Dahlias: Harvest, Divide & Store
Dahlias aren't difficult flowers to grow and in my opinion are one of the most satisfying to see bloom. For all that beauty though, they are rather labour intensive on the other end. You need to dig them up, divide and safely store them over the winter. For me, all that hard work we put into growing and caring for them makes them closer to my heart and the flowers even more beautiful. While there's a lot of labor involved, your work is richly rewarded when those babies finally start blooming. And blooming. And blooming.
But when the frost finally does come, it helps to have a game plan for harvesting and storage. Harvesting is pretty straight forward, no matter how many plants you have (ok, within reason), but what you do with your tubers from there will likely depend on a few factors. How many plants do you have? Where will you store them? What kind of medium will you store them in? You will also want to consider how much work you want to do. Is your main goal just to get the tubers through the winter and then replant the clumps in the spring (less work) or do you want to try to increase your stock as much as possible and divide as many as you can (more work)? It sounds like a lot of decisions to make, but with a little planning, you'll be ready for fall!
Before I continue, let me say this: there are many ways to harvest and store your dahlias and lots of different opinions on the best way to do so. I'm not suggesting that we have the "best" way, but it's successful and works well for us. Your main objective is to have your tubers make it through the winter. I've heard all kinds of stories of people who don't pay attention to when they harvest, then chuck them in the back of a warm closet and don't think about them until spring. Well, that may work for them, but my goal here is to help you have the best chance of being successful. Learning some good practices will give you the tools to make the decision for yourself.
In Canada, almost all gardeners will need to lift their dahlia plants and store them to protect them from frost (or rot in some cases, like coastal BC). Learning the right time to dig your dahlias can help you successfully shepherd your tubers through winter. Typically, you'll wait for a hard frost before you start digging. However, this isn't a requirement- it's just a good rule of thumb. There are some locations that rarely get a hard frost, or years when you may have a very mild fall and won't get a hard frost until the ground is covered in snow. Or, you may have lots of tubers and need more time to get them processed before the weather turns. In that case, you'll want to wait until late fall and then cut back your plants. Just leave yourself plenty of time to dig all your plants and safely get them into storage before the weather makes it too difficult. Before your plants die back, be sure you have everything labeled! A good method is to write the name with permanent marker on flagging tape and tie it to the bottom of the stem just above the ground.
Whether it's frost or the calendar guiding you, you'll want to cut back your plants almost all the way to the ground. Use good loppers and cut the whole plant down, leaving just a few inches of thick stalk above the ground. Then, wait a week or so after a hard frost (or cutting back the plants) to start digging. Tubers dug too early in the season tend to not store as well and be more prone to shrivelling. We use a garden fork to loosen the soil all around the plant and then carefully lift the tubers from the ground. Go slowly and use caution. Then, if your soil allows, gently shake or comb away the loose dirt from the clump, being careful not to break the tubers from the neck.
Summing it up:
1. Cut back the whole plant with good loppers, leaving a few inches of thick stem for a handle, after the first hard frost- or in the late fall.
2. After cutting back the plant, wait about a week to begin harvesting
3. Carefully loosen the soil around your plant and lift them with a garden fork. Don't just grab them by the "handle" and pull- you can break a lot of tubers that way
4. Gently shake or brush the dirt off from around the plant
Now you're ready for the next step!
Now you have some decisions to make. To wash, or not to wash? Leave them whole or divide them? Should you divide them now or in the spring? Gah! So many decisions!
If you don't have lots of plants and have enough space, you can simply store your dahlias in whole clumps. Some people, who don't have heavy soils can simply brush off the loose dirt, cut the stem back, and store them just like that in crates, bags or boxes. Easy, peasy. You just need to make sure you have the right storage conditions- more on that later. You can then divide them in the spring or over the winter when you have the time.
Many of us don't have sufficient storage space to keep all our dahlias whole and need to break them down into smaller chunks for winter. In this case, we recommend washing them first. It just makes it easier to see what's going on and saves your clippers from getting too dull from trying to cut through dirt. Washing is simple- just use a gentle direct spray from your hose. If you're too aggressive you can damage the skin and even break tubers from the neck of the stem (which you'll learn later isn't a good thing). Wash them as best as you can, especially in the middle of the clump where you'll want to be able to see where they all attach to the stem.
After washing, we start dividing right away and then set them out to dry someplace inside where they'll be protected from frost and the elements. We dry ours on screens in our greenhouse. Then, usually after a day or two they're ready to be packed for storage. If you notice that your tubers are starting to shrivel- it's time to get them packed!
