Astilbe Doesn't Bloom Properly

by Bill
(Maple Valley WA)

I have grown Astilbe in the past, with good success. I recently moved and have cultivated a small shade garden. It is actually on the south side of my home, but gets plenty of shade, but I do have to water regularly. I have planted two Astilbe, one purchased from a nursery two years ago, the other from a hardware store garden center last year. Both plants appear healthy, with good foliage and multiple flower heads. The problem with BOTH plants is that the flower heads do not produce the feathery plumes I have always loved about this plant. The flower heads look normal in height, size, shape, etc. but simply do not open up completely (or even partially). They look like flower heads that have not completed the flowering process; that is, the stems of the flower remain knobby, bumpy clusters - never growing the individual, feathery flower petals.

I'm totally confused why both plants would exhibit this. I grow them with ferns, lobelia (cardinal flower), heleobores, and a few other species and everything thrives including the Astilbe (except for the flowering problem I have tried to explain).

Any ideas?

Thanks;

Bill

Doug says that it sounds like you have a major case of thrips on this plant. This is one of only problems an Astilbe ever develops (being a pretty cast-iron plant) but thrips do love it.

Thrips are very small (you'll seldom see this fly) and damage plants by sucking the juices out of them. This causes leaf mottling and flower abortion or damage.

Control is never perfect in the garden but a *combination* of things can quickly bring them under control.

Let me suggest an alternating (spray one product in week 1 - spray another in week 2 - go back to first product in week 3 continue to alternate)

Neem is good, permethrin products, insecticidal soap and rotentone work on this pest.

You'll also find that taking sky blue cards and coating them with tanglefoot (a horticultural glue that doesn't dry) and hanging them 6-12 inches away from the plants will catch an amazing number of them. Yellow sticky cards work well too but thrips seem to love blue cards better than yellow.

You may have lost the blooms this year but definitely get those controls going asap.

Good luck - let me know how it works out.