I ordered some hardy perennials that are being shipped across Canada, from BC to me in Toronto. Unfortunately, I found out after the fact that the nursery has a bad reputation and I am concerned about picking up jumping worms. I can’t trace the origin of the plants as the nursery is unresponsive to such inquiries. The plants have begun to arrive, and I am not sure how to overwinter them, as I don’t want to plant them in my garden without making certain they don’t have any pests. I’m also not sure how to test for jumping worms at the end of the season. I was thinking about unpotting the plants to the bare roots and chucking the soil, but I’m not sure how that process will go if the plant is dormant and I can’t plant it outside right away after that.
What would happen if I were to keep (for example) a potted Rodgerisia pinnata (USDA zone 4-9) indoors at 17-18C for the winter? Should I try to dig it out and repot it first, or let it ride out the winter and then bare-root it in spring? My other option is to overwinter in the unheated garage, but I fear that will provide little protection from the coldest temperatures we get here in Toronto. Sorry for the complex question, there are a few variables here to consider.
Dear Gardener, this is an interesting and engaging – and very complex — problem. We have tried to break it down into its component parts, but many of your questions have optional answers. We hope that this is helpful to you.
Firstly, please may I offer our sympathies! Spending a lot of time and money choosing and buying your perennials, and then finding out that they did not come from a reputable nursery, must be most distressing.
The first issue must be what to do with your plants that you suspect may have pests in general, and maybe jumping worms, in the soil. Since your plants are now dormant (end November), your idea of repotting them is excellent. Take them out of their pots, bag all the old soil, wash the bare roots, and repot the plants with fresh soil. Just make sure that you are giving each plant a lot of fresh soil (maybe give them pots slightly bigger than the ones they came in). The plants will be able to better survive the cold if they are well insulated with soil.
However, repotting can cause stress. You could leave them in their current pots and bare root them (wash and give them fresh soil) in the spring.
If you are going to reuse the pots that the plants came in, sterilize the pots with warm water and diluted vinegar or rubbing alcohol. This will make sure that the pots are not harboring any fungi or bacteria that are not immediately visible. Make sure you do likewise with any garden tools you are using.
As to the issue of potentially importing jumping worms into your garden. What a horrible thought! Your concern is real, although at this point in time, there are no reports of jumping worms in British Columbia (where you got your plants from). This is currently an east coast issue, but will likely spread. Although I would not be overly concerned about jumping worms coming to you from BC, pest and disease movement is always a potential issue.
Since you brought up this problem, Halton Region Master Gardeners have an excellent handout on the topic of jumping worms. Particularly relevant is that they strongly recommend root washing and using fresh new soil.
Moreover, the Halton factsheet warn that many municipalities do not allow you to garbage old soil, in case of importing pests, disease, and jumping worms. What is recommended is that you collect and store the old soil in a black plastic bag for the winter. In the summer, put the bag of soil out in the sun for at least three days. The soil needs to be solarized to a minimum of 104°F. The heat will kill the eggs and/or pathogens, and should be safe to re-use in the garden.
The University of Maryland has further guidance on jumping worms with some excelling photographs. The worms can be identified by their manic behaviour and also from their typical pale band (called clitellum). The most important point they make, is that even if you lay out the soil from your containers on a tarmac to inspect the soil for worms (in order to catch and kill them), you will probably not find them at this time of the year. Jumping Worms have an annual life cycle; the adults die after the first hard frost; the next generation survives the winter in the form of cocoons (egg casings). They hatch and survive when the soil temperature is consistently about 10˚C. They develop into full-size adults in about 60 days.
The University also recommends that if you are buying potted plants, check for granulated soil on the top of the pots since that is an indicator of jumping worms. Also, they recommend that people buy bare-root plants. This is good piece of advice going forward for future purchases.
Now for the overwintering question, may I suggest putting the plants (repotted with lots of soil) in a protected area in your garage. Cover all the plants with something like straw, peat moss, leaves or compost. The temperature in a garage is warmer than outdoors and the plants will not be exposed to the drying winds. Check the plants for moisture a couple of times during the winter.
An alternative to the idea of storing them in a garage, if you still can get into your garden, is to dig a trench in a protected area and set in your plants (that have been repotted) with a covering of evergreen boughs, straw or mulch for winter protection.
The Master Gardeners have previously answered a question on plant hardiness zones, which compares the Canadian with the USDA plant hardiness zones. Toronto is in Canadian plant hardiness zone 6a to 7a, but is a US zone 5. Your Rodgersia pinnata, which is registered as winter hardy for USDA zone 5 and above, should be fine overwintering in your garage, and therefore digging it up while you can, cleaning it off, and repotting it with fresh soil may be a good idea. This site has more information on USDA zone 5 temperatures.
I wish you good luck and hope you can get all of this done before the real cold of winter settles in.