Dividing dahlias can cause a lot of anxiety when you're first learning- and even after you've done thousands, it can still be a daunting task. But, like anything it just takes practice and you'll grow more comfortable with time. Learning a few tips and knowing what to look for when dividing will help you approach the task with more confidence.
Every plant will produce multiple tubers connected to a main central stem. You can easily multiply your stock each year by dividing off each healthy tuber that has a viable eye on it. If properly cared for, each tuber will produce a whole new plant the next season with many new tubers. You don't have to divide each one off separately, but if you want to really increase your stock this is one way to do it!
When starting to divide your dahlias sometimes just figuring out where to begin is the hardest part. It can feel intimidating. The first thing we do is to remove any tubers that were badly damaged during harvesting. Then we start to break them down into manageable pieces.
My best advice here is to just dig in- don't be afraid! Using some large loppers (or we now use a small hand-held, electric cutting tool) divide the clump into smaller, workable pieces. Your goal is to break down the clump into manageable chunks, each with a few tubers connected to the main stem.
In the video below you can see how Carl just cuts right down through the centre, doing his best to avoid chopping off tubers. Sometimes it happens though. Don't worry about it- you'll get better each time. Some varieties tend to be more straightforward and some are just a huge tangled mess! Usually, when I come across those I take comfort in knowing that there are lots of tubers in there, so I may need to sacrifice a few to make the job easier.
Once your clump is in more manageable pieces it's easier to see what's going on. We then proceed to remove any tubers that are really thin and skinny (pencil width or smaller) and will likely shrivel up in storage. We trim all the long hairy roots off as well. We also remove any tubers that were broken during the harvesting or washing process. If the neck is broken and the tuber is flopping it won't be good for planting, so remove these too. Just use your clippers to snip them off.
When you've trimmed up your chunks you're ready to start dividing individual tubers, or at this point you can stow away your chunks to deal with later. One word of advice here is to make sure that you've entirely removed the old stem, this is a potential place for rot to creep in. If and when you're ready to divide, just remember that your main goal is to make sure that there is an eye attached to the tuber.
In the above example, we can see that there are two eyes and we can make a cut to separate the two individual tubers.
In the picture above you can see the arrows are pointing to three separate eyes. The one in the centre is more difficult to see, but with good sharp clippers and careful cuts you could get three nice tubers.
If you decide to wait until winter to start dividing, just keep in mind that it is often difficult to see the eyes at first. Usually letting them warm up for a few days will make finding the eyes much easier.
Another decision to be made! Where can you store your dahlias and what container and medium do you store them in? First learn the basic criteria and then you can find a spot and method that works best for you.
They can't freeze! Ideal storage temperature is around 5 degrees C (40 F), or a range of 5-10 C (40-50F)
You don't want them to rot or to dry out. Typically you want high relative humidity, around 70%
Good storage media are wood shavings (pet/ horse bedding), vermiculite, or peat moss. If using peat moss, just be sure your tubers are dry and the peat isn't too moist. Peat can hold a lot of moisture and depending on conditions contribute to rot. But lots of folks pack their tubers in peat, so it really just depends on your specific site!
You can use any kind of container, crate, bins, boxes or bags. We use plastic storage totes with holes drilled in them because in our climate we are usually more concerned with tubers drying out.
If you have perfect storage conditions, some people just store whole clumps loose in crates lined with paper.
Generally a basement is a great place to store your tubers. Your specific climate will determine how you will want to store them. Here our air is cold and dry and if storing in our basement we have to watch for the tubers drying out. This year we are storing them in our air-tight, insulated walk-in cooler and the humidity is relatively high, so we are watching for signs of mould or rot.
We store our tubers in plastic totes with large holes drilled in the sides towards the top of the bin. We use wood shavings as our storage medium, although we have also had great success with vermiculite as well. We start by adding a few inches of shavings in the bottom and then laying tubers out across the bed of shavings so they are not touching. We then add another layer of shavings to cover and keep repeating the process until the tote is full. We put only one variety in each tote and label it carefully on the inside and out. You can use the same method with any type of medium you choose- just keep layering them in and covering them up. One thing to keep in mind is that if you have many deep layers, it is more difficult to check the ones at the very bottom!
Whatever type of container you use or medium you choose (or not!) your main goal is to not allow them to dry out or to get too moist and rot. Check your tubers regularly throughout the winter, at least once a month, and see how they look. If you're using a paper bag and they seem to be drying out you could place them in plastic. If they're in plastic and your noticing a lot of dampness, you can open up the bag or tote to let the moisture escape.
You really have to experiment and find the conditions that work for you and the space and tools you have available.
All this may make it seem like this is a difficult process, but it's really not too bad! Give it a try and you'll learn as you go! Let me know if you have any questions, leave a question or comment below and I'll do my best to help.