Astilbes are easy to grow and maintain

There are few garden plants as easy to grow and as versatile as the astilbe, which is a hardy perennial.

While the flowers do exceptionally well in moist, shaded situations, over the years it has been discovered that many varieties can also tolerate full sun so long as they are well watered and not allowed to “bake.” This is also one of the few garden perennials that you can grow from seed or buy as plants.

A small package of seeds, and some patience, can result in more than 100 large plants of mixed colors and heights that will bloom in just about a year. For about $6 you can buy named and unnamed cultivars by mail and for $6 to $15 you can buy large, fully developed plants in the garden center. Not bad for an investment of a few bucks.

As a guideline, know that the more recent variety introductions will be the most expensive, and the most common will be the least expensive.

For gardeners on a budget, the astilbes are attractive not only for their inherent beauty, but the ease with which mature plants can be divided.

We grow our favorite cultivars in a cold frame to establish large plants in 2-gallon pots and then early each fall we cut each clump into at least four divisions. In my book, that’s a pretty good payback and a fast way to expand your plantings with little or no additional expense. Plants grown in the ground can be similarly divided and replanted early in the fall.

Astilbe, once referred to as false spirea, is closely related to

aruncus

and

filipendula

and the species is found throughout Asia. In the commercial trade, we find almost 150 varieties available ranging in size from just 6 inches to as tall as 4 feet. The colors range from white and pink to salmon, red and magenta.

Another, often overlooked charm of these plants is that they bloom over a long period of time, depending on cultivar and species. If you plan carefully you can have these plants blooming from late spring (

A. arendsii

) through late August (

A. taquetii

, also known as superba).

The plant, no matter what size or variety, has an open and airy growth habit that can soften the bold foliage of such plants as bergenia, rodgersia, pulmonaria, ligularia and hosta. Astilbes also complement fine-textured plants like ferns and bleeding hearts and are also used as inter-plantings in large beds of rhododendrons and azaleas.

While the perennial plants are not known for their colorful foliage—astilbe means without color—the cultivar known as sprite has many deep green, crinkly-edged, shiny leaflets. Its hybrid origin (as with most astilbe cultivars) go back to George Arends (as in

arendsii

) of Rondsdorf, Germany. He was responsible for the introduction of most of the astilbes grown today.

In 1911, Mr. Arends was attending a flower exhibit in London where he found

A. simplicifolia

and took it back to Rondsdorf. There, he began crossing it with a group of hybrids with shiny, dark, green compound leaves and white to pink gracefully arching plumes.

Much of the seed that you find today is derived from the original Arends’ crosses. We now know these by cultivar names such as alba, atrorosea, bronze elegans, elegans carnea, dunkellachs and rosea. From Arends’ original hybrids, newer selections such as Aphrodite, hennie graafland and sprite were introduced.

The Astilbe sprite is a mound-former with a fibrous root system that overwinters as a crown with many buds called eyes. Since this plant, and other astilbes, are not long-lived—approximately three to five years—the plants should be divided every three to four years to maintain vigorous growth. This division can be done in early fall or in early spring before the tight foliage in the crown begins to unfold. You may have a week to 10 days at most to do any spring dividing.

The division process is very simple. With a spade or digging fork, lift the plant out of the ground and shake any soil free of the roots. With a sharp knife—we use a machete—cut down through the crown leaving three or four “eyes” in each section.

Replant the divisions with adequate spacing at the same depth as they were formerly. The eyes should be about a half-inch below the soil line.

Do not fertilize, but keep the soil moist for several weeks to encourage root growth. If you are a biostimulant follower, you can use a product like Roots or PanaSea to water in the divisions.

It was once thought that astilbes could be grown only in cool, moist shade. But 25 years ago, some designers began to experiment and found that many of the varieties will do quite well in full sun so long as the roots are kept moist and somewhat cool.

This can easily be accomplished by keeping the crown and root zone mulched in the summer heat, thus keeping the underground portions of the plant much cooler. One fatal mistake, though, is to plant astilbes in a sunny location and then forget to keep them watered. The plants will expire quickly as evidenced by their crisp, baked foliage, a condition from which they never recover.

If you’d like to try growing astilbe from seed, Thompson & Morgan offers a dwarf and tall selection. Since you never know what colors are going to emerge, it’s a crapshoot. But once these plants mature, you can divide the best of the lot and simply make more of the ones you prefer.

If you’re looking for astilbes that break the mold, there are a few varieties such as Key West and Key Biscayne (you can find them at rootsrhizomes.com) that sport more colorful foliage and stems.

Another great asset of these plants is that they are virtually bug- and disease-free. In 20 years, I’ve only lost an astilbe because I divided it too late, but I’ve never had a disease problem.

In hot, dry summers, mites can be a minor problem that is easily controlled with strong sprays of water several times a week. It’s imperative to get the water under the foliage as well as on top of it.

Unfortunately, the late flowering taquetii types are prone to attacks from Japanese beetles, which will congregate and feed on the flowers. If left uncontrolled, the beetles will lay eggs in the soil around the base and crown of the plant and the resulting grubs may do damage to the crown and roots. At the first sign of the beetles, either remove them by hand or use an appropriate insecticide.

Some gardeners complain that they plant large beds of astilbe in a particular color scheme or design only to find several years later that the flower colors have mysteriously changed. It’s really not so much of a mystery though.

In these cases there may have been cross-hybridization of the plants during flowering season and the resulting seeds fall to the ground, germinate and produce an abundance of mixed colored offspring. The solution to this problem is to cut the flower stalks just after flowering so seed does not drop to the ground, which may also extend the life of the parent plant as well if seed production is avoided.

Astilbe can also be used as potted plants indoors as they force easily. Plant some crowns in late summer in 6-inch or larger pots and allow them to establish roots in the cold frame or sink the pots in the garden to the soil level.

The plants must receive about 90 days of sub-40 degree temperatures from November on. After 90 days, bring the pots into a cool indoor spot for a few days (or put in a greenhouse) and then move to a brighter location and begin to water and lightly fertilize. Flower spikes, which make good cuts when half open, will appear in four to eight weeks depending on the variety.

Keep growing.

Andrew Messinger has been a professional horticulturist for more than 30 years. He divides his time between homes and gardens in Southampton, Westchester and the Catskills. E-mail him at: Andrew@hamptongardener.com. The Hampton Gardener is a registered trademark.