Astilbes, also known as false spirea, are fabulous, very showy, shade-loving perennial plants. They are easy to grow, and their fern-like foliage and pretty, plume-like flowers add long-lasting color to part shade borders where very few tall, colorful flowers will thrive. Virtually pest- and disease-free, they will continue to bloom for many years.
Although astilbe plants only bloom for about 2-3 weeks during summer, different varieties bloom at different times. The benefit for home gardeners is that by planting several species of astilbe that have a different blooming time you can extend your floral display to 2-3 months.
About Astilbe Plants
Astilbes are wonderfully shady characters. They grow in home gardens all over the U.S. adding color and character to shade gardens and shady areas.
Flower colors range from white to pink-red, deep red, violet, and soft lavender hues. The blooms also range in size from 6 inches to 2 feet.
Whatever the size, they make lovely cut flowers. But, if left in your garden, pollinators like butterflies and honey bees are going to have a field day!
What time of year does the astilbe plant bloom?
Astilbes are native to the east, specifically Japan, China, and Korea. There are at least 25 different species and 100s of hybrids.
Depending on the variety, astilbe plants will bloom from early summer until late in the season.
Cindy Haynes of the Department of Horticulture at Iowa State University’s Extension and Outreach program pinpoints specific months. Early blooming varieties generally start blooming in late May or June while late bloomers start in late July or early August.
One of the early blooming varieties that starts to shine in early summer is Peach Blossom. Introduced way back in 1903, Astilbes x Rosea is still available today.
Factors that affect astilbe blooming
It isn’t rocket science to realize that you need to know the best growing conditions for astilbe to ensure that they bloom. For example, this is a plant that will thrive in a shady area but not in full sun.
So, let’s look at optimum conditions for astilbe plants.
Astilbes need fertile, humus-rich soil that is consistently moist. But they don’t like heavy clay soils or any type of soil that is waterlogged.
They don’t like dry soils and they won’t do well in them. If the soil is too dry, astilbe leaves will get brown very quickly.
If your soil isn’t draining well, you may be able to improve it by adding peat moss or organic matter like compost. But do this before you plant astilbes.
Also, be aware that astilbe plants prefer soil that is slightly acidic. If you have a soil kit check the pH. It should be about 6.0.
When you grow astilbe plants you will quickly realize that they are tough. But, even though they can survive harsh winters, they will suffer in high temperatures unless they get lots of protection from the sun.
Even though they are shade-loving plants, astilbes do best in partial shade. While they won’t generally do well in full sun, they need a bit of sun to grow to their maximum size.
At the same time, they are more likely to do well in full shade than in a garden bed that gets full sun. If you are developing a shade garden, aim to incorporate established trees and bushes that will give natural shade to your perennials.
The golden rule is that astilbes like shade and they don’t like the sun. In terms of moisture, this means that the warmer it is, the more moisture they will need to survive.
Astilbe plants don’t handle drought at all. Their leaves will dry and go brown and eventually they will die.
If it gets very hot and dry, water your plants frequently. But if these are normal weather conditions, you probably shouldn’t be growing astilbes.
When to Plant
It’s important to plant your astilbes at the right time. If you plant in the heat of summer, they probably won’t survive, let alone flower!
Wherever you are, the best time to plant is in spring or in the fall. Also, remember that they are quite slow-growing plants, and it takes a little while for them to become established. Once they are, you’ll find they are wonderfully low maintenance.
Astilbes aren’t very needy but they do need phosphorus to bloom. For this reason, it’s a good idea to use a fertilizer that contains phosphorus.
Use a 5-10-5 or 10-10-10 product and sprinkle fertilizer on the soil around the plants once they are in the ground. When they are established you can fertilize again in early spring each year.
How long do astilbe plants bloom?
Depending on the variety of astilbe you plant you will have flowers in your garden anytime from late spring until late summer. The different varieties also offer a wide range of colors in terms of both foliage and flowers.
Depending on the variety you choose to plant, your astilbes will bloom in late spring, mid-summer, late-summer, and early in the fall. So, if you plant a whole bunch of different varieties, your astilbe plants will bloom for as long as 2-3 months.
But no one variety is going to keep going for more than 2-3 weeks.
How do you get astilbe to bloom?
We have discussed the factors that affect astilbe plants blooming. If you follow these basic rules, it’s unlikely that your astilbes won’t bloom.
But, if they get too much sun, your astilbe leaves are likely to burn. And, if they don’t get enough sun, they aren’t going to bloom the way you want them to.
If the soil is dry they are unlikely to bloom. But, if you ensure they have rich soil and add lots of organic matter, then you are very likely to be rewarded with flowers.
Also, astilbes do best in mass plantings where they don’t have to compete with the roots of shrubs and trees.
Why are my astilbe plants not blooming?
First look at whether you are growing your astilbe plants in the right conditions. Apart from the soil, temperature, moisture, and so on, you also need to be sure that your climatic conditions are suitable.
As Cornell University points out, they will do best in USDA Plant Hardiness Zones 4-9. But, even if they are damaged by late spring frosts, they usually rebound and recover very quickly. They are, after all, shade-loving plants.
Even though they will grow in very shaded areas, they need a bit of filtered sunlight to bloom. Ideally, they should be in shady locations that get early morning or late afternoon sun.
Another factor that might be stopping your plants from blooming is moisture. Even if you’ve got the soil right, if water pools around the roots, this could be the baddie!
What to do if your astilbe plant doesn’t bloom
If your astilbes aren’t flowering you can take steps to make them bloom. Because they are perennial plants that live for many years, you have a big advantage.
You can adjust the soil, by adding more compost to ensure it doesn’t get waterlogged. You can also add fertilizer to ensure that your plants get the nutrients that they need to flower.
When you water your plants, make sure that you focus your hose pipe at the base of the plant. This will help to avoid the risk of mildew that might develop if the leaves get too wet.
Even if your astilbe plants haven’t flowered the way that you hoped they would follow a sensible maintenance program. Cut back dead blooms and keep the plants looking neat and tidy.
In the fall, cut the plants back to about 2-3 inches off of the ground. Cover the area where they are growing with mulch to protect them.
Chances are that your plants will regrow their foliage in spring when the air and soil temperatures warm up. And, if you’ve got all the other requirements right, they will bloom.
Give them the right nutrients in early spring and split them every 3-5 years to keep them healthy. That way they will definitely keep blooming.
Astilbes aren’t difficult plants. They are incredibly easy to grow and maintain in the right environment.
If you’re looking for a dependable perennial plant that will grow well and flower in a shady area in your garden, this is certainly one to consider. By planting a whole lot of different varieties, you can have a shade garden full of astilbes that will flower for up to 3 months throughout the summer.
We’ve provided you with lots of tips and advice about growing astilbes. But, the chances are that you want to grow other shade-loving plants in your shade garden. If so, here’s where to look for a lot more advice.
Mix a few of these together and you’ll have your very own shady symphony.