SUMMER-LONG BLOOMS
Dahlia Tubers Growing Guide
Dahlias are prolific bloomers that put on a spectacular show from July right through to frost, offering an incredible variety of colors, sizes, and forms to suit any garden style.
They make exquisite cut flowers, bringing that garden-fresh beauty indoors throughout the season. With basic care, they're surprisingly easy to grow, and you have the flexibility to treat them as annuals or lift and store the tubers for replanting year after year.
Please scroll down for our dahlia growing guide.
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How To Grow Dahlia Tubers
Growing dahlias in Alberta is rewarding and easier than you might think. These showstopping blooms thrive in our prairie summers, delivering abundant flowers from July through fall frost. Whether you're new to dahlias or expanding your collection, this guide covers everything you need to know for growing success.
Site Selection
Sunlight: Choose a location with full sun (at least 6 hours daily). More sun equals more blooms.
Soil: Well-draining soil is essential. Dahlias don't like wet feet. Amend heavy clay with compost, sand, or organic matter. Rich, humus soil produces the best results.
Spacing: Plant dahlias 18-24" apart to allow for air circulation and growth.
Protection: Consider a location with some protection from strong winds, especially for tall varieties.
Planting Your Dahlia Tubers
Waking a tuber from storage
- The tubers that we mail out in the spring have already been warmed up for a few weeks. They have been taken out of cold storage to begin 'eyeing up' and are ready for planting in small pots.
- If you are waking up your own tubers, take them out of cold storage for 3-4 weeks before potting up (or planting outside). Simply move them to a warmer space while retaining humidity in their storage container.
Starting Indoors (Recommended):
- Plant tubers in small pots 4-6 weeks before outdoor planting
- Use porous potting soil mixed with compost. Lightly pre-moisten soil so it is not powdery dry, but not too wet, you should not be able to squeeze water out (too wet).
- Tubers can rot easily when they are not in a growing stage yet, so be cautious not to over water. However, if soil and air is too dry, tubers can also dry up (desiccate) if they are slow to sprout.
- Cover tubers lightly with soil so the "eyes" (growth tips) don't stick out and dry out. You can also put a little plastic bag tent over the top of the pot to keep some humidity in without having to water.
- Do not put your tuber under grow lights until there are some green shoots. It is too easy to "burn" the top of tuber (eyes) if grow lights are hot and cause the soil and tuber to dry out too much. Just keeping it in a normally lit room is fine.
- Mist soil surface every few days/once a week until you see sprouts.
- Once you can see green shoots coming out to the soil, you can start watering lightly once a week.
- Once you have a some shoots you can place your plant in good light/under grow lights and keep slightly moist but not wet
When to Plant Outside:
- Transplant outside once frost danger has passed (same timing as tomatoes)
- Soil temperature should be warming
- In Alberta, typically late May
Planting Outside:
- Dig a hole 6"- 8" deep
- Add compost or bone meal to the planting hole
- Place your plant in the hole so the top of the tuber is 3+" below the surface of the soil. Remove any lower leaves that may get buried. This dirt will help provide some physical support for the stems as they grow.
- Tubers can be planted directly in the soil without pre-sprouting a plant, but there is a higher chance for tuber rot in the cool wet spring when not sprouted.
Important: Handle tubers carefully as the "eyes" (growth points) are fragile and won't grow if damaged.
Staking
Most dahlia varieties need support as they grow.
When to Stake:
Install stakes at planting time or use tomato cages to avoid damaging roots later.
How to Stake:
Use sturdy stakes or supports and tie plants with soft twine as they grow. For multiple plants, consider using t-posts with horizontal support lines.
I don't always stake my plants, but I find planting many plants close together helps keep them up as they lean on each other.
Watering
Young Plants:
Don't over water to prevent rot. Water sparingly until established.
Established Plants:
- Once plants are growing well in your garden they enjoy more frequent watering.
- Water deeply when rainfall is less than 1" per week
- During hot, dry periods, water every 2-4 days if possible
- Plants need consistent moisture for best bloom production
Feeding
At Planting:
- Mix compost or bone meal & blood meal into soil.
If you have a Newer Garden Bed
Plants receive nutrients from the soil through a symbiotic relationship with fungi/bacteria life in the soil. (Similar to how your gut flora helps you derive nutrients from your food)
New garden beds often lack soil life. To add life to your soil to help your plants be efficient at nutrient uptake you can do the following:
- add worm castings to soil
- mulch (keeps soil life cool and moist)
- add a product called Mykes to the roots during planting (mycorrhizal powder)
- If you live near a natural treed area,
collect the spongy decomposing leaves/bark/sticks from the forest floor. You may even see desirable white stringy bits of fungus growing within this. Collect, keep it moist and shaded, and then add it in your garden or mulch your plants
with this.
During Growing Season:
- I personally focus on using natural amendments/compost at the time of planting and let plants and soil life take care of the rest.
- During the growth season I may use some seaweed fertilizers for young plants when soil life is still waking up in the cool spring. I may also add a calcium amendments to provide strength to fast growing plants. (Personally I used eggshells mixed with some vinegar and left for a few days and then dilute and water with it)
- Traditionally it is recommended to use a balanced fertilizer every 2-3 weeks or one lower in nitrogen, as too much nitrogen produces leaves but fewer flowers
Ongoing Care
Deadheading: Remove spent blooms regularly to encourage more flowers. Cutting off old blooms will also help your plant produce healthier tubers later on.
Pinching: For bushier plants with more blooms, pinch the main stem when plants are 12-18" tall (optional). I usually only pinch off a few of my early plants as our growing season is short.
Pest Management: Watch for aphids, thrips and slugs. Handpick or use organic controls as needed. I recommend watering plants with molasses in dry hot times, it helps increase the sugar content of plants (their Brix number increases) which makes them less tasty for bugs like thrips. Unsulphured, organic is my preference, or bulk from farm stores as it is used in cow feed.
Disease Prevention: Ensure good air circulation, keep plants well watered and remove lower dead leaves to prevent powdery mildew.
After Blooming
Option 1 - Treat as Annual:
Allow frost to kill plants and compost the tubers.
Option 2 - Store for Next Year:
- Cut back on watering your plants by mid September. This encourages tubers to cure for better storage.
- After first frost blackens foliage, cut stems to 6"
- If you want to let your tubers 'eye up' leave the frosted plants in the ground for up to 10 more days. Alternatively, you can dig them up immediately, the tubers will naturally eye up next spring as well.
- Carefully dig tubers with a garden fork
- Brush off excess soil (no need to wash as some soil helps keep the moisture in and keep tubers plump)
- Dry tubers for a few days in a protected area. Be sure to tip tubers upside down so water can drain out of stalks to prevent rot. The stalk is usually the riskiest area to develop rot and ruin tubers in storage
- Store in boxes with peat moss, vermiculite, or sawdust
- Keep in a cool, dark location around 5 degrees celcius (40-50°F),
- Check periodically and mist lightly if shriveling
Troubleshooting
No blooms?
May need more sun, less nitrogen fertilizer, or time to establish.
Yellowing leaves?
Could indicate overwatering, poor drainage, pests or disease. My first check is for spider mites or aphids on the underside of leaves that I wash off. There are also helpful beneficial bugs you can order online from "The Bug Lady" that can help prevent or deal with "bad bug" infestations.
Stunted growth?
Check for pests, improve soil drainage, or add nutrients. Cut back other plants that may be shading out a stunted dahlia.
Tubers rotting?
Too much water or poor drainage. Ensure soil dries between watering.
