Dahlias: How to buy, stake and over-winter

Whether you're new to growing dahlias or a seasoned veteran, these tips will help you become a dahlia-lama!

These tips will help you get started with growing dahlias, staking dahlias and preparing your plants for winter.

getting started

There are several ways to grow dahlias.

  • give tubers a try. The most common way to grow dahlias is to buy tubers—sweet potato-like bulbs sold singly or in clumps. Plant tubers 4 to 6 inches deep in your garden in mid- to late spring (about the time you get your summer vegetable garden started). Their shoots emerge in 2 to 3 weeks and usually start blooming in mid- to late summer. Or, get a jumpstart by planting the tubers in pots in early to mid-spring and keeping them in a warm, bright place indoors. Transplant them in your garden once all danger of frost has passed.
  • buy plants. You may be able to find already-growing dahlias in cell-packs or pots at your favorite garden center. Compact types—also known as bedding plants—are ideal for edging or for filling small flower beds, pots or planters. Garden center dahlias are often already blooming, so you can be sure the color and form will be exactly what you want.
  • start from seed. If you've grown annuals or vegetables from indoor-sown seeds before, you can use the same techniques to start dahlias in late winter to early spring. Plant seedlings in outdoor beds after your last frost date for months of beautiful blooms. This is a wonderful way to get lots of plants quickly and inexpensively. Seed-grown dahlias usually produce a range of flower colors. Some types, such as ‘Bishop's Children', may also produce plants with bronzy to purple foliage.

easy options for staking tall plants

If you've been avoiding growing dahlias because of their reputation for needing time-consuming staking, you're really missing out. Here's how to make staking easier—or even eliminate it altogether.

  • single stakes. Support is important for the tallest types of dahlias—especially those with large, double flowers. One option is a sturdy wooden or metal stake. Place it in the hole at planting time, before you set in the tuber or plant; then replace the soil. As the stems grow, secure them to the stake with yarn, strips of fabric or Velcro tape every foot or so. This sort of staking is easiest in a vegetable or cutting garden, where the plants are growing in rows and you can easily reach them for tying.
  • tomato cages. Sturdy metal cages are as good for supporting dahlias as they are for tomatoes, and you can add them any time before the plants start to get bushy. Paint them black to make them less visible if you want to use them in ornamental beds and borders.
  • "Make staking easier."

  • decorative supports. Known variously as tripods, obelisks and tuteurs, these vertical, wooden or metal supports are charming additions to flower beds and borders. Install them right after planting—they'll add interest to your garden right away—or wait until your dahlias are growing. Stems come up through the center and lean on the sides and cross-braces for support.
  • quick fixes. Garden suppliers sell a variety of support systems that you can use to provide temporary support for dahlias that are starting to sprawl. Try linking stakes or half-circle supports to prop up whole plants or Y-stakes to hold up individual flowering stems.
  • no-stake strategies. Dahlias that don't grow more than about 3 feet tall—particularly those with small or single flowers—generally don't need support, especially if you pinch out the shoot tip when the main stem is 12 to 18 inches tall to get a lower, bushier plant. Also look for hybrids that have been selected for strong stems, such as the Karma Series. In beds and borders, combine dahlias with bushy, supportive companions, such as asters, goldenrod, ornamental grasses and compact shrubs.

what about winter?

Deciding what to do with your dahlias at the end of the growing season can be as simple or as complicated as you want to make it.

  • treat them like annuals. These days, most dahlia tubers cost no more than other fancy potted annuals—and they deliver no less drama—so, there's no need to feel guilty about pulling them out once they're nipped by frost, adding them to your compost pile, and starting with new ones each spring.
  • leave them in the ground. Dahlias can survive the winter outdoors where the soil doesn't freeze more than an inch or two deep (roughly Zone 8 and south), as long as the soil is exceptionally well drained. You run the risk of losing them in an unusually cold winter, but that may be worth the ease of growing them like other perennials most years.
  • dig them up. If you want to try keeping your favorites from year to year in colder areas, cut the frost-killed tops to about 6 inches, dig up the tubers and label each clump. Store them at 40°F to 50°F in boxes or plastic crates with a clump of soil around the roots (add a bit of water once or twice during the winter to keep the soil from going bone-dry), or gently brush off the soil and store the tubers in barely moist vermiculite, sawdust or sand.