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How to Plant, Grow, and Care for Ever-Flamboyant Dahlias

Dorothy is a Master Gardener, former newspaper reporter, and the author of several books. Michael is a landscape/nature photographer in NM.

Flamboyant, Colorful Dahlias

Dahlias come in a variety of bright colors as you can see from the photographs in this article, graciously shared by the photographer, Roy Kelley of Gaithersburg, Maryland.

Dahlias come in a variety of bright colors as you can see from the photographs in this article, graciously shared by the photographer, Roy Kelley of Gaithersburg, Maryland.

Planting Dahlias: When, Where, and How

When - Early spring is the best time to start planting dahlias, but don't be in a rush if you feel like another cold snap might be coming. Patience is called for because dahlias struggle in cold soil. Wait until the ground temperature is at least 60 degrees Fahrenheit. If you want to get a jump on the growing season, you can always start your dahlias indoors, then plant them outside when the weather is warm.

Where - Dahlias need to be planted in a location that receives full sun. They need at least six to eight hours of direct sunlight, especially morning sunlight. They also need to be planted in a site that has slightly acidic, rich, well-drained soil that is protected from the wind. The pH level of the soil should be 6.5 to 7.0. If the soil is heavy, mix in some sand, peat moss or manure, which will lighten and loosen the thick soil texture providing better drainage.

If you have selected your location and prepared the soil, bedding dahlias need to be planted about 8-12 inches apart, although if you have the smaller flowering type of dahlias (usually about three feet tall), the spacing should be about 20-24 inches. Taller dahlias require even more spacing, approximately three feet between each plant.

Keep weeds away from your plantings!

How - First, avoid any dahlia tubers that look like they might be rotten. Some green growth is usually a good sign that the tuber is acceptable to plant. Never break or cut individual dahlia tubers.

Dig your planting hole about six to eight inches deep. It should be slightly larger than the root ball. Putting some compost or sphagnum peat moss into the soil, along with a small amount of bonemeal will aid in the growth of healthy plants. No other fertilizer is needed at the time of planting.

Place your tubers into the soil with the eyes facing up, then cover with one to three inches of soil. Once the stem sprouts, fill in the hole with soil until at ground level.

If you have chosen tall plants, you need to place about five or six stakes around the plant when it is planted. As your plants grow, tie the stems to the stakes using strips of soft, cotton cloth that will now cut into the plant.

Don't water your dahlias at the time you plant them. Doing so will encourage the tubers to rot. Instead, wait until sprouts have appeared above the soil.

Don't cover your dahlias with mulch or bark.

Do apply some slug or snail bait to keep those nasty pests from feasting on your plants.

Pests in Your Garden

Some of the pests you need to be on the lookout for include aphids, slugs, snails, borers, leafhoppers, and spider mites. If you find any of these, these tips will help you get rid of them.

  • Aphids - Spray them with insecticidal soap or neem oil extract.
  • Slugs - Nothing is more disgusting than the sight of a slimy trail on your beautiful leaves or even the ground surrounding your plants, so you might want to keep some slug and snail bait on hand at all times. If you see the slime, you know they are around somewhere and if so, they can destroy your beautiful garden.
  • Borers - Some signs that borers are present include stems that show breakage or wilting. Keeping weeds away from your plants should deter them, but if they've already affected your plants, cut off and destroy stems that have been larvae-infested.
  • Leafhoppers - These plant-feeding pests can destroy the look of your beautiful plant, so if you see signs of them, begin spraying (about every five days) a mix of a pint of insecticidal soap and a tablespoon of isopropyl alcohol.
  • Spider mites - Look for these pests on the underside of leaves. If you find them, wipe down the leaves with a sponge soaked in plain water or spray with Neem. You can also spray the leaves with a mixture of water and mild dishwashing soap if you prefer.

Some Dos and Don'ts

  • Don't water your dahlias at the time you plant them. Doing so will encourage the tubers to rot. Instead, wait until sprouts have appeared above the soil.
  • Don't cover your dahlias with mulch or bark.
  • Do apply some slug or snail bait to keep those nasty pests from feasting on your plants. Personally, I keep a two-pound bag of Garden Safe® slug and snail bait and have found it to be very effective. It is safe if you have pets or wildlife in the area and you can use around all of your flowers, vegetables, and trees. You can also use it inside your greenhouse if you have one.
  • Do apply a fertilizer about 30 days after planting (not sooner). Look for a fertilizer that is low in nitrogen (5-10-10 should be fine). The best fertilizer for these plants is one that is high in potassium and phosphorus but low in nitrogen, preventing leafy bushes that produce very few blooms.
  • Don't overfeed your plant. The result will be yellowed leaves and drooping, leggy plants, the overall health of which will be diminished.
  • Don't apply high-nitrogen, water-soluble fertilizers!

Propagating Dahlias

Dividing dahlia bulbs is the fastest, most direct way to propagate your dahlias. It is possible to propagate by planting seeds or by taking cuttings, but those are hit-and-miss systems that are probably not worth the trouble. Planting them from seed doesn't usually result in uniform flower forms or colors and taking cuttings is a very time-consuming, messy project.

Your next season's plants will be vital if you first separate healthy tubers from damaged or diseased ones and the tubers you painstakingly grew this year will create many more plants for your garden next year.

What to Do When the Growing Season Ends

Don't dig up your tubers to store for the winter until frost has turned the foliage black. If you are in a frost-free area, you can dig them up by the middle of November. After you have dug up your plants, remove all remaining old foliage from your garden area.

Stalk clumps need to be cut to about six inches long. Then, rinse off the soil with water and place the clump under some type of cover where it should be allowed to air dry for a full day.

If you intend to store your clumps in cardboard boxes, line the box with newspaper before layering the tubers with slightly moist sand, sawdust or peat. NEVER store in plastic. Follow the same procedure if you want to store them in terra cotta pots. Store the boxes or pots in a cool, dry, dark spot where the temperature can be kept around 40-50 degrees Fahrenheit.

Don't make the mistake of thinking your stored plants are going to be okay all winter. You need to check them about once every three to four weeks to see if they are starting to shrivel or rot. If you do see some shriveling, mist the packing material very lightly with water.

References

  1. Dahlia Disease Problems. Michigan State University Extension, January 1, 1998.
    http://www.msu.edu/msue/imp/modop/00000480.html (Retrieved from website, 4/28/2018)
  2. The Encyclopedia of Flower Gardening, Sunset Books, Menlo Park, CA
  3. The Plant World (1987) World Book, Inc. - The World Book Encyclopedia of Science
  4. Thomas, R. William (2015). The Art of Gardening, Timber Press, Portland, OR

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2018 Mike and Dorothy McKenney

Comments

Rochelle Frank from California Gold Country on April 28, 2018:

Spectacular flowers.

My neighbors in southern California used to have some.

Where I live now, it is probably too cold. And, I have to admit that they sound like a little too much work for me. Your information sounds very complete. Your friend's photos are great.