Protecting your Dahlias against the Winter frost is essential to ensure repeat blooms year after year. Dahlia bulbs are non – hardy plants and their bulbs will perish in Winter frosts if they are not covered or brought indoors. Dahlias are hardy down to temperatures of – 6°C but anything below that can be detrimental to the plants. For this reason, it is recommended that you lift your dahlia bulbs in Autumn & bring them indoors over the Winter months.
The best time to lift your dahlias is just after the first frost. Wait for all the foliage to die back on your plants before lifting. Once there are signs of early frost damage such as the blackening of their foliage, you can get your garden fork out & lift the bulbs.
If you feel you live in milder climates where temperature rarely drop to below -6 to -10°C then you can consider leaving your dahlias in the ground & instead cover your crop with layers of mulch & straw.
Ideally a 3″ to 6″ layer of mulch would be needed to protect your dahlia bulbs throughout the Winter months. But, if for example, you live in the middle of Ireland, where temperatures are likely to drop below -10°C at some point during the Winter months, then the advice would be to lift & store your bulbs indoors.
The process is quick & easy. Firstly we suggest to always mark the spot where you plant your dahlias, as by the time you get around to lifting them, all their foliage could have died back making it difficult to figure out exactly where underground the bulbs sit. If the foliage has not fully died back, then now is the time to cut away the remaining leaves.
Use a 4 pronged digging fork to lift your dahlia bulbs. Start by carefully forcing the fork down into the ground about 30cm (1 foot) away from where the bulbs are located in the ground, then gently prise up the clump by levering the fork in the ground.
A slow back & forth motion will ensure the least amount of damage to the bulbs. If the clump of bulbs is quite large, which can be the case if you only lift your dahlias every few years, then work your way in a circle around the clump lifting it on all sides. Take care not to damage or bruise the roots as these will quickly rot when in storage.
Once lifted, remove any heavy soil be hand. Place bulbs in a cool & well ventilated location to dry off. This can take about 2 weeks. Place bulbs upside down on a flat surface.
Once the bulbs have dried, you can store them for the Winter months. The aim now is to keep the bulbs dry & free from frost. If your shed is prone to frost then cover the bulbs with layers of straw or you can store your bulbs in a greenhouse. To keep the bulbs in top condition & dry, you can store them in sand, grit, dry compost or vermiculite.
Once the weather warms up again in Spring, you can replant your dahlias out in the garden. Again label & mark the location of your bulbs. This is a good time to also condition your soil by added well rotted farm yard manure & if the soil is prone to getting wet, you can also add a hand full of potting grit onto which you can sit your dahlia bulbs.