Fall is always a busy time of the year for northern gardeners, and that’s no exception here at North. Over the past few weeks, we have been inundated with questions about the removal and winter storage of tender summer-flowering bulbs like cannas, dahlias, callas, gladiolus, and anemone.
I felt that instead of answering each question individually, it would be best for us to provide our readers with an article on the process and answer all these questions in one shot. For the most part, the process is the same between various types of bulbs, but when necessary I will cite the question and the particular difference as warranted.
Many of you have written similar to this question, “We are going to winter over dahlias this year. When is the best time to dig the bulbs – before or after a frost? They are all still blooming gloriously now and I would hate to dig them while still blooming!”
I knew this answer intuitively, but I wanted to verify my information with a colleague of mine, a renowned horticulturist. He concurred that unless the temperature really gets well below freezing for a long period of time, it really doesn’t matter when you dig them out in our colder climates.
It is only in the southern areas that it is important to dig the bulbs from the ground to give them the sufficient dormancy that they require.
We Northscapers are blessed with long winters and therefore have the luxury of time to over-winter bulbs. So if they are still performing, you are OK to leave them be and wait until they get browned from a light frost before you start yanking them from the ground. See; even experts have to get a second opinion from time to time!
Aside from wanting to know when to lift tender bulbs like dahlias from the garden, many novices to this type of gardening ask, “I am trying my hand at dahlias and need to know… how to store them so I can put them out again next year. I’m told they will bloom for me if I do this.”
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And Judy, you are correct in your understanding, or we wouldn’t be talking about this subject! Any summer bulb like anemone, tuberous begonias, cannas, callas, dahlias, gladiolas, tigridia, etc., will require lifting and storage in a cold cellar or cool dark place through the winter months to allow the bulb to rest before being replanted in spring. The process is relatively the same for all of these types of plants, and it goes like this;
Preparing Bulbs for Storage
1. Carefully dig up the roots (tubers, bulbs, or corms, as the case may be) from the garden, taking care so as to not cut through a bulb. Should a bulb be cut, discard it; it will likely not survive.
2. Label the plant with a variety and types of bulbs in waterproof permanent ink on a tag tied to the root. This is extremely important if you have different varieties of a given bulb, or if you are a novice and cannot tell the difference between canna or a dahlia tuber by sight alone.
3. Remove excess soil gently. In looser sandy soils this will be easy, but where clay is your predominant soil type, I generally would leave them in the sun for a day or so to dry off (but not dry out!!). This makes the soil brittle and easier to clean from the bulbs.
4. As you lift the bulbs, you will notice in cases such as cannas that they may have multiplied. You may want to divide the tubers at this time. This can be done in the spring as well, but if you are dividing now to share with friends, ensure that there are at least 2 to 3 eyes (sprouts) left on each tuber. This will help guarantee successful germination in the spring.
5. The next step is to set the dormancy bed. Find a wood or cardboard box, and line it with a relatively dry storage medium of peat moss, sand, or sawdust. Plastic containers are not porous enough and may trap too much moisture, resulting in the bulbs developing a fungus or mold, which would have adverse effects on the germination and the success of the bulb next spring.
Likewise, too wet a storage medium will result in the same. An extremely dry storage medium may absorb the moisture from the roots and thus cause the root to fail or just dry right up.
6. Lay the bulbs in the lined container in a single row. Do not double stack rows or mix plant types.
7. Add just enough of the storage medium to cover the bulbs.
8. Store the open container in a cool dark location in the basement, garage, or better in a root cellar, away from radiators, damp areas, or leaky walls. Any of these factors may ruin the bulbs during their period of hibernation.
Other Related Questions
We then come to specific situations such as that experienced. She asks, “I am interested in storing the bulbs of my caladiums for the winter. What is the best way to do this? I’ve tried in the past to store them in peat moss in my cool cellar but they seem to just shrivel up. Do they need to be watered?”
I would advise checking to see if either steps 5 or 8 are possible factors. Caladiums and many other shade plants do better being stored in sand or sawdust as these mediums will retain a bit more moisture than peat moss. As well, most modern homes are heated with gas heat, and this can be very desiccating to plants through the winter.
Bulbs stored in too dry of a location or medium may experience the desiccation I described earlier. If this is not the case, or if this is impossible to do because of circumstances, then I would suggest placing damp (not wet) newspaper over the tuber before covering it. Or, slightly moisten the storage medium with water from a spray bottle.
The final common question on this subject comes. She asks, “I have some summer bulbs (dahlia, gladiolus, anemone) which should have been planted early this spring; but I did not receive them until the first week of August.
Would you suggest I place them in the ground now (all but the Dahlia bulbs) or wait until next year? If I store them, please suggest how. Won’t they dry out after two winters out of the ground?”
As long as the bulbs have been kept cool, then you can continue to store them through a second winter. However, there is a good chance that they will not perform as well as if you had planted them immediately upon receiving them and then lifting them even though they might not have bloomed.
Though dormant, the starches which are stored in the roots to promote growth and bloom, begin to deteriorate. Think of bulbs, tubers, and corms like batteries. Even if you do not use them, they will lose some of the energy that they have stored due to cellular breakdown.
In the case of bulbs, the flowers may not be as large or as abundant as hoped, but the bulb still may come through.
I hope this has answered many of your questions regarding lifting and storing summer bulbs through their much-needed dormancy of winter. In early spring I will follow up with a second part to let you know just how to start these little treasures up for next year’s blooms.
So until next time, and likely after a great deal of digging up your gardens… Happy Harvesting!