8 Tips for Growing Better Dahlias
Dahlia fever is running wild through the gardening world and there’s no sign of it stopping anytime soon. If you have caught the dahlia bug, here are eight tips for growing bigger, better flowers this summer.
Know Your Tubers
Dahlias sprout from buds that were formed at the end of the prior growing season. These buds are located on at the base of the stem, just above where the tubers are attached.
The tubers themselves do not produce sprouts — they are food storage vessels that will help fuel the plant’s early growth. Dahlia tubers are sold in two ways: as single tubers with a bud attached, or as a clump with a stem and several tubers.
Timing is Key
If you are planting your dahlias directly into the garden, wait until the soil has warmed up to 60°F. Dahlias will not grow in cold soil and their foliage is sensitive to frost.
In northern areas, dahlia tubers can be planted indoors 4 to 6 weeks before the last frost date. Fill 1 or 2 gallon pots with moist growing mix and plant the tuber(s) with the stem or sprouts facing up. Cover with 2” of soil and put the pots in a warm place with good light. Water sparingly at first, then regularly once the plants are several inches tall. Transplant outdoors after danger of frost has passed.
Where and How to Plant
Dahlias bloom best when they’re grown in full sun and fertile, well-drained soil. Plant border dahlia tubers 15” apart from center to center; standard types are usually spaced about 18” from center to center.
Prepare the planting area by loosening the soil to a depth of 12”. Add compost and an all-purpose granular fertilizer and mix well. Dig a hole and plant the tubers, keeping the stem(s) or sprouts upright. The top of the tuber should be 3-4” below the soil surface. Backfill the hole with soil.
The Value of Pinching and Staking
When your dahlias are about 12” tall and have at least 4 pairs of leaves, pinch out/off the top of the main stem. This will stimulate lateral branching and give you a stockier plant with more stems and more flowers. For details, see HERE.
Border dahlias are self-supporting, but full size dahlias can grow as tall as 3 to 4 feet. Staking your plants or surrounding them with a metal cage will support the flower heads and help protect the stems from breaking. Read about staking options HERE.
Watering and Fertilizing
Dahlias grow best when they receive a consistent supply of water. Drip irrigation is ideal, as it directs moisture down to the root zone while keeping the foliage dry. Mulching around the base of the plants will also help to reduce moisture loss.
Dahlias are hungry plants, and they produce more flowers when they are well fed. Apply a granular all-purpose fertilizer at planting time and a liquid fertilizer once a month throughout the growing season.
Controlling Insects and Disease
To discourage disease, keep the foliage as dry as possible. Water deeply about once a week (depending on the weather and your climate) and let the top inch of soil dry out in between. Keep the area around the bottom of the plants clear. You can also clip off the bottom 12” of foliage to encourage good air circulation.
Slugs and snails are attracted to dahlia foliage and can munch down a young plant overnight . Sluggo pellets are an effective organic control when applied early and refreshed often. Earwigs are another annoying dahlia pest. They eat dahlia buds, flowers and foliage. When you’re deadheading or trimming back your plants, clean up the area and remove any spent flowers or foliage. This will give earwigs fewer places to hide and breed.
Be Generous
Dahlias are among the world’s best cut flowers and it takes just a few stems to make an impressive bouquet. Harvesting flowers is good for the plants and encourages them to continue flowering month after month. Spread the joy and delight your family and friends, neighbors and coworkers with the beauty of your homegrown dahlias.
Deadheading
Removing flowers that have passed their prime will keep your plants looking neat, encourage them to produce new buds and help control pests and disease. If you’re in a hurry, simply nip off the flower heads. Otherwise, use scissors or pruning shears and cut back to a main stem. This will stimulate new growth and longer stems that are better for cutting.
Ready to learn more about growing dahlias? You might be interested in reading All About Dahlias, How to Grow Border Dahlias and Types of Dahlias. To shop our full line of dahlias, which may be pre-ordered January-March for shipping April and May, click HERE.
Great information! I’m ready to plant!
Hi Carol – Thanks for your comment. Hope your dahlias bloom beautifully for you this summer.
I bought a couple of dahlias with dark foliage this year, that were labeled as annuals. Are there different types? I live in zone 6.
Hi Margaret – There are quite a few dahlia varieties with dark foliage. They have the same hardiness rating as other types. Dahlias usually will not survive winter temperatures in zone 6. You can either treat them as annuals or dig the tubers in late fall and store them indoors for the winter.
I have lots of buds but when they start to open they now are very faded. They are suppose to be bright orange but instead they are a yellowish brown.
