Tip Tuesday: Dahlia Post Season Care

I’m going to try to make this a running theme, Tip Tuesday, to share information that I’ve learned along the way so that you can apply to your own garden. Everything I’ve learned, I learned from someone else or learned it the hard way by trial and error.

This week we will discuss post-season dahlia care. In my zone 6a/5b climate of north central Pennsylvania, it’s too cold to just cut them down and allow them to fend for themselves over the cold winter. They need to be dug out of the ground and stored properly in order to re-plant them and get blooms the next season. If they freeze, dry out, or rot, they will die. No flowers for you next year! Below, I’ll go through my process as well as my suggestions for home gardeners.

If you ask any grower how they dig and store dahlias you’ll get as many answers as growers you ask. There is no wrong or right way to do it successfully. A lot depends on your region’s weather, humidity, etc. I’m going to speak only on my area and what I’ve had success with.

Now, with that being said, I AM doing a huge experiment this winter in trying to overwinter some of my dahlias. I’m literally going to leave about 40% of my tubers in the ground and dig the rest up to split. Even if it fails miserably, I’ll still have the same amount of tubers to plant next year since dahlias generally produce anywhere from 2-20 tubers each year. Any varieties that were in a trial phase or that I want to increase in stock were all dug up.

We shall see! The plan for those that are left in the ground is to cut them down, cover very thickly with approximately 1.5-2 ft. of straw and then cover with a silage tarp. The tarp is key to keep out excess rain and moisture which can make the tubers rot and die.

Now on to normal winter care:

I dig my dahlias after at least one hard frost. Two is nice. This turns the leaves and stems black as soon as they thaw out. (**this year we had a very late frost, technically if your tubers have been in the ground for 120 days, they are fine to come out even if you haven’t had a frost).

I cut the stems down as I’m able to dig. If you have no rain in the forecast and you know you’ll have time to dig them all up, go ahead and cut them all down. For me, I grew around 700+ this year so I need to do it in phases. I cut as many as I can dig in that day and leave the rest until I’m ready to dig again. This prevents water from gathering in the hollow stems and rotting the tubers from the inside out. I have had it rain into my cut stems and they were just fine but I like to prevent as much user error as possible.

If you grow any number of dahlias and care about which variety is which, be SURE to label them while they’re still blooming to ensure accurate varieties. Once they freeze, they’ll all die and look the same. I am the ultimate failure with this so next year my goal it to label EARLY!!

To dig: use a potato fork or a pitch fork. You’ll do less damage to the tubers versus using a shovel. Start approximately 10-12'“ away from the center stalk and sink the fork tines into the ground. Pull back and lift the soil to loosen while also lifting the tuber out of the ground. Depending on your soil, this may be simple or difficult. The more clay in your soil, the more difficult it will be. Go around the stalk as much as necessary to gently lift the tuber and release it from the soil, give it a gentle shake to knock off the dirt and move on to the next!

I store my freshly dug clumps in bulb crates in the interim before I clean and split them. You can use a plastic tub or any bucket you have laying around.

** As a home gardener, I recommend a super simple storage method. If you only have a handful of plants, store them as whole clumps (or split in half or quarters) and store with the dirt on them in a bucket or plastic tub. A lid set ajar should be fine to regulate the humidity, the dirt does a great job of that. Place your container in a cold area that does not freeze. A cold basement is perfect or an unheated garage.

Again, since I grow so many and split them to increase my stock, I do things a little differently. After digging, I clean all of the dirt off with the hose. I try to avoid the stalk to keep water from rotting them from the inside out. Cleaning them helps me to see the “eyes” which are a little nub that will turn into the stem of next years plant.

When splitting dahlias, you have to have a tuber that has an eye or it will never grow. Even if it’s the biggest, plumpest tuber ever, no eye = trash.

Rather than reinvent the wheel, I’ll link my favorite source for splitting dahlias if you are interested in doing that.>> The best splitting guide there is. << It helped me so much when I was learning. The next best way to learn is JUST DO IT. With practice, it becomes easier.

After my dahlia tubers are cleaned and split, I store them in plastic tote tubs and use agricultural grade coarse vermiculite that is a bit damp. I lay down some vermiculite and then layer tubers single layer at a time with vermiculite in between. I put the same varieties together but if I have a small amount I will combine them. The key is to write the variety name directly on the tuber itself with a Garden Marker. This will prevent any confusion in the spring.

Storage temperatures need to be above freezing but below about 50 F. If they’re too warm they won’t go into dormancy, if they freeze they’ll die.

Check on them occasionally to ensure they are not too dry or too damp. If too damp and they haven’t rotted, remove the lid for a bit to let the moisture evaporate. If too dry and starting to shrivel, mist with water and close the lid.

If any have completely shriveled up, rotted, or turned to mush, removed them immediately and throw away.

Stay tuned for more Tip Tuesdays. One of which will be planting dahlias in the spring!

If you have ANYTHING you’d like me to discuss, shoot me an email or a message on social media! Thanks for reading along!

-Emily