Once the threat of night frosts has passed, it’s time to plant your dahlias. If you plant the tubers in early May, you can enjoy the first blooms by early July. With this step-by-step guide, a summer full of vibrant dahlia flowers is just around the corner!
Dahlias, which bloom in late summer, are sensitive to frost. As a result, the tubers can only remain outside in the garden over the winter in mild regions with proper winter protection. The typical planting time for dahlias is in spring, once the risk of late frosts has passed. Be sure to plant them at the right depth: the tubers should be placed about five centimeters deep in the soil. After planting, gently press the soil down and water thoroughly.
If you insert a thin stake, about one meter long, into the planting hole when planting your dahlias, it can later support the heavy dahlia blooms. Be careful not to damage the freshly planted tubers. Tip: If you’ve had problems with voles in the past, plant the tubers in self-made wire mesh vole baskets for added protection.
Contents
Step-by-Step Guide: How to Plant Dahlias
Step 1: Check the Overwintered Dahlia Tubers
Remove the dahlia tubers from their frost-free storage (such as a box with dry potting soil) and inspect them. Remove any dried-out or rotting tubers. If you have old, dense tubers, reduce them to about four to five healthy tubers. Cut off the excess tubers at the old stem, as only the root collar has viable buds. Even individual tubers will sprout new dahlias after planting.
Step 2: Dig the Planting Hole
Use a spade to dig the planting hole. If you’re planting an entire bed, ensure there’s a distance of 50 to 80 centimeters between each tuber, depending on the variety’s growth habit. This spacing prevents the shoots from intertwining and ensures that the leaves can dry properly after rainfall.
Step 3: Add a Layer of Sand to the Bottom of the Hole
Dahlias are very sensitive to waterlogging. A layer of coarse sand at the bottom of the planting hole improves water drainage, especially in clayey soils.
Step 4: Place the Dahlia Tubers and Support Stake
Place the dahlia tuber into the hole before inserting the support stake. Be careful not to damage the tubers. For large-flowered, vigorous dahlia varieties, it’s a good idea to insert a stake into the planting hole at this stage and later secure the stems with a loose string. Without support, the heavy flower heads can easily fall apart.
Step 5: Cover the Dahlia Tubers with Soil
Plant the tubers at a depth where they are covered by about two to three finger widths of soil. The deeper you plant them, the lower the risk of frost in the fall. However, this will delay flowering. After planting, the old stem bases should still protrude slightly above the soil surface.
Step 6: Water Thoroughly
Finally, water the newly planted dahlias thoroughly. Important: If you plant your dahlias before the “Ice Saints” (late frost period), have winter fleece ready just in case a frost strikes overnight. The young shoots can be severely damaged by late frosts. For individual plants, you can simply place a black bucket over them at night as protection.
Pinching Young Dahlias for Bushier Growth
Dahlias grown from individual tubers often produce only a few shoots and narrow flower heads in the first year. To encourage a bushier growth habit, pinch the young shoots several times, removing the tips above a leaf pair. This delays blooming but promotes the growth of new shoots with flower buds from the axillary buds.
Frequently Asked Questions
When can dahlias be planted?
Even in regions with mild winters, it’s best not to plant dahlias before late April or early May. If they start sprouting before the “Ice Saints,” there’s a high risk of frost damage to the young shoots. If cold nights are predicted, protect the plants with winter fleece or a turned-over black bucket.
How deep should dahlias be planted?
Plant dahlias so that the root collar sits just below the surface, and the cut end of the old stem slightly sticks out of the soil. The shallower the planting, the earlier the dahlias will bloom.
Which way should dahlias be planted?
Place the dahlia tubers in the soil with the slightly curved root collar (where the old stem connects) facing upward.
What kind of soil do dahlias need?
Dahlias thrive in humus-rich, nutrient-dense soil that is also well-draining. If you have heavy, clayey soil, mix it with sand and potting soil to improve drainage and prevent waterlogging.
Can you start dahlias early indoors?
Yes, you can plant dahlia tubers in pots as early as March and grow them in a frost-free environment like a winter garden or greenhouse. Dahlias need plenty of light and should not be kept too warm, as this can cause the shoots to become leggy. You can also propagate dahlias through cuttings by breaking off young shoots and rooting them in an indoor propagation box. These plants will bloom in the same year. Transplant pre-grown dahlias into the garden only after the “Ice Saints,” and gradually acclimate them to full sunlight.
