11 Tips To Keep Your Dahlias Blooming All Season Long

Dahlia addiction doesn’t happen overnight. Maybe a neighbor shared some tubers with you last spring, and you plugged a few into an open space along the fence. Maybe a gardening website hooked you with a colorful article about growing dahlias this season, and you decided to give them a try.

Once the flowers start coming, however, and you’ve experienced the thrill of these long-blooming, show-stopping garden stars – you’re going to want more. And you’re going to want to keep the thrill going for as long as possible.

Having a flourishing, colorful dahila garden can make you the envy of just about anyone visiting your garden. Consider the following steps for choosing, planting, maintaining and storing dahlia plants, and you’ll likely have beautiful blooms that keep blooming until the bitter end.

Buy Quality Stock

You’ll pay a bit more purchasing dahlias directly from a grower. But it will almost always give you the most beautiful flowers, amongst one of the most beautiful types of flowering plants. Look for established farms that specialize in dahlias and have a reputation for healthy, disease free stock. Ask around on garden forums and read through customer reviews. While you’re at it, solicit recommendations for tried and true dahlia cultivars that meet your space, height and color requirements. A little research up front will go a long way toward making your dahlia dreams come true. 

Don’t wait until the snow melts to start clicking around for delivery. You will likely be too late. Order before the holidays to guarantee spring delivery and keep your tubers cool and dry until go-time. If budget allows, purchase established dahlia roots. They will likely be more fool proof than seeds and will give you the best start.

If the dahlia bug has bitten you by surprise and spring has already sprung, don’t fret. Keep an eye out for garden club plant sales and dahlia society events. They can be good buying sources. And your local nursery will likely carry a few dahlia varieties, either in root form or as an established plant. Big box stores will also typically display a few offerings worth checking out. Your dahlias might not be as bodacious as those acquired from a grower, but the prices will be slightly more reasonable. So, this may be a gamble you’re willing to take.

Start With Good Soil

Healthy, happy dahlias require rich, well-drained soil with a slightly acidic makeup. If you are forward thinking enough, begin prepping your dahlia beds in fall by adding plenty of compost and organic matter to your soil. Grass clippings, shredded newspaper, peat moss, and dead leaves should be incorporated to invite beneficial microorganisms and aerate the dirt. Beds should be crumbly and drain quickly without puddling.

You may also want to test your soil’s pH level, if you don’t already know it. Since dahlias prefer a slightly acidic soil base, you’ll want  to work some lime into the mix if your balance is low. Conversely, a little peat moss or sulfate will help address soil with a more alkaline makeup.

Finally, top dress soil with 2-3 inches of mulch, taking care not to pile it up around dahlia stems. This will help insulate the ground and keep surface moisture from evaporating.

Plant Carefully

When it comes to planting your Dahlias, you need to plant very carefully. They love sun, but not too much of it. You’ll want to nail down your dahila planting specifics before you start, and that includes the right location, timing, planting depth and the amount of space each flower will need. Let’s take a careful look at each important factor.

Timing

Long-lasting, bountiful blooms do not erupt from mushy, frozen roots. Do not plant dahlias until all danger of frost has passed! Check your hardiness zone for the average date of your region’s last freezing temps and add a couple of weeks to be safe. Soil temperatures need to be a steady 60 degrees. For southern gardeners, it’ll be safe to plant tubers in late March or April. Northerners will have to wait patiently until at least the end of May, maybe a little longer.

Location

Dahlias require abundant sunshine to bloom blissfully. Choose a location that will get at least 6 hours a day, and take care to avoid locations under tree limbs or shadows. If you have to choose between morning sun and afternoon sun, morning is preferable. Since dahlias are often leggy and prone to snapping in high winds, a location on the south side of a fence or garage will give them optimal protection.

Depth

Paying careful attention to your dahlia’s mature height and width, dig a hole 6-8 inches deep and place your tuber at the bottom with its eyes facing up. If sprouts are already present and taller than 6 inches, fill holes loosely with dirt to ground level. If eyes have not sprouted yet, fill holes loosely with 2-3 inches of dirt until new growth has exceeded ground level, then fill in around them.

Space

Dahlias need proper airflow to discourage disease and allow for proper growth. Depending on each specific cultivar and its plant specs, you’ll need to space tubers somewhere between 1 and 3 feet apart.

Stake for Strength

All but the tiniest dwarf varieties will require staking to withstand wind, rain, and heavy blooms. At the time of planting, select a cane or stake that is equal in length to your variety’s mature height and drive it firmly into the soil about 4 inches away from the root. Visit your blooms regularly to monitor new growth (which occurs from the plant’s top) and use garden ties or cloth strips to secure their stems to the stake. Check regularly to make sure growth is not being inhibited by your ties and adjust as necessary.

