How should I overwinter my potted clematis in Massachusetts, Zone 6a?

Question

As fall approaches here in Massachusetts USA, Zone 6a, (temperatures generally no lower than −5°F, −20°C), I am beginning to wonder what to do with two clematis plants I have been attempting to grow. I do not know anything specific to their species beyond that they are Clematis.

They are both in 6 inch pots and are about 16 inches in length. Should I plant them in the ground and find them next spring? Will they survive or should I attempt to bring them indoors? I do not have a garden shed or area other then my house to put them in.

I do not want to lose them, as it has taken some time for them to grow as big as they have.

Answer 1

There should be enough time to allow your plants to acclimate to the soil and their new home before the weather turns too harsh and freezing. If your plants are used to being outside in the sun, I'd plant them where you want them in your garden then mulch the soil heavily for the winter (straw, sawdust) and remove this mulch in the spring to allow the soil to warm. Otherwise, they need a few weeks 'hardening off' to not get burned by the direct sun. I am assuming you'll remove the pot they are in right now. Prepare their new home by digging up the area (18"X 18" and only as deep as the roots...6"?) turning the soil up, chopping chunks of soil and creating a bit of a raised mound, firming to fill holes in the mound, then planting. I'd also put a 'collar' around the stem at the soil to prevent the voles from eating the new stem. This should be wide enough and placed down into the soil and allow plenty of room for mulch snuggled up to the stem/bark. A plastic milk jug would work well, mulching up to the top around this jug with mulch inside as well. This is a bit of overkill but just insurance against voles or rats eating your newbie stems. Have you ever noticed any chewing damage to roses, young trees, shrubs or even bulbs in your garden? Voles love the comfy mulch home especially when it comes with stuff to eat.

Zone 6 is a very mild zone. What is the micro environment where you plan to plant them? Water well, allow to dry before watering again and stop watering when the leaves have fallen. If this is the evergreen Clematis armandii, I'd create a bit of a structure above, cover with row cloth and cover edges with soil and mulch. In fact, this would be fine to replace the milk jug altogether. No fertilizer until spring!

If they are subject to high winds, then you need to provide wooden shingles to block the wind. If this location will have lots of wind throughout the year I'd find a more sheltered micro environment more sheltered for their permanent home.

Answer 2

I agree with Srihari, generally, and also with most of what Stormy says, with a caveat. Assuming they've been outdoors all summer, plant them, now - but don't plant into a mound (sorry Stormy!). I don't know whether your Clematis are large flowered cultivars or species clematis, but cultivars can be prone to clematis wilt. The way to discourage this from killing your clematis is to prepare the planting area at least twice as deep and wide as the rootball of your plant, preferably incorporating some good compost (humus rich material such as good garden compost, composted animal manure, whatever), take your plant out of its pot, place in the hole at an angle, so its partially on its side, and low enough so that, when you backfill with soil, the bottom inch or two of stems are also buried. This encourages more shoots off the roots next year, so even if some succumb to clematis wilt, plenty more should take over. Mulching over the top should help give protection, but if you get good snow cover during winter, that will act as an insulator too.

If animals chewing at the shoots might be a problem, then incorporating some kind of collar or tube at the base might be useful, but might not - new stems will arise from the base anyway, and these may be outside any type of collar or tube you've put in place. Even if the stems do get cut by something, the clematis will produce more, as long as they're not continually cropped.

Your clematis will be safer in the ground than out of it through winter, but bear in mind when deciding where to plant, they need something to scramble up (can be a shrub nearby or clematis mesh or pea sticks or an obelisk, or a huge tree or wall, depending on variety), and they like their roots in shade and their heads in sun in a fairly sheltered position.

Without any clues as to which varieties you've grown, its impossible to advise on pruning, height and spread, etc - there are some varieties that may not survive the cold, but most will. Consider also the huge variation in size of clematis when thinking where to plant - they range from 8 feet high by 4-6 feet wide to 35 feet high and 12 feet wide, the larger ones being species clematis such as C. montana.

Answer 3

What specific species of Clematis do you have? Or do you have photos? Where exactly are you located, or do you know what your specific USDA Zone is? Identifying the plant species and variety and zone will almost always help get you very close to an accurate answer about many questions, including over-wintering.

Not all of the Clematis species will overwinter uniformly, but Clematis are hardy and will usually survive outside.

Yet, there is always the risk of a very long and hard frost spell in any winter, which means you do run the risk of them becoming damaged. If you have the space, and a way to keep them away from pets, you can bring them in, just remember to do it at the very edge of winter. When planning to keep plants alive for several seasons, it is best to try to keep them out as much as possible, and helping them put up with harsh weather.

You will also need to prepare your house/garage/shed/green house for bringing them in.

If you do keep them out, mulch them as much as possible, giving the roots the chance of retaining warmth over the winter.

I will refine the answer if I learn more about your zone, etc.