Starting Tubers Ahead Of Planting
If you pot up the tubers about 6 weeks ahead of the frost free date in your area, you will have nice sized plants to plant out when the time comes. This will advance the first blooming date by about five weeks, which is a great thing to do! Dahlias will keep blooming until frost so lengthening the season up front will give you lots more blooms.
I suggest you use pots about 6″ or more in size, and line each with two sheets of newspaper, leaving the paper above the pot’s edge. Keep the soil just slightly moist, but not wet. When you plant them out, remove the newspaper from the pot keeping the soil ball intact, causing the least disruption to the root system possible. Plant it, paper and all, so that you have three or so inches of soil above the tuber when in the ground. It need not be that deep in the starter pot, especially if it is a large tuber.
Planting Tubers
Tubers are planted horizontally preferably with the sprout pointing up. Remove about four inches of soil, add some slow release fertilizer to the soil, and set in the tuber. Cover with about three inches of soil. Do not water the tubers at this stage unless you have drought conditions. There is enough moisture in the tuber to nurture it until it breaks through the surface of the soil. Then water as you would any plant.
A prime tuber is the size of your thumb up to your wrist. This size will have enough food and moisture to feed a sprout, but not so much that the tuber is slow to send out roots
Staking
I am ‘real estate’ challenged here, so I want my plants to grow tall rather than wide. I always stake my plants, and even prune a little to encourage height. If you have several sprouts from one tuber, it will naturally take a bushier shape. If you reduce it to one strong sprout, it will tend to grow taller. Some of the dinnerplates can get a stalk the size of your wrist, if reduced to one stem.
The need to stake also depends on how sheltered from the wind your location is, and how vigilant you are with fertilizer and picking. Extra potassium rich fertilizer will strengthen stems to some degree, but I haven’t found it to work as well as staking. Those big blooms are so heavy, I lose some to wind or rain even when I am constantly tying and wiring. My location is wide open to the wind. You are best to put in a stake when you plant (one or two rebar work well), so that you don’t risk piercing the tuber when doing it later.
Pruning and Fertilizing
I usually remove the bottom few leaves once the plant gets to be around 18” high, so that the dahlia continues to grow taller. This makes it easier to apply fertilizer as a drench close to the base, but the soil will dry faster close to the plant. The buds form in groups of three and if the side buds are removed the centre bloom will be much improved. Not only will it be much larger, but the stem will be longer and stronger. I like stems 12” to 14” long and with some varieties this means removing as many as five buds from along the stem.
A balanced fertilizer (such as 20-20-20) can be applied when the plants appear until buds set. Then switch to a fertilizer high in phospherous (such as 8-22-10) to promote blooms. Never use grass fertilizer (high first number) as you will get very few blooms if any.
Picking and Reviving
Keep blooms picked to ensure your plants keep blooming at their best. Dead head if the blooms are passed their best. The spent blooms attract bugs and look messy. Pick blooms in early morning or when cool weather and keep them out of direct sun for longevity. If they wilt, they can be revived by snipping an inch off the stem and placing the stems into an inch of boiling water in a plastic or metal pitcher (not glass as it cools too quickly). Leave for 15 minutes and they come back to life.
Disease, Animal, and Pest Control
Neem is a great organic solution to insect, animal, and disease control. It can be bought inexpensively at East Indian and African grocers, or some bulk food stores. It is also available online. It is not available at nurseries or big box stores as it is not approved for this purpose in North America. It is commonly used in the rest of the world however, and is extremely safe – even edible. Research it for more details. It can be applied combined with fertilizer. In the same sprayer. Pure neem is the least expensive. It is often the active ingredient in foliar sprays, so leaves are lush deep green colour with use. Rabbits don’t like the taste, but it needs to be reapplied often to deter them.
Harvesting Tubers
Frost will end the blooming season for dahlias. This is usually the second week of October in Ottawa. T Plants become droopy and dark, and the blooms ruined when frost hits - a sad day indeed. After about a week, cut off the foliage and compost it, leaving 4” or 6” of the stalks above ground.
The same day, or it could be several days later, dig with a deep shovel about 14” away from the stalk, all the way around the stalk. Dig deeply, as the tubers may have grown downward, and you don’t want to break them or cut through them. If you dig your tubers after a week or more from when the frost hit, there may be new sprout nodes visible on the tubers! They are usually pink or whitish. These bumps disappear back into the tuber after the tubers are dug and aren't visible again until spring.
