I'm guessing it's a matter of soil content. But what exactly I wouldn't know. Maybe you do.
It's not always soil pH. Here are more reasons:
https://www.gardeningknowhow.com/ornamental/flowers/flower-color-change.htm
They are in partial shade
Browning flowers is common after transplanting. I would cut them off. Continue with best care tips below.
https://www.gardeningknowhow.com/ornamental/flowers/astilbe/astilbe-is-turning-brown.htm
https://www.gardeningknowhow.com/ornamental/flowers/astilbe/growing-astilbe-plants.htm
I want to transplant two struggling astilbe plants into pots. What kind of pot is best? Terracotta? Plastic? Ceramic? And then how best/where to winter-over? Or is it better for the plants to be in nursery pots and "disguise" with decorative outer pots? I have a wine barrel 1/2 into which I was thinking of transplanting 2-3 astilbe - bottom of barrel will have several large drainage holes. Thoughts? Thank you!! ~heidi
If they are struggling it may be due to amount of light or soil that is not well draining. Be sure to use potting soil in the containers, not garden soil. It never hurts to add some perlite to the potting mix to aid drainage.
You can use any of the options you mentioned for the container but terra cotta doesn't do so well over winter. If you use a decorative outer pot, be sure to remove the inner pot when watering or water will build up in the bottom, even if there are holes in the outer pot.
They are hardy to zone 4, some to 3, so you can leave them outside during the winter in your zone 6. However, make sure they are mulched well and I would also move them to a protected area of the yard.
https://www.gardeningknowhow.com/ornamental/flowers/astilbe/growing-astilbe-in-pots.htm
Hi. I bought a new Astilbe plant this year and planted in my front garden that faces east with morning sun. I live in Cochrane and we have a lot of clay in the soil. We added compost horse manure to our clay and when I planted the Astilbe, we added bone meal into the hole w water. The plant was doing really well until all of the rain that we had. Now the plants looks like it is partly surviving. It has brown leaves that are very dry. We added peat moss to the base of the plant hoping it helps it. Can you please help me save this plant? When it was blossoming, it was beautiful.
It could be overwatered from the rain and the clay soil, which doesn't drain well. Or, it could be the plant is getting too much sun. Usually, just about an hour of sun is enough. You might consider moving it to a shadier location with moist, rich soil.
https://www.gardeningknowhow.com/ornamental/flowers/astilbe/growing-astilbe-plants.htm
Is October the wrong month to buy an astilbe for a container on the north balcony ? Should it be protected from the cold winter ? New apartment..lots of space…no plants yet….any OTHER suggestions ?
You may want to wait till spring to plant perennials in containers. That would give them a summer to get well established before the next winter. Then when you are ready to buy, get plants that are hardy in two zones colder than you are. That will help protect them in winter. Plants in containers don't have much insulation unless you wrap them for winter.
If you want to add some green during winter, consider adding some evergreens in containers. Most are very hardy and shouldn't be a problem during winter. Here are some ideas:
https://www.gardeningknowhow.com/special/containers/evergreens-for-containers.htm
https://www.gardeningknowhow.com/ornamental/shrubs/flowering-shrubs-in-pots.htm
https://www.gardeningknowhow.com/ornamental/trees/japanese-maple/japanese-maples-in-containers.htm