How to Grow and Care for Asters

It's a cruel trick of Mother Nature that the most glorious weather of the gardening season coincides with the decline of most blooming plants. Asters (Symphyotrichum spp.), however, don't play along with the prank. Like garden mums, asters flower in response to the shortening days of fall, giving gardeners a beautiful display of buds that can bloom from August through October. Native to North America, New World asters comprise many species in several different genera of plants, as well as dozens of cultivars, but for gardeners, asters are simply great flowers that provide purple or blue daisy-like flowers late in the season.

Although home and garden centers often market asters as a seasonal purchase among displays of pumpkins and hay bales, asters are long-lived perennials that can become a permanent part of your landscape. These fast-growing perennials will be ready to put on a good fall display in their first year, and once established, they will hold their own for many years.

Aster Care

While you can grow aster flowers from seeds planted in the springtime, it may take several years for them to mature into full-sized plants. More often, asters are planted from potted nursery specimens. They do best in loamy, well-draining soil, and desire a good amount of space around the plants to allow room for their roots to expand.

Every three years or so, the root clumps should be dug up and divided to keep the plants from getting too woody and dying out in the centers. The woody center can be discarded, with the outer portions replanted at the same depth as before.

Light

Plant aster flowers in an area that boasts full sun for the majority of the day. Too much shade can cause lanky plants and fewer flowers, especially for the more common cultivars and hybrids. There are some native species varieties, however, that will do quite well in partially shady conditions.

Soil

Asters appreciate loamy soil that's slightly acidic, with a pH ranging from 5.8 to 6.5. If your soil is alkaline, you can correct it by adding organic matter such as well-rotted manure, leaf mold, or compost.

Water

Keep new plantings moist and continue watering regularly until the flowers are finished blooming. As a rule of thumb, the soil your asters reside in should stay consistently moist but never saturated. One thing to note: Try to water the base of your asters without splashing water on the leaves—doing so can cause mildew or fungal growth. One inch of rain or watering once a week is usually recommended for most perennial plants.

Temperature and Humidity

Aster flowers thrive in cooler temperatures and are frost-hardy, able to withstand near-freezing temperatures temporarily. When it comes to humidity, asters have no special preferences and therefore will not need increased humidity levels or extra spritzing.

Fertilizer

Asters are moderate feeders, and they appreciate being fed with a balanced flower fertilizer twice a month, beginning in spring and continuing until the blooms begin to open. Excessive nutrients can shorten the blooming time, so stop fertilizing asters in August.

Types of Asters

The taxonomy of asters is somewhat complicated, as it now includes several genera of plants, all within the Asteraceae family. Most gardeners do not need to worry too much about the taxonomical details, as all these plants are sold as asters and all have the familiar daisy-like flowers and perform the same way in the garden. Some of the more popular cultivars include:

• 'Celeste': These dark blue flowers bloom early and feature bright yellow centers.
• 'Hazy': Another early bloomer, the "hazy" aster boasts raspberry-pink flowers with yellow centers.
• 'Puff': The puff aster is hardier than many other white cultivars and will bloom among the earliest.

Pruning

Pruning asters is simple: pinch off the dying flowers to make room for new growth. Remove dead or wilting stems promptly. For the simplest pruning, cut the flowers when they are almost in full bloom and bring them inside to enjoy in a vase.

When frost finally kills off the foliage, clip off the stems at ground level. This can also be done in the spring to allow birds to feed on the flower seeds throughout winter—both finches and chickadees are especially fond of aster seeds.

Propagating Asters

Asters can be propagated by collecting seeds or rooting stem cuttings, but by far the easiest and recommended way is propagation by division. Asters will survive no matter when you perform the division, but if done in late fall or early the following spring, the plants will become established enough to put on a fall display in their first year.

1. Dig up the root clump with a shovel.
2. Divide the clump into smaller pieces for replanting. Aster roots are tough, so you will need to use a sharp spade for that. Discard the woody center portion of the clump.
3. Replant the pieces at the same depth as the original plant. Water thoroughly immediately after replanting and keep the plants moist until you see new growth. Feed the divisions with bone meal (follow the label for amounts), which is high in phosphorus and helps the plants get established.

How to Grow Asters From Seed

While asters can be grown from seed, germination can be difficult. Depending upon the variety, you might also wind up with something that looks nothing like the parent plant. For those reasons, propagating from division is the recommended route.

Overwintering

When autumn rolls around and the asters stop blooming, give them a good amount of water - about 1 to 2 inches - a few weeks before the first freeze. Cut down the foliage after that frost (or let the asters stand until spring so wildlife can enjoy them). Cover the asters with a few inches of mulch to protect the roots during the winter period.

Common Pests and Plant Diseases

Rust and powdery mildew disease can affect aster foliage. Follow proper plant spacing recommendations to improve air circulation and avoid splashing water to prevent these problems.

Most insect pests leave asters alone, but lace bugs can be a bother. You're more likely to notice the damage they cause than the insects themselves, which are very small and a nondescript grayish-brown color. If you spot yellowing foliage and leaf drop in the summer, consider using insect soap on the plants, coating all sides of the foliage to impact the hiding pests. Fortunately, lace bug outbreaks precede aster blooming time, so spraying won't affect butterflies and bees.

How to Get Asters to Bloom

Though asters often bloom readily with simple care, there are a few things to look for if your asters aren't performing as they should. They need about 1 inch of water per week, so keep an eye on the forecast to make sure they get enough from mother nature. Stake tall varieties to keep them from falling over and ensure they get the full sun they require. Work in some compost to boost blooms, and don't hesitate to pinch the flowers back in spring and summer to encourage even more of them.