Blueberry plants grown in containers will thrive in the Summer but they will usually need a little extra care in winter to prevent their roots from freezing. Find out how to protect a potted blueberry bush in winter, whether you’re overwintering it indoors or outdoors!
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Determining Whether to Overwinter Outdoors or Indoors
Hardiness varies between different types of blueberry shrubs. If you’d like to overwinter yours, the first step is to find out the lowest winter temperature that it can withstand outdoors. Based on this, you can decide whether it can stay outside in your climate or if it’ll be better off in a shed or garage.
When it comes to protecting a blueberry plant grown in a pot in winter, it’s important to remember that they’re not as hardy as blueberry plants grown in the ground surrounded by plenty of soil. Their roots just aren’t as well-protected in a container.
As such, it’s best to take the USDA hardiness zone your plant is rated for and then add a 1-2 zones if you want to overwinter it “outdoors” in a pot.
For example if your blueberry plant is listed as hardy to zone 4, that means it will survive “in the ground” to typical temperatures of zone 4.
If it is in a pot, it will only survive outdoors to zone 5 or 6 however. In other words you may have to bring it inside if it is in a pot.
The maximum most of the blueberry cultivars can handle in terms of cold weather is Zone 3. Although your mileage may vary depending on the cultivar, there are five basic “categories” of blueberries:
- Lowbush: minimum Zone 3 (so Zone 5 in a pot); a few varieties down to Zone 2.
- Half-high: minimum Zone 3 (so Zone 5 in a pot).
- Northern highbush: minimum Zone 4 (so Zone 6 in a pot); a few varieties down to Zone 3.
- Southern highbush: minimum Zone 6 (so Zone 8 in a pot); a few varieties down to Zone 5.
- Rabbiteye: minimum Zone 7 (so Zone 9 in a pot).
Based on this hardiness information, you can decide whether to overwinter your potted blueberry shrubs indoors or outdoors. If you’re in a zone that’s too cold for the hardiness designation of your plant, you’ll have to find it a sheltered spot until things warm back up.
Know also that blueberries need a dormancy period. This means you can’t keep them in a warm place like your living room during winter.
In fact, if you live in a warm climate like Florida, this can actually mean it’s difficult to grow varieties but southern highbushes and rabbiteyes. The others just need more cold to grow properly!
Protecting Plants: Overwintering Outdoors
Unless you live at least two zones above the hardiness cutoff for your blueberry bush, it’s important to take some steps to help protect it is you are going to leave it outsid over the Winter.
The roots are the main consideration (as the leaves and tips will grow back), and the roots are more exposed to the cold in a pot. The more insulation you can add to help keep them warm, the better.
The shallow blueberry root system can really suffer and even die off if it ends up freezing, so it’s important to prevent this from happening. This especially applies if the plant is in the type of a container that doesn’t offer much in the way of protection (i.e., thin plastic)
Something like a small, single-walled thin plastic pot exposes the roots way more than an extra-large and thick container made of fiberglass.
**Pro tip: If you find temperatures are rising and dropping sporadically, like when spring is right around the corner, you may need to go ahead and place the shrub in a garage or shed. They can suffer if they don’t go fully dormant (or emerge from dormancy) due to warm temps and are then hit by sudden cold. The same applies if your area is receiving unusually cold temps this year.
Here are some steps you can consider to help your potted blueberry bush survive being outdoors in winter:
Bury the Container and Roots
The best thing you can do for a blueberry shrub when overwintering outdoors in a pot is to bury the container in soil. If you have a garden with some space available, this will really help protect the roots.
Just dig a hole that matches the container, pop the plant in there and cover in such a way that the roots can benefit from the extra insulation but the stem is exposed. If you think more protection is needed, you can also add some extra mulch and/or cover as described below.
If you can’t bury the pot, try to at least place it in a sheltered position. A spot against a wall or other protected area will help protect it from the worst of the winter weather. If you have multiple potted plants, you can place them together with the most sensitive ones in the center.
As you’ve probably concluded by now, overwintering blueberries in a pot outdoors is all about insulation. Mulching is a great way to do this: you can add up to 8″ of straw, pine needles or leaf mulch in and around the container to help your plant out.
There are loads of different handy pot covers and even mini greenhouses for sale that you can use to help protect your blueberry shrub. Even just a layer of plastic, bubble wrap, burlap or horticultural fleece can be helpful!
During the winter months, your blueberry bush won’t require nearly as much water as in summer. Dormant plants barely need any water, although you shouldn’t let the soil get bone dry either.
A layer of snow should be fine to keep your plant hydrated. If there is none and if it hasn’t rained in a while, it’s a good idea to lightly water once a month. No fertilizer, please!
**Pro Tip: Because they go dormant, blueberry shrubs can look quite dead during winter and early Spring, with completely brown branches and no green in sight. Even if you’re sure yours has kicked the bucket, wait well into spring to throw it out. It may just surprise you.
Overwintering Blueberry Plants Indoors
If you live in a colder zone than your blueberry shrub will be able to handle over the Winter, it’s best to just place it indoors. Sure, some really are quite hardy, but it would be a shame to lose yours!
The best time to move them indoors is late Fall, when the temperature has dropped and their leaves are no longer green (most varieties have leaves that turn dark red or maroon).
Finding the Right Location
As mentioned above, you can’t just put a blueberry plant in your living room for the winter. They need a dormancy period in order to bud and flower properly next year, To trigger and maintain this dormancy, they need to be exposed to lower temperatures.
Room temp may be perfect for us, but they’re just too warm for your blueberry! Research has found that even rabbiteyes, the least cold-hardy variety, generlaly need 500+ chill hours to bud properly the next year. A chill hour is defined as an hour during which the temperature is below 45 °F.
As such, if you want to keep a blueberry indoors for winter, it needs to be in an unheated spot so it can start accumulating those chill hours.
A garden shed or garage is perfect, as it offers protection against the wind and harsh weather conditions, but still gets cool enough for the shrub to go fully dormant. I overwinter my potted plants in my garden shed which has windows and stays around 55 degrees F most of the Winter.
Light & Water
One issue many gardeners run into when it comes to overwintering potted blueberries indoors is the lack of light. Most sheds and garages don’t have much in the way of windows.
Although a dormant blueberry bush should be able to survive without much light for a while, as it’s not photosynthesizing as much as it would in summer, it can’t survive like this for months on end. Place yours next to a window or consider using a grow light to help it pull through.
As for water, your plant will likely need more water than if you kept it outdoors. Check the soil weekly; if you stick a finger into it and it feels dry down to one inch, give the shrub a drink. Don’t overdo it, though!
**Pro Tip: Winter, when it’s dormant, is the perfect time to prune a blueberry plant. You can remove excess small branches, as well as any that are dead or don’t look their best. It really helps with getting the best possible harvest next year! You can also repot your shrub during this time.
Bringing Overwintered Plants Back Outside in Spring
If your blueberry bush has just spent a few months in a nice sheltered shed, it’s best not to move it straight back outside once Spring rolls around. After all, it’s probably not used to outdoor weather conditions (wind, hard rain) anymore, nor will it be able to handle sudden large amounts of sun.
First off, if your blueberry bush hasn’t been exposed to frost at all indoors, you shouldn’t move it back out until any risk of it has passed.
Additionally, to avoid shocking the plant, stretch the transition from indoors to outside over at least a week or two. Place it outside for a few of the warmest hours of the day at first, and be sure to pick a more sheltered spot in the beginning.