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With a rainbow of colors and fabulous combinations, petals that are long and spiky (cactus), short and rounded (waterlily), or twisted and curled (novelty), 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 small “eyes” that sprout to create new plants. Our dahlias are sold as pre-trimmed clumps with multiple eyes around the collar. Dahlia clumps are funny looking; don't let that fool you. They'll grow into beautiful flower plants.
Dahlias need good sunlight to develop into strong plants and thrive. Find a spot that is sunny all day or most of the day. Sites with minimal wind are best. In very hot regions, afternoon shaded is beneficial, to provide protection from scorching late day sun.
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 large pots and other 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.
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 in the garden 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.
Examine your root clumps and trim off any dried up tubers or ones that are dangling loosely. These won't support the plant's development and aren't needed. 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. Often the eyes are are not visible; don't worry if you can't see them. Learn more about dahlia eyes here: Dahlia Eyes
Place the clump so the eye or the collar area is about 4-5” below the soil level. Cover the tuber clump with soil and pat lightly to settle soil. When planted outdoors, it's not necessary to water unless the soil is exceptionally dry. 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. Make sure to choose a container with drainage holes in the bottom so water doesn't collect there and encourage rot.
Sprouting typically take 2-4 weeks, but can take up to 5-6 weeks, depending on variety, temperature and individual dahlia. In general, the cooler the soil, the longer it takes for sprouting to occur.
In all but the driest of situations, resist the urge to provide more water as tubers in continuously moist soil can rot. If your dahlias haven't sprouted in 3 weeks, give them a bit more water as a gentle nudge. Then refrain from giving more.
Most full size varieties benefit from staking and virtually all big dinner plate dahlias require support. Staking your dahlia garden as you plant reduces the likelihood that you'll skewer the tuberous roots later on.
In the garden, space your plants so they have enough room to grow without crowding. Allow a space that’s 18-24” for full size dahlias and 16-20” for compact dahlias. Keep an eye out for notes in the cultivar description that mentioned "very large" and give these plants a bit more room.
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 an increasing amount of water as they get larger, so don’t be stingy at this stage, 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 dahlia flower buds are 3/4 open cut the flowers and gather them into bouquets to enjoy and share! Dahlia plants produce more flowers when trimmed regularly so feel free. Mid to late summer through first frost is a glorious time in dahlia borders and cut flower beds!
Dahlias grow well in average soil and don't need lots of fertilizer. In fact, excess fertilizer, particularly those high in nitrogen can promote weak stems, lots of foliage at the expense of flowers and tubers that fail to store over the winter. A light application of 5-10-10, 10-20-20 or similar ratio fertilizer once a month, starting 30 days after planting, is sufficient. More is not better. Avoid potting mixes with fertilizer already incorporated as it may burn the tubers. Dahlias grown in containers benefit from fertilizing every two weeks with a low nitrogen mix.
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. The tender tubers should overwinter in the ground just fine.
In colder regions, if you plan to dig your tubers, let the plants go through several light freezes before digging. This helps harden the tubers which increases their chance of staying firm while being stored 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 delicate balance between too much and too little moisture during storage.
See how to dig, trim and store your dahlia tubers for next year in this video: Storing Dahlia Tubers for the Winter
Remember to label the tubers as to variety; it's easy to forget. Come spring, replant for another year of glorious blooms!
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
They Start Out Looking Like This:
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