Dahlia Planting Guide

With a rainbow of colors and fabulous combinations, petals that are long and spiky, short and rounded, or twisted and curled, and flowers sizes to match any desire, dahlias are tremendously popular. Deservedly so. Beautiful for gardens and cutting, dahlias bring big personalities to any space. If you haven’t grown dahlias yet, make this your season.

Dahlia tubers are a bit like potatoes with “eyes” that sprout to create new plants. Tubers are sold as either individually with a single eye, or as full clumps with multiple eyes. Both will grow into remarkably large, strong plants in just a few months.

Planting Information

Choosing a Site

Dahlias need good sunlight to develop into strong plants. Find a spot that receives all day or ¾ day sun. Sites with minimal wind are best. In the hottest regions, some protection from scorching late day sun is beneficial.

Soil Prep

Because dahlias are vigorous and produce so much growth – both stems and flowers, and clumps of underground tubers – in a single season, they need fertile, well-drained soil. When planting in garden beds, consider adding some compost to supply nutrients and improve drainage. In containers, start with any balanced commercial potting soil. Adding a slow release fertilizer to feed your plants all season is an easy way to ensure sufficient nutrients for a great display. Pelleted Osmocote is a good fertilizer.

When to Plant

Plant outdoors when all danger of frost has past, night temperatures are in the mid to high 50s and the soil is warm, about 60 degrees. A good rule of thumb is to plant dahlias about the same time tomatoes go in the ground. Dahlia tubers planted too early in cold, moist soil are prone to rot. If your tubers arrive before the soil is warm enough in your area, feel free to get a jump on the season and start them indoors.

When potting dahlias to start indoors or to grow in containers, consider temperatures. Dahlias sprout in response to warmth and a small amount of moisture. Pots placed outdoors when night temperatures are in the 50s and 60s will take considerably longer to sprout than pots started inside at 70-80 degrees. 

How to Plant Dahlia Tubers

Examine your clumps and trim off any dried up tubers or ones that are dangling loosely. These won't support the plant's development. Find the cut-off stem from the prior year and plant this facing up. The eyes, or sprouting points, are located around the collar, where the stem attaches to the tubers. Look for little bumps – these are the eyes. Sometime the eyes are are hard to find and they are more obvious in some varieties than others. Don't worry if you can't see them. Place the clump so those eyes (or the collar area) is about 4-5” below the soil level.

Cover the tuber clump with soil but don’t water. The existing soil moisture in most outdoor sites is enough to nudge the dahlias to wake up. If planting in dry potting soil, water once to moisten soil and then wait for sprouts to emerge. This typically take 2-3 weeks, but can take up to 5, or even 6, weeks. If planting in a container, be sure to choose a pot with drainage holes in the bottom. In all but the driest of situations, resist the urge to provide more water as tubers in overly moist soil can rot. If your dahlias haven't sprouted in 3 weeks, give them a bit more water. Nudge, nudge.

Dahlia Spacing

In the garden, space your plants so they have enough room to grow without crowding. Allow a spot that’s 18-24” for full size dahlias and 16-20” for compact dahlias.

During the Growing Season

Begin to water your dahlias when your see the first sprout. Water when the soil is almost dry but never to the point where it’s continually soggy. Dahlias develop into substantial plants and consume a fair amount of water, so don’t be stingy, but know that tubers may rot in consistently wet soil. 

To encourage branching and greater flower production, pinch dahlias when they have three sets of leaves. (This isn't necessary for compact varieties.) Cutting or pinching out the main shoot above the third set of leaves prompts the plant to put energy into developing side shoots that become branches and create a fuller plant.

When the flowers show up, get out your scissors and cut! Dahlia plants produce more flowers when trimmed regularly so feel free.

Saving Tubers at Season’s End

At the end of the season you can choose to leave your dahlias in the ground or lift and store for next year. If you garden in zones 8-10, there’s no need to dig your tubers up. They should overwinter in the ground just fine.

In colder regions, if you plan to dig your tubers, let the plants go through a light freeze or two before digging. This helps harden the tubers which increases their chance of staying firm while being held for next spring. Cut the stems to within 3" of the ground, dig, brush/wash off the soil and let the tuber air dry for a day or two. Store the tubers in cardboard boxes lined with newspaper and filled with very slightly damp peat moss or vermiculite. Site the box in a cool, dark place; temperatures of 40-55 degrees are ideal. Check the tubers every couple of weeks. Sprinkle with a little water if they seem to be drying and shriveling. Trim off any mold/rot that may appear and allow for better ventilation if the tubers start to soften. There's a balance between too much and too little moisture during storage.

Remember to label the tubers as to variety; it's easy to forget. Come spring, replant for another year of glorious blooms!

Insider Tips

  1. To grow the biggest dinnerplate dahlias, pinch out the plant's center shoot just above the third sets of leaves when your dahlia is 15-20" tall.
  2. Dahlia buds aren’t always easily distinguished from spent flowers. Use your fingers to squeeze gently. Buds are hard because they’re full of petals-to-be. Flowers gone by are soft and squishy; snip them off at the bottom of the stem.
  3. Pollinators love dahlias, especially the varieties with exposed centers. And because dahlias are still flowering in September and sometimes even October, they provide a welcome late season pollen source for honeybees.
  4. Slugs also love dahlias. Control them with your favorite slug bait, especially when your plants are small and most vulnerable.
  5. Dahlia tubers vary wilding in both size and shape. Some are huge, some petite. Some tubers are long like a sweet potato and some are ping pong ball round. The variations are due to genetics, not quality. Think of the ways kids look different and are all over the board size wize. Dahlias are similar.
  6. Receive your dahilas before you're ready to plant? Keep them in a cool, dark area until you're ready.
  7. Are your dahlias itching to go and sprouting before you're ready to plant? This is normal and not grounds for concern. Trim the sprouts to 1 1/2" and plant as usual.
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Success Snapshot

Light: Full to 3/4 day sun

Soil: Fertile and well drained

Depth: Plant clump stem or rhizome 4” down

Water: Average moisture

Uses: Beds, pots & window boxes

Tip: Start indoors for longest season of bloom

GUIDE: Dahlia Planting Guide

They Start Out looking Like This: