7 Causes of Dry and Shriveled Dahlia Tubers
Whether digging up dahlia tubers in the fall or pulling them out of storage in the spring, you never want to find them shriveled, dry, or shrunken. Learn what causes these symptoms to better prevent them in the future. Seasoned grower Jerad Bryant shares the seven most common causes of dry and shriveled dahlias.
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Dahlias are perennial flowers that grow from large, tuberous roots that look like sweet potatoes. These roots allow for easy storage, as you can dig them up and keep them safe throughout the winter. Dahlias are marginally frost-tolerant, growing well in the ground from USDA hardiness zones 7 through 10. Some species tolerate the cold better than others.
In cold regions, growers pot up their dahlias inside during late winter for transplanting after the last average frost date. The head start on the growing season allows them to bloom before fall and winter frosts arrive. Dahlias are late summer bloomers, and they need a long, warm season to produce their large, intricate flowers.
Sometimes, the dahlia tubers become dry and shriveled in the ground as they’re growing. This could be due to warm weather, a lack of moisture, or diseases. Other times, they shrivel during their indoor stay through the winter. Find out what’s causing the issue, and you’ll be able to decide on a viable solution.
7 Causes of Dry, Shriveled Dahlia Tubers
These seven common conditions can lead to shriveled, weak dahlia tubers. Prevent them from occurring to avoid poor performing plants, or try to stop them if they already are. It’s okay if your dahlias are already showing signs of shrinking, as there are some easy ways to help fix the problem. Without further ado, here are the seven causes of dry, wrinkly dahlia tubers.
Improper Storage Conditions
This is one of the leading causes of wrinkly dahlia roots. Proper winter storage is key in keeping these flowering plants happy and healthy until the growing season. They need some humidity, though too much moisture will lead to mushy, rotten roots.
The best way to overwinter dahlias is by using a protective and absorbent material to store them in. Things like sand, coarse vermiculite, and coco coir are ideal. After digging, washing, and drying the tuberous roots, you’ll place them in one of these materials and stow them in a cool location, like a garage or basement.
Drying the tubers for too long during the digging-up process is another way they shrivel. Without the soil’s protection, they dry and wrinkle quickly aboveground. Keep a watchful eye on your dahlias during the overwintering process to catch them before they dry too much.
Low Moisture
Low moisture or humidity—both during the growing season and the overwintering period—can weaken your dahlia stock, causing tubers to become dry or shriveled. Whether they’re actively growing or dormant in the off-season, dahlias require protection from drought.
Outdoors, dahlia plants appreciate regular moisture when they’re actively growing. They dislike soggy soils that may lead to root rot, though they appreciate moist, fertile garden soils. Keep them well-satiated during harsh droughts or high temperatures to prevent unnecessary shriveling.
Indoors, low moisture is common in poor storage conditions. Not covering the roots with enough sand or using a porous, dry material like dehydrated peat moss can lead to shrunken dahlias. You want them semi-dry throughout winter, like a potato in your pantry.
Late Plantings
Overwintering dahlia plants are still alive, though they look dead without new growth. If you forget to pot them up on time, they may begin to rot or shrivel and dry. It’s important to take them out of storage at the proper time for your hardiness zone.
One easy way to tell is by soil temperature. It’s safe to plant these tubers once the soil reaches and stays above 60°F (16°C). For most gardeners, this occurs a few weeks after their last average frost date. Use a soil thermometer to take a reading of your garden’s soil. It also works great for sensing heat in worm bins and compost piles.
If you notice the tubers shriveling prematurely, try misting them and putting them back in storage. A little mist should help them moisten and swell to a normal size.
Hot Weather
Hot weather or too high temperatures during winter storage can lead to shriveled, dry dahlia tubers. These flowers tend to suffer if they undergo long periods of intense heat. Recurring heat waves may also lead to fewer blooms in late summer and early fall.
Ensure your plants are consistently moist during heat waves to protect them from damage. If your garden has lots of direct sunlight, consider using shade cloth or an umbrella during harsh weather. Protection from the afternoon sun helps dahlias in hot zones.
In indoor cold storage, the tuberous roots require temperatures between 34-40°F (1-4°C). They’ll grow if it’s warmer, producing shoots in winter. Without dirt or moisture, the budding roots may weaken and die during the storage period. Ensure they stay cool in the optimal range to prevent unnecessary drying and shriveling.
Dry Soil
Like high heat, arid soil leads to similar drying effects in dahlia plants. Absorbent storage mediums, like wood chips or shavings, also cause these symptoms. Prevent them by maintaining proper moisture levels in storage mediums and garden soils.
If you choose to use wood shavings or dry peat moss for storing dahlias, you may have to mist the tubers if they show signs of shrinkage. It may be better to use other more protective mediums like coco coir, sand, or coarse vermiculite.
Outdoors, avoid letting the soil dry completely. When your dahlia’s leaves and blooms look weak and limp, the plant is thirsty. Watering once or twice a week during the summer months should be enough, though your plant may need more or less depending on your garden’s climate.
Diseases
Though uncommon, diseases and pests may target your dahlias. They often appear if the plants are already stressed from environmental factors like dry soil, low water, and too much or too little fertilizer. Fungi, bacteria, and viruses may infect the plants, the tubers, or both!
Crown gall disease is a common bacterial infection. It causes large, knobby outgrowths on the crowns of the tubers where new stems sprout. The lumps tend to be a light brown color that looks different from the rest of the roots. It has no treatments and rapidly spreads, so be sure to discard infected specimens before they spread the bacteria to nearby varieties.
Pests
Insect pests target dahlia foliage, while large mammals attack the roots! Voles, moles, gophers, and mice may dig underground and eat your precious dahlias. You’ll notice the plants are weak during the growing season, and when you dig them up in the fall, you’ll see bite marks with large wounds on the tubers.
Growing dahlias in raised beds with a steel mesh screen underneath the bottoms is one way to keep these pests away from your tender flowers. The metal screen prevents them from boring up into your beds.
Trapping is another solution, though it involves trapping and relocating multiple animals. Consider preventing their return with steel mesh instead of harming the local wildlife.
Key Takeaways
- Dahlia root systems need to be semi-dry during winter storage. If they shrivel, mist them and place them back in storage, repeating this as necessary until they’re healthy again.
- Proper overwintering is key to successful dahlia growing. Learn more in this step-by-step guide from master gardener Liz Jaros.
- Keeping dahlia plants healthy during the growing season will prevent shrinkage and shriveling. Ensure they grow in moist, well-drained, and fertile soil with between six and eight hours of direct sunlight.