Pinch for Good Form

When plants reach 1 foot in height and possess 3-4 sets of leaves, you may want to pinch or prune off their tops to encourage some side growth. Most dahlias are single-stem in nature, but performing this little garden trick early in the season will encourage more branching and greater flower production. Use a small shears or scissors to cut the tops off plants just above the third or fourth set of leaves. The process can be repeated a few weeks later to encourage even bushier dahlias, if so desired.

Water Properly

Regular, even watering is key to growing the dahlias of your dreams. Tuberous roots are prone to rot and fungus, and puddling water is their sworn enemy. During early growth, while you are waiting for blooms, keep soil moist but do not overwater. Shoot for about 1 inch of water a week, and use a soaker hose to prevent excessive moisture on foliage. Check soil with your finger to make sure it is moist but not soggy.

Once blooming has begun, dahlia roots will need a bit more water to keep nourishing their flower heads, so bump your watering routine up to about 2 inches per week for the rest of the summer. Because humidity and precipitation will vary from zone to zone, you’ll need to be mindful of rainfall and/or drought events that may throw your routine off. Most likely you will be watering somewhere between 1 and 3 times a week.

Fertilize for Flowers, Not Leaves

Depending on your soil makeup, you may want to use a nitrogen rich fertilizer while shoots are establishing, but once blooms have begun, you’ll want to dial it back. Nitrogen will give you dahlias that are bushy and leggy, but the blooms will play second fiddle to the greenery. A fertilizer with a ratio of 5-10-10 will give you more potassium and phosphorus, which will lead to more beautiful blooms. Follow manufacturer’s instructions for application, but a good rule of thumb for dahlias is fertilizing at 30 days of growth and then again at 60.

Deadhead Often

Don’t wait for fading blooms to fall off on their own. Be ruthless with the pruning shears and you’ll be rewarded with abundant flowers. Dying blooms are an indication that seed production has begun, and a flower’s growing system will then divert its focus from creating showy blooms to nurturing its roots and foliage. Removing spent or fading flowers from a healthy plant will actually trick the roots into sending up more blooms.

Make it a point to buzz through and deadhead your dahlia patch every few days to remove blooms that are on their way out. Beginning just beneath the base of your dahlia’s spent flower, slide your fingers down its stem until you reach either a set of leaves, a new bud, or a sidestem. Make your cut just above one of these points and you won’t be left with unsightly, headless stems. In just a few days, your dahlias will reward you with new growth from the nodes just below these regions, and ultimately new blooms.

Look for Signs of Distress

As dahlias are vulnerable to many pests and diseases, you’ll want to keep a close eye on them throughout the growing season. Make time regularly to examine their leaves since odd leaf color and structure are almost always early warning signs of poor health.

If you spot shredded leaves and bite marks, you may have a slug problem. Little yellow spots with black dots typically indicate the presence of sucking insects like thrips or aphids. And a sticky web will likely be the work of mites.

A chalky, gray film on your leaves is likely powdery mildew, while fungal growth at the plant base could be from root rot. Brown or black stems and leaves are an ominous sign that something viral is going on.

By carefully monitoring and swiftly addressing  ssues beneath your dahlia’s blooms, you can get out in front of pests and diseases and keep the flowers coming.

Bring Blooms Inside

Long stems and oversized, romantic blooms make dahlias a cutting garden favorite. To keep the show going inside as well as out, dahlias will need to be cut and stored with some attention to detail.

Cooler, morning temperatures will help dahlias make a smoother transition from outside to inside, so do your cutting as early as possible. Blooms will not open much more after harvesting, so choose flowers that are mostly open for your arrangements. No matter how tall your vase is, cut dahlias all the way down to their base with clean pruning shears. Not only will this look better in the garden, but it will encourage the production of another stem.

Adjust stems to desired lengths and insert their tips in very warm water. Cutting points can also be passed through an open flame to cure. Dahlias can be held in a vase full of cool water for at least a week if all goes well.

Think Ahead

When the dahlia show is over for the season and the flowers have stopped coming, it’s time to start thinking about next year’s blooms. Their roots can be dug up, overwintered and multiplied for an even more dramatic dahlia display next year.

In cooler growing zones, dig tubers up after the first frost has browned their leaves. Cut the stems off just above the eyes from which they grew, clean the roots off with a dry towel and lay them out to dry out for a couple of days. Pack your tubers loosely in a basket, box, or burlap bag and cushion with peat moss, newspaper, or sand.

Select a container that is not air-tight, as a little bit of air circulation will help prevent molding. Store in an environment with a temperature that exceeds freezing but does not climb above 50 degrees and wait for spring.