Hi Amy – It sounds like your dahlias are showing signs of stress. This can be caused by many different things: too much or too little heat, sun, moisture, or fertilizer. If you have had good luck growing dahlias in the past, this may just be a temporary condition and hopefully the plants will return to normal. Cut off those stems and give your dahlias some extra TLC. If you live in a hot climate, you may be interested in the tips in this article: Growing Dahlias in Hot Weather.
In my part of the U.K. it’s warm enough to leave my tubers in over winter. I pile leaves on top to act as extra insulation and a ‘roof’ for the tubers so they are slightly drier than the surroundings no soil.
In spring how shall I incorporate a fertiliser feed?
Hi Anne – That sounds like an excellent way to protect your tubers during the winter. In spring, I would top-dress them with a combination of compost and a low-nitrogen, granular organic fertilizer. Foliar feeding is a good way to provide a boost of nutrition during the growing season.
Will my dahlias grow and bloom well in a 3 gallon pot? I am in zone 7b.
Hi Miriam – Any border dahlia will do fine in a 3 gallon pot. A 5-gallon pot is best for a full-size dahlia. That said, you can probably be successful with a decorative dahlia (not a dinnerplate-size) as long as you are able to water daily and fertilize regularly. For best results, look for a variety that is shorter than average – 3-feet tall or less.
The pkg says to plant 5” deep, but above you say 2”…..?
Thanks!
Hi Linda Sue – When planting, the crown of the plant (where stem meets tubers) should only be 2″ deep. You can hill up a few inches of soil around the base of the plant after it is well-established. Some people find this is helpful. But when getting started, it’s best for those young dahlia sprouts to emerge easily/quickly.
Help! My tubers have been in pots inside for about three weeks. The eyes have sprouted to skinny, up to 12 inches tall plants. I live in zone 5b and am getting ready to plant them in big containers. When I plant should I follow the directions to plant the stem (the round one that came with) 2” deep and have part of the sprouts under the soil?
This is my first attempt at dahlias and I’d like to have A successful experience. If They “go” I’d like to continue growing dahlias for years to come.
I’ll look for your helpful advice.
Thanks,
Susan Snyder
Hi Susan – Please do not bury the stems. The top of the dahlia bulb clump should be no more than 1-2″ below the soil surface. You can pinch back the leggy stems to encourage stockier growth. Having 2-4 stems per plant is about right. See our article HERE on how to pinch dahlias.
I live in Northern New Jersey and planted some lfgardens Kordessa and Zirconia dahlias this spring. After coming up and looking very healthy for several weeks and inches tall, a couple of the plants have just wilted and gone limp. One of them, planted in a large pot and miles away and in different soil than the other one with this problem, is still green. But all limp. What’s going on?
Hi David – two things come to mind as possibilities: overwatering or rodents. Young dahlias are very sensitive to overwatering. Better to let them get a bit dry than to spoil them with too much water. If you see any digging, it could be voles going after the tubers.
I also find that sometimes dahlia plants hit a rough spot. For one reason or another some of the leaves will curl or brown or die back. Sometimes an entire stem will die back. A good thing about growing dahlias from clumps (like you receive from Longfield Gardens) vs. individual tubers (from most US growers) is that the clumps will usually send up a replacement shoot. So be extra careful to ensure you are not overwatering, and hang on. It’s likely your plants will revive.
One other option is to very gently dig up the tuber to see if you can tell what’s happening underground. There is a risk of damaging the plant, but if you can do it carefully, you will probably learn a lot. If you find that parts of the tuber are soft, it has been overwatered and is rotting. Hopefully there are other sprouts forming and you can simply replant and wait. Longfield Gardens does guarantee that our plants will grow as long, so please contact our customer service department if these plants don’t pull through.
I have a huge kettle where I always plant a variety of flowers. I love dahlias and have planted them before. This year I planted a small dahlia plant and it quickly grew about three flowers. I dead headed the blooms when they turned brown by just pulling them off. I read tonight that you are supposed to deadhead by cutting the stem near the leaves. So I am wondering now if that is the problem since I have three more flowers but they are buried beneath the foliage. Should I cut back the foliage?
Hi Wendy – Dahlias come in different sizes. Did you plant a full size variety that will grow 3 or 5 feet tall, or a border dahlia that will mature at 18 to 24″ tall? If you have border dahlias, it’s normal for the flowers to have stems that are just a couple inches long. When you cut off the spent flowers, just cut their stems, too. No one has snips in their pocket at all times, so all of us just pull off flower heads now and then. It doesn’t hurt the plant. Full size dahlias can take a few weeks to find their groove with respect to flowering. Until then, they will often produce flowers with short stems. Don’t remove any foliage. Just cut the flower back to a main stem and the plant should eventually start producing longer stems.