When the stalks with the tubers attached are free from the soil, tip them out of their hole, laying them backward onto the stalks. They may be very heavy depending on how big the plant was, how many tubers have developed, and what your soil is like.
Gently knock the soil away from the tubers and lift the system intact. Don’t wash them. The thin film of soil is a good protection through the winter. Take the clump to your garage or somewhere cool but not freezing, where it can dry well for a day or two. They will likely be brittle and will break easily so be careful.
Storing Tubers
If your clump had several stalks, you can separate it somewhat after it is dry to the touch. Take hold of one stalk in each hand and pull to separate them from each other. They will naturally break apart in the best place. Do this for each stalk. It is really important that you don’t break the tubers off the stalk they are connected to, so be gentle.
You likely planted one tuber, or maybe a small clump in the spring. Find this original ‘mother tuber', remove it from the clump and discard (compost) it. It will be a slightly darker colour than the rest or will have a different root system than the other tubers. It may have a different skin texture, or be soft, or even have started to rot away. By removing it now, you will increase the chance of your tubers surviving winter, as most rot starts in this old tuber during storage. The mother tuber will never grow good blooms again, although it may grow roots and a sprout. Just get rid of it.
Cut the stalks back to a couple inches above the tubers. Don’t cut them too short, as this is where the new sprouts are likely to develop. If the clump is still huge, you may want to further divide it to get it compact enough to store easily. Do this by splitting down into the stalk with your pruners and keeping a portion of the stalk attached to a section of the tubers. They are something like a clump of bananas, all attached together, but each with a portion of the flesh where they grew on the tree.
Get a box, or bin, or plastic bag that is just a little larger than the clumps of tuber you have now. Buy some vermiculite from a garden supply store, and completely cover your clumps leaving no air pockets. Leave the box or bin or bag open for air circulation, label the variety, and put it into a root cellar or cold storage or unheated bedroom – anywhere just above freezing. The vermiculite can be reused the following year. I like to use banana boxes lined with plastic, filled quite densely with tubers. The vermiculite is poured over, the box shaken, and more vermiculite added to fill it.
Tubers will freeze in an Ottawa garage, and a heated basement is not cool enough to store tubers. They need 40 to 45 degrees Fahrenheit all winter long. Put something between any cement floor and the tubers, as concrete draws the moisture and they will shrivel. Several inches of newspaper or cardboard, or a board will suffice.
Check on the tubers occasionally through the winter. Throw out any that are moulding. If some are shrivelling, sprinkle water into the box.
Dividing Tubers
In March or early April bring them into room temperature and they will start to sprout in about a week. Keep the vermiculite around them during this time, but you can check them daily for sprouts. If you take the vermiculite away, they will likely wither, shrivel, and dry out.
When the sprouts come, they will be along the original stem where they join each other. Take pruning shears or a box cutter and separate the tuber with its sprout, from the clump. Or you can leave a few small tubers joined as a small clump to be planted together. If it is hard to cut through, a good trick is to put one blade of your sheers into the old hollow stem and cut down through the stem keeping the sprout attached to the tuber. If a sprout breaks off when you are dividing them, don’t worry. Chances are good it will grow a new sprout in the same place, in a week or two. Put the newly divided individual tubers back into vermiculite to store until planting time, preferably somewhere cool so they won’t grow too much until you pot them up or get them planted after frost danger has passed. You can divide your tubers before they begin to sprout if you recognize the ‘eye’ or node where the sprout will develop. Some people divide their tubers in the fall, but I have had better luck dividing in the spring.
Half a dozen or more tubers may develop from the one original mother tuber you planted. About three quarters of the tubers you store will be viable and produce sprouts in the spring. Don’t expect them all to grow. A tuber with two sprouts will have two stems on the plant and be bushier. A mistake many people make in trying to keep their tubers over winter is breaking their necks! Without that connection to the old stalk or stem that joins them together, they won’t sprout, although they will grow roots.
It is amazing when you consider the beauty of a dahlia plant all tucked into a tuber. Such potential in a perfect package - well worth the effort of trying to overwinter your favourites. And there is nothing like the feeling of seeing your old friends starting to bloom again the next summer, having made it through a Canadian winter to celebrate summer the next year!
