5 Reasons You May Want to Leave Your Dahlias in the Ground for the Winter
Learn why you may want to try leaving your dahlias in the ground for the winter and how to increase the odds they'll come back next season! Wendy Moulton will take you through the steps to ensure successful flowers in spring and summer.
Contents
In certain circumstances, leaving dahlia tubers in the ground would be better and less work than lifting them, storing them, and planting them again the following spring. The first and most important thing to consider is your climate. In USDA zones 8-10, dahlias can be left in the ground over winter with no issues.
However, in colder areas, zones 3-7, where temperatures get below 21°F (-6°C), dahlia tubers will freeze. They cannot survive the winter, so it’s best to lift and store them just before the first frost.
The other reasons are the soil conditions. Heavy, wet, clay soil is not good for tubers over winter. Dahlias will need very well-draining soil to grow generally and to survive the winter in the ground. Moreover, if you want to divide your tubers and grow more, you must dig them up.
Reasons to Leave Your Dahlias in the Ground for the Winter
Here are the key reasons why it’s better to leave them in the ground in cold climates.
Less Work
The first reason not to lift is the amount of effort and work it takes, especially if, like me, you have many different varieties and colors planted in the garden. It takes time to dig out the tubers correctly. More time is required to inspect them to ensure they are not damaged or diseased, then wash and dry them, label them, and store them appropriately.
When the stems and leaves have died down, cut them to ground level. The stems should stay on the plants as long as possible without causing pests and diseases so that they can still direct nutrients into the tubers and be ready for sprouting in spring.
Add a good layer of mulch to keep them warm – compost is a good choice – and leave them to overwinter in the ground.
Early Blooms
Typically, tubers left in the soil will start sprouting early as soon as the soil warms up and produce flowers earlier than ones that still need to be planted. New plants will take a little time to acclimate to the conditions before they are settled and ready to grow.
Leaving them in place means earlier blooms and a longer flowering season to enjoy.
Robust Plants
As these plants grow, their underground root system also multiply and become larger masses with more opportunities for growth points. By keeping them in the ground, you effectively produce more stems, which will also give you more robust plants and flowers.
New dahlias will take a few seasons to get strong and vigorous, unlike those that stay in the ground and build their strength every season.
Less Pinching
By leaving them in the ground, your plants will be strong and produce more flowers generally. This means there is a limited need to pinch out the growing points. This process makes the plants bushier and stronger. You may not even have to pinch out at all.
No Proper Storage Options
In certain circumstances, it may be best to leave them in the garden because of the possible losses during storage. Not everyone has a cool, dry place to store tubers, and even then, there is a chance that the they can become infected or contract a fungal disease, which may wipe out your entire collection. In the right climate, overwintering them in the soil would be better than trying to store them.
How to Overwinter Dahlias In the Garden
There are some extra points to consider when planning to overwinter your flowers. Firstly, at the planting stage, add extra space between plants if you are planning on leaving them. As dahlias grow, their underground mass becomes bigger, producing more stems, so it’s important to space them appropriately to allow airflow between plants and avoid potential fungal diseases.
Plant new tubers a bit later in the season so you have a longer flowering time. The newer ones will flower after the overwintered ones, giving you extended flowering time.
Keep watering and fertilizing throughout the growing season and as they start to die down. Once you have cut them back and covered them with a good layer of organic mulch, stop watering and feeding and start again in spring. Consider covering your bulbs with straw or plastic in colder areas for extra warmth.
Dahlias planted close to a house have the extra warmth they need from the house being warmed. Planting dahlias in containers also makes it much easier to keep warm over winter, by moving them into a greenhouse, a sheltered spot in the garden, or indoors.
Some varieties will overwinter in the ground, and others will not. You can only figure this out after you have grown and overwintered them, and they fail to come up again in spring. Experimentation is the nature of gardening, and if you consider that a single plant is about the same price as a bouquet, it is worth it even if you only get a season out of them.