As gardening evolves, so do its practices. As of lately, perennials seem to have come out of their “in-ground planting only” box and are now being potted along with their annual and biennial counterparts. These plants are being heavily favored by gardeners due to their durability and compact size; however, is it really possible to keep potted perennials safe and healthy throughout winter?
You can keep perennials in pots over the winter as long as you follow a thorough maintenance schedule. However, never overwinter potted perennials in a warm space (such as indoors or in a greenhouse), as the plants won’t be able to enter dormancy.
In the rest of this article, I’ll delve further into the best practices for overwintering your perennials in pots. Therefore, keep reading to learn more about some of the best tips and tricks to keep your potted perennials healthy and thriving even during colder months, along with some additional information on the best-suited varieties for the process.
How To Keep Perennials in Pots Over Winter
Even though, as many gardeners can attest, keeping perennials in pots over winter is entirely possible, there’s a lot of planning and hard work that goes into the process. Perennials are meant to last for several years to come, which means that learning how to keep them thriving even under harsh weather conditions is an invaluable skill.
Hardy perennials are usually the easiest variety to overwinter successfully. For example, hostas are among the most popular perennials gardeners like to keep potted throughout colder months (if you’re interested in learning more about overwintering hostas, I highly recommend checking out this article).
These types of perennials need to go through a dormancy phase, which lasts all throughout winter and ends in spring. Therefore, in order for the process to be successful, you’ll want to make sure that the external conditions allow for the plants to safely enter this phase. This means that you should never keep your potted perennials indoors or in another similarly warm space.
If you do, they won’t be able to go through dormancy, and as a result, they likely won’t have the necessary energy and nutrients to bloom, grow, and reproduce once spring comes.
On the other hand, keeping your perennials in an excessively cold climate also has its risks. Potted perennials are especially susceptible to root damage caused by freezing temperatures and high levels of rainfall.
Therefore, finding a perennial that agrees with your location’s climate is always essential. To learn more about which plants can be successfully overwintered in your area, check out the USDA Plant Hardiness Zone Map.
When growing a perennial in-ground, the soil provides an extra layer of protection and insulation from the elements. However, pots aren’t as effective when it comes to keeping your plants protected from the elements; therefore, you’ll want to be extra careful when determining whether a perennial has a realistic chance when it comes to being overwintered in your location.
Moreover, temperature fluctuations are much more significant above ground than they are below it. As a result, potted plants are often subjected to a continuous freeze-thaw cycle that can often end up rotting their roots.
As a rule of thumb, if you’re thinking of keeping your perennial completely outside (uncovered and unprotected in any way) all throughout winter, you’ll want to choose a variety that’s at least one or two zones hardier than your location. For example, if you live in Zone 7, you’ll want to aim for a plant that’s hardy to Zone 6 or lower.
Tips for Keeping Perennials in Pots Over the Winter
Here are a few additional tips and tricks on keeping perennials in pots over the winter:
- Leave large pots outside. Large-sized pots can be left outside with little to no issues (assuming you’ve followed the hardiness zone rule mentioned earlier). The excessive amounts of soil in these containers act as an insulator and make temperature fluctuations less likely to reach the perennial’s roots.
- Leave small pots in a semi-covered or protected area. While taking your potted perennials inside, as mentioned, is a no-no, you can still provide some protection without risking the plant forgoing dormancy. Perennials that are potted in smaller containers are more sensitive to temperature and humidity fluctuations; therefore, you’ll want to keep them in a shed, unheated garage, or porch to increase their chances of survival.
- Try to keep potted perennials at ground level. Even though keeping a small-potted perennial on a semi-sheltered porch is still better than leaving it outside, it’s best to avoid overwintering your plants in raised structures. Instead, always try to keep them at ground level to ensure they’re as undisturbed by the elements as possible.
- Try to keep sheltered pots facing north. Depending on your home’s layout, sheltering your perennials near a structure that allows them to face north isn’t always possible. However, always follow this rule of thumb if you can, as by doing so, you’ll keep your plants away from the wind and sun (exposure to which could make it harder for the perennials to enter dormancy).
- If all else fails, bury the pots. Suppose you have a prized perennial that you can’t risk exposing to the elements or one potted in an especially small container. In that case, it’s best to bundle it with other potted perennials and bury them throughout winter to better insulate the roots. Make sure to cover the plants with at least 5 cm (2 in) of mulch. However, take out the pots to let the leaves unfold when the weather warms up.
- Try to group several potted perennials together. Potted perennials that are bundled together have a much better chance of survival. That way, the pots will act as a buffer between the roots and the excessive temperature and humidity fluctuations, keeping your perennials safe throughout winter.
- Don’t overwater perennials. As soon as these plants enter dormancy, you won’t have to water them at all. Even before that, a generous once-a-month watering should suffice. If you’re getting enough rainfall, you might even want to scale the watering frequency back even further. Overwatering your perennials increases the risk of root rot and makes them less prepared to enter their winter sleep.
- Never fertilize perennials during winter. Fertilizing your plants during this time could mess with their natural dormancy cycle. Instead, wait until active growth begins (during spring) to nourish your perennials.
- Gradually re-introduce perennials to their normal growing conditions in spring. As the temperatures rise, slowly re-introduce your perennials to the elements and their regular watering routine. However, make sure to go through this transitional period one step at a time, as you don’t want to overwhelm your plants.
- Choose the right pot. The right pot design and material can significantly affect a perennial’s chance of survival. For example, porcelain or clay containers are prone to breaking in winter, which means that using them requires taking an unnecessary added risk. Therefore, you’ll want to opt for a metal, plastic, or wood variety instead.
Perennials You Can Keep in Pots Over the Winter
As mentioned, the only surefire way to find out the best species to overwinter in pots in your location is to study the Plant Hardiness Zone Map. However, even as it stands, there are some perennials that are better suited to be potted and, therefore, can handle freezing winter temperatures much better in such a set-up.
In this section, I’ll be listing some of the best perennials you can keep in pots over the winter; however, keep in mind that their suitability might vary depending on your location.
- Brunnera macrophylla
- Dianthus (Pinks)
- Tiarella (Foamflower)
- Echinacea (Coneflower)
- Achillea (Yarrow)
- Salvia (Perennial Salvia)
- Houttuynia (Chameleon Plant)
- Myosotis (Forget-Me-Not)
- Phlox subulata (Creeping Phlox)
- Iris ensata (Japanese Iris)
- Thymus (Creeping Thyme)
- Polemonium (Jacob’s Ladder)
- Sedum (Stonecrop)
- Heucherella (Foamy Bells)
These are just a few perennial varieties that, with enough care and maintenance, can thrive when potted. However, they’re far from the only species that you could add to your gardening collection. Therefore, I highly suggest reading through this comprehensive list before making a decision.
Contrary to traditional gardening beliefs, perennials can be kept in pots over the winter. However, the process takes quite a bit of planning, time, and effort, so make sure to read through the tips and tricks mentioned in this article before taking on such a challenge.