What To Do With Asters in September – 4 Easy Tasks

I have known asters to keep flowering right through November in the wet gardens of Wales. Just as the days become noticeably shorter and much of the summer garden begins to fade, their bright pops of pink, purple and lilac can light up a border. For me, few perennials are quite so valuable at this point in the gardening year.

The trouble, of course, is that fall weather isn’t always gentle. Some asters can produce stems four or five feet tall, topped with masses of daisy-like blooms. Add a heavy downpour and a gust of wind and, without support, that magnificent display can quickly end up horizontal. So, when caring for asters in September, staking and supporting taller plants is one job I wouldn’t neglect.

Fortunately, knowing how to grow and care for asters is relatively straightforward, and a little attention now can keep plants flowering for weeks to come. There are plenty of varieties to choose from, but I have a particular soft spot for New England asters, native to North America, with their vivid late-season blooms. ‘Purple Dome’ New England aster is available to order now via Nature Hills, and is a good compact option. Here are four simple jobs that will help to keep asters in good form this September.

1. Watering

Asters should be in full flower at this point in the year, and prolonged dry spells can quickly take their toll, particularly on plants added to your yard this year.

As with most perennial plants, I prefer to water asters deeply and less frequently, rather than giving them a light sprinkle every day that only wets the surface of the soil. Direct your watering can or hose towards the soil at the base of the plant, avoiding the foliage where possible. Try this extendable garden hose from Walmart.

When watering, keep the leaves dry to reduce the risk of powdery mildew, something asters can be particularly susceptible to (more on that later).

Established asters growing in the ground should need considerably less attention as temperatures fall, so always check the soil before reaching for the watering can.

Pots, however, will dry out surprisingly quickly, particularly during a warm September, so check these every few days and water whenever the top inch or so of soil feels dry.

2. Support

New England aster "Rudelsburg" Michaelmas daisies Asters

Many asters are surprisingly tall plants, with some varieties reaching four or five feet by the time they flower in August and September. Unfortunately, September is also when heavy rain and strong winds can arrive, and a top-heavy plant covered in blooms can quickly be flattened.

I usually stake taller perennials in spring. By late summer, the foliage has hidden the support almost completely. But if your asters are already beginning to lean, it isn’t too late to intervene.

Push a few bamboo canes or hazel rods into the ground around the clump and loosely secure the stems with garden twine. Avoid tying everything together too tightly – asters look far better when they retain their natural, slightly loose shape (albeit with a little support).

Alternatively, these metal plant supports from Amazon are a simple option for asters and other perennials.

3. Deadhead

Asters can flower for months, and a little deadheading in August and September will help to keep plants looking their best.

Once individual blooms begin to turn brown and fade, use clean garden snips to remove them, cutting back to a healthy leaf or side shoot. Try these Spear & Jackson pruning shears, available from Target.

Every few days, remove spent blooms – the ones that are obviously past their best. Not only does this tidy the plant, but it can encourage remaining buds to develop rather than allowing energy to go into producing seed.

If you don’t have time to deadhead, however, don’t worry. Your asters will survive perfectly well without it; think of this as a useful bit of TLC when caring for asters in September, rather than an essential job.

4. Check for Mildew

Beautiful late summer flowering Aster flowers also known as Symphyotrichum or Michaelmass Daisy

Powdery mildew is one of the more common problems with asters, and by September you might notice a dusty white or gray tint to some leaves. While it can look worrisome, a small amount late in the season is not something to lose sleep over.

Prevention is usually better than cure. Make sure there is plenty of airflow between clumps and water the base rather than the foliage. If only a few leaves are badly affected, snip these off and dispose of them in your green waste.

For asters that suffer badly year after year, overcrowding might be part of the problem. Once flowering has finished, consider dividing congested clumps in fall to give plants a little more room to breathe.

What to Shop

For more seasonal inspiration, check out our guide on how to grow coneflowers, with tips on keeping these perennials in good shape through to November.

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