How To Grow Dahlias
Want to learn how to grow dahlias? Here is an overview of the basics, and my collection of dahlia growing resources!
The Basics: How to Grow Dahlias
WHEN AND WHERE TO PLANT:
Plant in a spot with at least 8 or more hours of direct sunlight. In very hot climates, plant where they receive morning sun and afternoon shade. They should be planted after your regional “last frost” date (usually in mid-April or May), when the soil temperature is at or above 60 °F/ 16 °C. A few inches of quality compost and an application of fertilizer are recommended at planting time, though soil testing and regionally specific fertilizing advice should be sought. Don’t over fertilize: if dahlias are given excess nitrogen, they grow larger plants with fewer blooms. They prefer a soil pH of 6.5-7.0. Remember, dahlias are highly susceptible to rotting if soil drainage is poor. They don’t compete well with weeds or grass.
HOW TO PLANT:
Space plants 18 inches (46 cm) apart. To plant a tuber, dig a hole slightly wider than the tuber and about 4-6 inches (10-15 cm) deep. The tuber should lay horizontally in the hole, with any visible eyes pointing up. Do not water your dahlia until it you see it coming up (about 1-3 weeks). Otherwise, it may rot. Exceptions to this include very hot climates or very dry soils, where you should water only a little to activate growth. It’s okay if it rains. Be sure to protect young dahlias from slugs using your favorite slug prevention method (I use Sluggo®).
Any dahlia can be grown in a large enough pot, at least 2 ft (61 cm) deep and 18 inches (46 cm) wide. It will require extra watering, fertilizing, and staking. Shorter varieties do best.
Once your dahlias begin growing, they will require deep watering about every 2-5 days (more or less, depending on the weather/climate).
WEEDING AND MULCHING:
Dahlias should be kept well weeded. Mulch is recommended for preventing weeds, pests, and conserving water. I use bark chips, arborist chips, herbicide-free straw, saw dust, or similar (remember, compost is not mulch).
When a young plant has just four sets of leaves, pinch or cut back new growth above the top leaf node to encourage a shorter plant with more branches and blooms.
The more cut flowers you harvest, the more cut flowers your plant will produce! Also, removing old blooms will encourage the plant to continue to bloom.
PEST AND DISEASES:
Contact your local Master Gardener Program or Extension Agency for regionally specific advice on how to protect your dahlias. They can be susceptible to earwigs, cucumber beetles, Japanese beetles, spider mites, snails, slugs, viruses, thrips, powdery mildew, crown gall, botrytis, smut, or leaf spot. Maintaining healthy soil fertility (soil testing recommended), watering consistently, planting additional flowers that attract beneficial insects (like parasitic wasps), maintaining sufficient air circulation, and sanitizing tools can all help prevent the spread of pests and diseases.
Fall and Winter Care
DIGGING AND STORING:
Tubers have thin skins and will rot or freeze easily. They’re only hardy down to about 20 °F (–6.7 °C). It is important for dahlias to experience one mild, killing frost, so the leaves can die back (turning brown) and allow the plant to transition into dormancy. Digging and storing is the only way to ensure that your dahlia will survive in cold climates. Carefully dig up with a shovel or digging fork and shake the soil off. Store somewhere between 40-50 °F (5-10°C). They store well in bins, boxes, or crates filled with slightly dampened wood shavings, sawdust, vermiculite, or similar. Do not store in completely sealed containers or bags, otherwise they may rot.
Dahlias can be divided in the fall or spring. It is best to divide them every 1-3 years. An easy way to divide dahlias is to split the root center into halves or quarters, keeping in mind that new growth comes from eyes located where the tubers connect to the stems. After dividing, you’ll have 3-10 more to plant or share!
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