Astilbe flowers should be propagated every 3 or 4 years to maintain healthy plants and promote new growth of blooms and flowers. You can also propagate astilbe flowers at other times if you simply want to create more plants. Properly propagating astilbe flowers is not very difficult and anyone can do it. So, here is a handy how-to guide on how to properly propagate astilbe flowers
Step 1 - Know When to Divide and Propagate
It is usually best to propagate astilbe flowers in the late fall after blooms have died or in early spring before astilbe flowers and plants have grown enough to produce blooms and flowers. When propagating astilbe flowers, you don't need the top parts of the plant so much as you do the crown, stem and root ball. So, even dividing and propagating astilbe plants that are only 2 to 4 inches in height is acceptable and will work just fine.
Step 2 - Dig Out the Astilbe Plant
Use your small garden spade to carefully dig around the astilbe plants to be removed and divided. Make sure to begin digging around the approximate drip line of the astilbe plant as this will probably be the point to where roots have extended to. After you dig out the astilbe plant, gently remove it and carefully remove any loose dirt or soil clinging to the root ball.
Step 3 - Divide the Astilbe Plant
Use your fingers to gently pull apart the crown section and root ball of the astilbe plant. Divide the root ball in quarters if possible. Alternatively, you could use a small pair of scissors for this task.
Step 4 – Choose a New Location
Choose shaded areas to plant your new astilbe divisions. Astilbes will grow better in shaded areas and don't do so well and direct sunlight.
Step 5 - Prepare the Soil
Turn the soil in the new location with a good all-purpose fertilizer that has a high nitrogen content. Also add a light application of supers phosphate or animal manure to the soil.
Step 6 - Plant the Divisions
Dig holes that are the same depth as used for the original astilbe plants and insert your new divisions in the holes. Pack soil around the new divisions tight enough to keep the plants upright but not so tight as to damage the crown or stem. Also make sure to space your new divisions about 16 to 30 inches apart
Step 7 - Add Organic Mulch
Add 2 or 3 inches of organic mulch around the area of for your new divisions. Make sure to allow enough room around this stems to allow the new divisions to grow properly.
Step 8 - Apply Fertilizer
Apply more all-purpose fertilizer in your new division planning area.
Step 9 - Water the Astilbe Transplants
Thoroughly water the new astilbe transplants, but make sure not to soak the soil too much. Add water in increments and allow the water to soak in to the soil before adding more.