I bought some Dinnerplate Dahlias (Kelvin Floodlight & Babylon Red) in time to get them into the ground, but we had heavy rains, hail and winds which means the weeds grew like crazy. i just finished weeding the garden and flowerbeds and its the end of August!! My common sense tells me not to plant them now (too late?). My question is; can I store them another year in the garage for the winter?? what to store them in (original plastic, wood shavings, or?? I have never grown dahlias before and I am totally new to flower gardens anyway, so I am really anxious to see if I can be successful with them. Thank you for your help.
Hi Karen – Yes, it’s too late to plant them now. Unfortunately, those tubers will not be alive next spring after being out of the ground for 18 months. Doesn’t matter how you store them. We want you to succeed as well and recommend planting fresh tubers next spring. Now your garden will be all weeded and ready to go next spring!
I had boatloads of flowers but very weak stems. What could I do to make the stems more substantial so they would hold the heads up when cut?
Hi Carol, the thickness and strength of the stems varies a lot from one dahlia variety to the next. So you may want to try growing some different varieties. Potassium helps to strengthen plants, but your soil may already have enough potassium. Consider having your soil tested to see if there are any nutrient or micro-nutrient deficiencies. Another option is to enrich the planting area with high quality compost. It’s the easiest way to provide plants with a balanced source of nutrients without any danger of creating soil imbalances.
Can I separate the tuber? Or do I plant the wjole bunch in one hole? Thanks for your help’
Hi Estrella – you can do either of these. If you divide the tubers, make sure each division has at least one “eye” (latent sprout). There’s an article about this on our website : longfield-gardens.com/article/Dahlia-Tubers-What-You—Need-To-Know
I love in zone 7b, planing to build a retaining walls in my garden in May. I already have many Dahlia’s planted in past couple of years. Can I dig them out (carefully) and store them about a month and then replant them again?
Hi Nelly – yes, they should be fine as long as you dig them early. The way the stems attach to the tuber is not very secure so it’s difficult to move a plant without breaking them off. As you note, the tubers are brittle, so just go slowly. Good luck!
Crystal- 3/11/21- I live in zone4 and have purchased dahlias from you in the past. I put the tubers in a large pot in the fall and “buried “them in soil. Put the large pot in the garage and just took a peek at the tubers, and there is no growth! How should I handle the situation? I just purchased 2 more bags from Longfield Gardens sold at Costco, and just opened the bags…no growth. Should I plant the tubers in small pots now and begin watering a little? Not sure how to create growth in March.
Hi – I am also in zone 4 and all my overwintered dahlias are still dormant. It’s too early for them to show any signs of sprouting. That may not happen until mid-April. The same goes for newly-purchased tubers. It takes some time for them to wake up. You can start potting them up now in pots with barely moist soil. Once the sprouts appear above the soil surface, they will need light. But until then you can keep the pots just about anywhere that’s relatively warm. As long as the tubers in your garage did not freeze or completely dry out, they should be fine. Good luck!
My friend gifted me a ” 14 GRAPE GARDEN MIX DECORATIVE DAHLIAS” from Costco. There are 3 bags, 2 are labeled “A”, and 1 “B”. From the picture, it appears there are 3 varieties, 1ea pink, white and purple.
What is in the “B” bag?
More importantly, MOST of the tubers have broken necks and dangle off the main shoot they are attached to. Isn’t it true that those with broken necks will not grow?
Hi Nancy – don’t be concerned about the letters on the bags. We offer many different dahlia mixes, and use this lettering system to get the right color balance for each mix.
Regarding the broken necks on the dahlia clumps. This happens when the clumps are washed in Holland. Some years we see more damage than others. This short video on our YouTube channel shows how you can clip off the dangling tubers. With dahlias, the eyes (which will become the sprouts) form on stem tissue, not on the tubers. So as long as there are viable eyes, the clump should grow just fine. This article shows the eyes clearly and explains a little more about what to expect: Dahlia Tubers – What You Need to Know.
Hi Kath,
I live in northeast coastal zone 5b and last year I started my dahlia tubers indoors in pots around mid April, then transplanted them into the garden in June. That worked fine. But this year my dahlia addiction has grown along with my enthusiasm for flowers and I won’t have enough room in my house to start both my overwintered dahlias AND the new dahlias I have ordered from Longfield in pots. If I do, I might have to move out because the plants will certainly take over. I’m looking into getting cold frames or a greenhouse of some sort to put the dahlias in once I start them in pots but could use some guidance about what could work best for my zone. Which type of cold frame or greenhouse would you recommend for a small back yard? Also, would it be too cold for the dahlias to start them in pots outdoors in a cold frame or green house in mid April? Any advice would be much appreciated. Thanks!
