The Q&A Archives: Digging and Dividing Dahlias

Question: This past summer, I grew dahlias (the large variety) and had pretty good success with them. However, as the summer got later, the stems (at the top) seemed to get thinner and wouldn't support the new blooms so they just flopped over. I staked the plants at the bottom and supported them pretty good but the growth at the top of the plant seemed weak. Did I do something wrong or do I need to prune them a certain way? Second question, do I need to divide the dahlia clumps after I pull them out of the ground or can I just leave them all together, not divide and replant them the way they are. I'm somewhat nervous about trying to divide them.

Answer: It sounds as though your dahlias were not planted deep enough, and were not fertilized quite enough to help them develop strong, sturdy stems. All dahlias should be staked, to help the stems grow straight, and to help support the huge flower heads that the larger dahlia cultivars produce. Here's how to grow impressive dahlias: After frost kills the foliage, dig the dahlia tubers, shake off excess soil, and store the tubers in peatmoss or sawdust. The tubers should look like the spokes of a wheel with the original stem in the center. Place the entire group on a layer of peat and place more peat around them. Store your dahlias in a cool, dark location where it remains above freezing during the winter months. In the spring (about May in the Pacific Northwest) you can divide the tubers. Look for a tiny bud (or eye) on the topmost part of the tuber, closest to the stem. As you cut each tuber away from the old, dried stem, make sure each tuber has a bud. When you're ready to plant, choose a site that gets sunshine all day, and dig a hole about one-foot deep for each tuber, spaced about three feet apart. Mix 1/4 cup of complete fertilizer into the bottom of the hole, add about 4 inches of soil, and drive a 4-5 foot stake into the hole. Then plant each tuber, with the eye pointing toward the stake, and cover it with 3 inches of soil. Water well, and when the tuber sprouts, gradually fill the hole in with soil. Don't completely cover the emerging stem and leaves, but keep building up the level of soil. This method will give your mature dahlia lots of underground support. As the stem grows above soil level, tie it loosely to the stake. Dahlias growing in enriched soil won't need additional fertilizer throughout the season, but should be watered every week during the growing and blooming season. Plan to supply one-inch of water per week to each of your dahlia plants. Following the above guidelines should provide you with healthy, happy dahlias.

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