquaZoom Oscillating Sprinkler, available from Amazon, can help deliver even coverage across garden beds without creating areas of standing water, making it useful during prolonged dry spells.

3. Give It One Final Feeding

If you've been feeding your plants throughout the growing season, August is usually the last month to fertilize agapanthus before growth begins to slow. Giving your plants one final feed now helps replenish energy reserves while supporting healthy roots and next year's flowers. Apply a balanced fertilizer, or one slightly higher in potassium, to support flowering, then stop feeding by late August or early September. Continuing to fertilize into fall can encourage tender new growth that's more susceptible to cold damage.

A balanced granular feed such as Espoma Garden-Tone Organic Plant Food, available from Amazon, is a good choice for established agapanthus growing in borders, providing slow-release nutrients through the end of the growing season. If you're growing agapanthus in containers, Miracle-Gro Water Soluble Bloom Booster Flower Food is another great option, delivering a potassium-rich boost before it's time to stop feeding for the year.

4. Check for Pests and Diseases

Late summer is a good opportunity to inspect your plants for summer pests before the growing season comes to an end. Alongside common problems such as aphids and slugs, gardeners should also keep an eye out for agapanthus gall midge, a tiny pest whose larvae feed inside developing flower buds, causing them to become swollen, distorted, and fail to open. Look out for:

• Slugs and snails feeding on foliage
• Aphids gathering around flower stems
• Agapanthus gall midge causing distorted or unopened flower buds
• Yellowing leaves caused by poor drainage
• Signs of crown or root rot in consistently wet soil

Removing damaged growth and dealing with problems early will help keep plants healthy heading into fall. For slugs and snails, Sluggo Snail & Slug Killer, available from Amazon, is a popular pet-friendly bait for protecting ornamental plants. If aphids become a problem, Safer Brand Insect Killing Soap, available on Amazon, can be used on ornamental plants to control soft-bodied insects when applied according to the label directions.

5. Resist the Urge to Divide

If your agapanthus is looking crowded, it's usually best to wait before you divide plants. In much of the U.S., spring is the ideal time to divide evergreen agapanthus, while gardeners in warmer USDA Zones 8–11 may also divide deciduous varieties in early fall after flowering has finished.

Dividing during the heat of August can place unnecessary stress on the plant and reduce next year's flowering. Fortunately, agapanthus often blooms best when slightly root-bound, so frequent division isn't necessary unless the clump has become overcrowded or flowering has noticeably declined.

6. Prepare Container Plants for Cooler Weather

If you're growing agapanthus in containers, August is a good time to think ahead to winter protection. Gardeners in USDA Zones 8–11 can usually leave hardy agapanthus outdoors year-round. In colder regions, however, container-grown plants are more vulnerable because their roots aren't insulated by the surrounding soil, so plan to move pots into a sheltered garage, greenhouse, or other frost-free location before hard freezes arrive.

Checking containers now for good drainage and deciding where they'll overwinter makes the seasonal transition much easier. If moving large pots is likely to be a challenge, a plant caddy with locking wheels, such as the Bosmere Down Under Plant Caddie available from Amazon, can make it much easier to relocate heavy containers when colder weather arrives.

FAQs

Should I Cut Back Agapanthus in August?

Do not cut back agapanthus in August. Instead, deadhead spent flower stems as they fade, but leave the healthy foliage in place. The leaves continue to photosynthesize after flowering, storing energy in the roots that will fuel next year's blooms. Wait until the foliage naturally turns yellow or brown in fall before cutting it back, as removing green leaves too early can reduce flowering the following season.

Can I Plant Agapanthus in August?

In warmer parts of the U.S., container-grown agapanthus can be planted successfully in August if it's watered regularly while establishing. In colder regions, spring is generally a better planting time, giving roots several months to establish before winter.

With just a little attention in August, your agapanthus will finish the growing season in excellent health and store the energy it needs for another spectacular floral display next summer. Deadheading, watering wisely, and preparing plants for the changing seasons now are simple jobs that can make a noticeable difference when your agapanthus bursts back into bloom next year.