How to Plant Dahlias
Stage some floral fireworks by adding dahlias to your landscape. Learning how to plant dahlias isn't difficult. If you have zero garden experience, you can still succeed with these glamorous flowers—and really feel impressed with yourself when they burst into bloom. Follow these simple steps for planting dahlias.
Choose a spot for dahlias that’s bathed in sunlight for most of the day, unless you live in areas like Texas, the South or Southwest. In these regions where afternoon sun brings intense heat and temperatures soar above 90 degrees on a daily basis, plant dahlias where they receive afternoon shade. Dahlias that receive too little sunlight wind up with longer stems and fewer flowers. Dahlias that receive direct sunlight in scorching heat can have smaller flowers that are faded.
Dahlias pair well with roses, butterfly bush, summer lilies and fall perennials, like asters or goldenrod. Areas where these plants thrive offer good planting spots for dahlias.
While dahlias are heavy feeders, you don’t want to overfertilize soil. If your soil tends toward a fertile garden loam, don’t overdo it by adding heaps of nitrogen-rich compost to dahlia beds. Too much nitrogen can reduce flower numbers. But if your soil drains poorly (heavy clay) or has a high sand content, work aged compost or manure into dahlia planting areas. Build raised beds if your soil is rocky or shallow.
Think of dahlias like a combination of a root vegetable, like a potato, and a fruiting plant, like a tomato. You want to fertilize to encourage roots (tubers) and flowers to form. That means you should select a low-nitrogen fertilizer—something similar to vegetable fertilizers should work well. Look for numbers on the bag like 5-10-10 or 10-20-20. Work this into dahlia planting beds or individual planting holes. Fertilizers too high in nitrogen result in weak stems, small to no flowers and rot-prone tubers.
Get dahlias in the ground once soil has warmed to 60°F. This is usually anywhere from mid-April to May in most regions. It corresponds with the time you’re probably planting warm-season veggies, like peppers, squash or corn.
Plant dahlia tubers anywhere from 4 to 6 inches deep. Planting depth and spacing between tubers varies depending on the type. Follow the recommendations that come with your tubers. If you’re planting tall or dinner plate-type dahlias that need staking, insert stakes at planting time to avoid accidentally spearing tubers.
After burying tubers, do not water them in. This can lead to rot. But do apply slug and snail bait to protect new shoots from hungry critters. Dahlias take from 14 to 20 days to emerge, and snails start their shoot munching before you even spy a spot of green.
For container planting, use pots at least 12 inches wide. Bigger pots are better because they offer soil depth that supports strong top growth. You can plant dahlias in pots before ground temperatures reach 60°F, but don’t jump the gun too much. Hedge your bets by setting the soil you’ll use to fill containers in the sun a few days prior to planting.