Hi Molly – I am in zone 4B and usually start about 80 tubers in 1 gal and 2 gal pots. You are right — that many pots occupies a lot of space. After planting, I find it usually takes several weeks (up to a month!) for the tubers to sprout. While waiting they need warmth but not light. This gives you some options. Consider a technique used by Erin at The Impatient Gardener. She plants her tubers and then stacks the pots on top of each other until they begin to sprout. After I plant the pots, I leave them in the basement for a couple weeks while they are starting to wake up. It’s not as warm as they would like, but gives me the extra 2 weeks that I need before it’s warm enough for them to go into the greenhouse.
My greenhouse is unheated. I move the pots out there in mid-April when it can still get very cold here (you’ll be safer in 5B). So I cover the pots with two layers of garden fabric to hold in daytime heat and protect them on cold nights. They do just fine. Within a few weeks (first half of May) the days are getting warmer and the plants start to really take off. I can usually plant them out into the garden at the very end of the month.
Erin uses two small, tent-like plastic greenhouses for her dahlias. A cold frame would work fine as well, although the pots will fill it up very quickly. Another option would be to create a temporary plastic/garden fabric tunnel using wire hoops. Cover it April 1st to warm the soil, then move your pots out there under cover. Beware of unvented plastic, which heats up quickly on sunny days and could cook the plants. I’d use one or two layers of thick garden fabric such as the “GardenQuilt” offered by gardeners.com. I have been using it for 30 years — especially in my vegetable garden — and can’t imagine gardening without it. Hope this helps!
Thank you, Kath! I appreciate you taking the time to write me back and share all of this very helpful advice. I think I’ll give either the cold frame or a tent-like greenhouse a try for this spring and see how it goes. I’ll plan to pot up the tubers in mid April, stack them and let them wake up for 2 or more weeks in my basement (which is usually around 65-70 degrees), and then move them out to the cold frames or tent greenhouse in early/mid May (if that sounds good to you). Would you still recommend covering the pots with garden fabric at that point? Also, how would you harden the dahlias off in the cold frames or tent greenhouse before planting them outside (I’ll aim for June 1st since that’s when I usually plant my tomato seedlings outside too). So much to learn 🙂
I have learned that dahlias dislike temperature extremes. It can really disrupt their performance. So do whatever’s necessary to coddle them during the spring — until the day/night temperature differential has settled down. As I mentioned, garden fabric is very helpful for this. It also shields the plants from wind. Harden off your dahlias just as you do tomatoes: protect from wind, gradually increase direct sun exposure. Good luck!
Hi Kath, I’m gearing up to start my dahlia tubers early in 1-2 gallon pots in the next few weeks (some of them overwintered in storage well and are just starting to sprout eyes!) and wonder what kind of growing mix you use (there are so many kinds that it’s a bit overwhelming) and if you give the dahlias any kind of specific fertilizer once they begin to sprout in their pots? I will also try growing some of the dahlias in big terra cotta pots out in the garden this summer and wonder if you recommend using a general organic potting soil at that point and perhaps a different kind of organic liquid fertilizer for those dahlias? Thank you!
Use any high-quality soil-less growing mix for starting the tubers. I buy mine in 2 or 3 cubic foot bales at my local feed store or sometimes at Home Depot. Brand names vary by location. If you are growing dahlias in containers for the summer, I recommend adding compost to this mix. It will help with water retention as well as provide nutrition. My container mix is usually about 25% compost.
Water sparingly until the plants are in active growth. Before transplanting into the garden, I incorporate an all-purpose organic granular fertilizer in the planting area. Don’t start using a liquid fertilizer until the plants are at least a foot tall. Fertilizer recommendations vary greatly. I feed my dahlias with a product called Morbloom and alternate that with a liquid seaweed.
Thanks so much, Kath. So helpful. My local hardware store has 3 cubic foot bales of PRO-MIX BX, which is a combination of vermiculite, perlite and peat moss. Would something like that work okay for potting up the dahlias early and then amending it with compost later for the ones that will go into the garden in terra cotta pots?
Yes it will!
I’ve had trouble with my dahlias changing colors. I usually dig my tubers at the end of the season , mark them and then store them. When I replant them for the new season I end up with all one color. One year I ended up with a white with purple. Another year they all seemed to turn a peachy orange. Am I going crazy?
Hi Judy – You’re not going crazy. I wrote an article about this topic — it’s on our website:
Can Dahlias Change Color?