In northern climates, you can plant New England asters from spring to early fall, and they should become established before winter. In southern climates, it’s best to plant them only in the spring and fall because hot summer temperatures can be damaging to a plant that isn’t yet established. Asters are fast growers and will typically bloom in their first year.
Light
New England asters need full sun to grow and bloom their best. That means their growing site should get at least six to eight hours of sunlight on most days.
Soil
These plants prefer rich soil with a slightly acidic soil pH and good drainage, but they can grow in other soil types as well. They’re even tolerant of clay soil.
Water
New England asters like moist soil. They can tolerate lower levels of soil moisture if the soil is not completely dry to the touch. Water your plants well during periods with little to no rainfall.
Temperature and Humidity
New England asters tend to grow vigorously throughout the climates of their USDA hardiness zones 4 to 8. Extremely hot weather can make the plants wilt, but they should come back once the temperature cools. Humidity generally isn’t an issue, though ensure that your asters have good air circulation when planting them. Poor airflow plus high humidity can be a breeding ground for diseases.
Fertilizer
Plan to fertilize your asters in the spring when new growth appears. Use a water-soluble or granular fertilizer that is formulated for flowering plants. Choose a fertilizer that is higher in phosphorus than it is nitrogen or potassium. For the amount to use, follow the product label instructions. You also can enrich the soil with compost.
Types of New England Aster
Many New England aster varietieslook the same but have different flower colors. Some of these include:
‘Harrington’s Pink’: Rose-pink flowers‘September Ruby’: Ruby-rose flowers‘Alma Potschke’: Reddish-pink flowers‘Purple Dome’: Violet flowers‘Barr’s Blue’: Violet-blue flowers
Pruning
In early summer, pinching back stems every few weeks can promote a bushier and more compact growth habit. However, stop the pinching process by August, or you might accidentally take off some flower buds. If your asters become very tall and lanky, you might need to stake them to prevent the stems from flopping over. Cut the asters to the ground after they’re done flowering and the foliage dies in the fall. If you’re not too concerned about garden tidiness, consider leaving the foliage intact to protect overwintering insects and small animals.
Propagating New England Aster
New England aster can be propagated easily by division, cuttings, or seeds. Many gardeners find that division is the safer route because it’s impossible to know for sure what the aster will look like when it is propagated from seed. To propagate from division, wait until the aster plant is at least three years old. This ensures a robust root system to easily divide without damaging the main plant. Or, propagate New England aster by cuttings:
How to Grow New England Aster From Seed
Though asters will readily self-seed in the garden, it’s possible to collect the puffball-like seeds and germinate them indoors during the early winter. Sow seeds in well-draining potting soil and cover them with plastic for added humidity. They should germinate with a soil temperature of 65 to 75 degrees Fahrenheit.
Potting and Repotting New England Aster
When potting asters, choose a pot that is a little bigger than the aster plant. The pot should have a drainage hole. Plant the aster in well-blended compost, in a hole a little larger and deeper than the pot the aster was originally in. Cut back the plant after flowering and overwinter it in a cold frame or greenhouse. If the aster becomes root-bound, transfer it to a pot that is a few inches wider than the current one.
Overwintering
To help asters thrive, water the ground well before the first freeze hits. After the ground freezes, cut the asters back to the soil level and cover them with 2-3 inches of mulch. If you’re not too concerned about garden tidiness, consider leaving the foliage intact to protect overwintering insects and small animals.
Common Plant Diseases
Asters are generally hardy flowers, but they can be susceptible to powdery mildew. This is a fungal disease that leaves patches of white or gray powder on the leaves and stems of an infected plant. Check the undersides of leaves, as this is where it often first appears. In addition to the white or gray patches, the plant also might yellow, look withered, and lose leaves. To treat powdery mildew, you can apply a fungicide formulated to treat the disease. It’s also recommended to prune off infected portions of the plant, especially if it’s only on a small area and hasn’t spread yet. Prevention is key as well. To avoid powdery mildew problems with your asters, make sure there is good airflow among the plants. Thin your asters by dividing them every few years in the early spring or fall. Also, always water plants at their bases not from above. Wet foliage encourages fungal diseases; fungi does not grow on dry foliage.
How to Get New England Aster to Bloom
If your New England aster isn’t blooming, check the particular cultivar you have and make sure you are looking for blooms at the right time. If the plant is supposed to be in bloom but there are still no signs of flowers, consider the age of the plant. Very young plants are still trying to establish a strong root system and thus might not devote energy to flowers for the first season or two. Finally, consider the fertilizer. Asters don’t need much feeding, and they can easily have received too much nitrogen from a typical fertilizer. That nitrogen can lead to lovely foliage but no blooms. Reduce the fertilizer and always use one with low nitrogen and high phosphorus to see if that sparks a profusion of color.
Common Problems with New England Aster
A problem that can affect aster plants is called aster yellows. Despite the name, this can happen to other plants as well. It presents itself with stunted growth, the plant sending out secondary shoots, smaller and narrower leaves, and a twisted look to the leaves, as though they are drying up despite ample water. The colors of the plant will be off as well - the typical lovely colors will be severely muted, and the leaves will be a paler color than usual. Flowers might be very small or malformed. The aster won’t produce any seed. This problem is caused by the aster leafhopper, an insect that spreads a particular bacterium from one plant to another. The result is damage to the whole garden, but especially to the aster plants. Unfortunately, there is no treatment, and the best you can do is remove the affected plants immediately to prevent the bacterium from spreading further.
