Tuesday, September 8, 2009

Astilbe Glitters In The Shade

Astilbe is a genus of easy-to-grow, herbaceous perennials native to China, Japan and North America, with frothy blooms and fern-like foliage. The name Astilbe (pronounced a-STIL-bee) is formed from two Greek words meaning "without glittering", referring to the leaf surface that is often dull. I think the name is unfortunate for Astilbe flowers do seem to glitter in the summer shade garden. Astilbe is commonly known as false spirea, goat's beard and false goats beard.

Bloom season ranges from early to mid-summer. Flower colors include shades of red and pink, lilac to purple, and white. Plant height ranges from 8" to 48".

Though there are about 18 species within the genus, there are very many cultivars and hybrids, so astilbe is a great subject for the plant collector who wishes to specialize in a particular genus. Astilbe, however, works well with companion plants such as ferns, hostas, azaleas and rhododendrons, pieris, kalmia. As summer wears on, astilbe tends to wear out, so it is a good idea to plant with companions that are more attractive later in the growing season.

Astilbe performs well in USDA climate zones 3 through 8. Because it is native to woodland coves and ravines, it stands to reason that shade is the preferred environment. But astilbe also thrives in sunny gardens if adequate moisture is supplied. Slightly moist, loamy soil with pH ranging from 5.6 to 7.5 is recommended. Take care not to over-water.

Astilbe plants are most commonly available in 3-1/2" to 4" pots, 1-gallon pots, or as bare root plants. I should note at this point that bare root plants are usually divisions, and they are not at all attractive. They may lack foliage. Fibrous roots extending from the main rhizome usually look dry. Depending on the number of growing points (known as "eyes") per division, the length of the rhizomes could be from 2" to 6". Container-grown plants acquired in late summer don't look too good, either, but don't let that stop you. It is simply the nature of the beast.

Before planting, take a soil sample to your local Cooperative Extension Service office. For a small fee, they can run a lab test and tell you what your soil may need.

Prepare the planting bed by cultivating at least 12" deep, removing all traces of weeds. Composted manure and peat moss may be incorporated into the soil. If you choose to use synthetic fertilizer, incorporate 10-10-10 fertilizer at a rate of no more 3 lbs. per 100 square feet into the top 8" of soil. Avoid synthetic fertilizers contacting any part of your plants.

Space at 12" to 18" apart. Dig planting holes into the cultivated soil a little less deep than the depth of the growing container. Water the plants in their pots. Place the plants into the holes and back-fill, watering as you go. Press soil around the roots. Do not cover the top of the root mass with soil. The tops should be slightly exposed.

If planting bare root divisions, plant approximately 4" deep and cover with a good grade of organic peat soil. Water gently to avoid disturbance.

Add a top-dressing of mulch around the plants, not on top of them, about 2" deep. The mulch helps retain soil moisture, so you can water less frequently. It also helps suppress weeds.

Astilbe foliage lends a lush, woodsy appearance to the landscape while the frothy flower clusters add beauty and color. Diseases are seldom a problem. Insects, deer and rabbits don't seem interested. So, astilbe ranks high on my list of recommended plants.

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