Hi everyone! I am gardening for the first time and have several plants in fabric grow bags. The temperatures in my area are dropping below 32F at night but still getting all the way up to 60F during the day. I have several types of blueberries, strawberries, raspberries, a salmonberry, and a fig tree in grow bags. Some have fall foliage and some are still green, and the strawberries are actually still putting out new growth. I’ve read that it’s bad to leave containers out in freezing temperatures due to root damage regardless of how hardy the plants actually are. I’ve placed them in my garage, but unfortunately, I think that the garage is heated and closing the vent to the garage does not seem to help much. I have a few questions which are:
When should I permanently keep the plants in the garage? Right now I am moving them outside during the day and inside at night.
Do I need to wait for them to go through their fall foliage and drop their leaves? Will it damage the plant to put it away for the winter while it’s still fully leafed out?
Is there any way to keep the garage from consistently staying heated, such as leaving the door cracked? Otherwise the plants will “overwinter” in a 67F environment which I have read is not an ideal temperature.
A good rule of thumb for starting is about two temperature zones displacement between pots and ground. So a plant hardy to zone 3 in ground has good potential for zone 5 in an appropriately sized pot.
If you can shelter from wind and frost, especially while the plant is not yet dormant, you’ll prevent a lot of mishap.
If your garage is fixed to the single temperature in your house, there may be reasons why. Before adding the cost of heating the outdoors by leaving a door/window cracked, make sure you are not risking things like water lines. You could likely build a small lean-to type shelter on the side of the house somewhere you could either let passive heat escape keep at an appropriate temperature or heat with a small portable heater to something above freezing.
That’s far from complete, and not a direct answer, but it will hopefully broaden your starting point a bit.
Not to hijack your thread, but I have a similar question. I have some plants (blueberry in a roughly 25gallon pot and several wild plum suckers in 1 gallon pots) that I have moved into an unheated shed. In the dead of winter, when it is in the single digits, it will get below freezing in there. Last winter I had 3 blackberry bushes that I had in 5 gallon buckets that I over wintered in there. I know that at some point the soil was frozen solid, but this spring they still came back to life and continued to grow. Just wondering if there is any extra things I can do to help with the survival of the younger plants?
Not true.
Potted figs need some protection when temps drop into low 20s.
My potted blueberries, apples, pears and peaches have been fine when temperatures dropped to 0F. I’m not sure about lower temperatures.
Pilling leaves or straw over them can add some protection.
Very small seedlings or rooted cuttings might some additional protection.
Thank you for the information! These are all cold-hardy to well past my zone (6b) but I worry that it won’t matter if the soil freezes and kills the roots. Also thank you for the info on the garage. I know the water heater is actually in the garage and generates a lot of heat by just being there, but I’m not sure about all the piping. I do have access to the crawlspace, which would be cooler and darker–would that be a good place to put things? It has had moisture control treatment recently so hopefully it wouldn’t be too wet in there.
Do you wrap the containers at all with anything? My concern is that since they are in fabric grow bags, they will be very exposed to the cold temperatures from the sides.
Northern blueberries… I’ve had a potted one for a decade (fabric pot) and it sits outside every year in subzero temps without any damage. I do try to move all of my outside pots against the house in a protected area and if I’m really motivated I put some bags of mulch against the pot. However, I can’t say I’ve done this every year consistently. I’ve also left blackberries in plastic pots sitting on an asphalt driveway exposed and they were fine. Temps anywhere from -4°F to -11°F or cooler, the blueberry lived with me in 5b at one point.
The figs can be a little tougher because they tend to be damaged due to waking up during warming temps in a garage followed by a cold snap. I don’t have great advice there because I’m still learning how to shuffle mine in and out of the garage and basement to keep them happy.
Thanks for the info! I’ve heard a lot of people say they just leave their blueberries out. I would like to do that but my area regularly has cold winters where the days averages in the 10-20s, going as far down as single digits. How do I know if it will be safe for them or if they will die in the freezing temperatures? Also, for plants that do need to be brought in, what do I do for the ones that are still fully leafed out and green? My garage is about 57F on average lately with the heating vent closed so I’m worried that won’t be cold enough to induce dormancy. Our weather is swinging to above freezing during the day and below freezing at night right now.
Put them just right outside the garage. I left an Elliot outside in Colorado Springs and it survived last year to this.
Scenario 2: leave them in your heated garage until about January/ February or even March. They only need about a months worth of coldness to bloom again.
I don’t think they all need dormancy but more so a period of temperatures under 45 to bloom next season
I read somewhere there is a rule of thumb. You subtract one zone for plants in pots. So if a plant is rated for zone 9 in the ground, it will only be safe to keep outside in a container in zone 10 or higher. A plant rated for in the ground in zone 8 will only be safe in a container in zone 9. I don’t know if this is 100% true, but I have read it from several sources.
I wonder if those experiments state what type of pot or area the plants were grown in because i would think it’s the opposite if they’re in big black nursery pots. But if terracotta, yes? Nursery pots seem to hold heat a little better vs terracotta or white thin pots. Also the area they’re in too. Closer to the house or a heat element = better survival for potted plants vs out in the open
Doesn’t matter how much heat a pot holds, it’s far less than the earth. Here the soil never freezes so with marginal stuff that I can’t move to the greenhouse I’m far better off planting. I think @jsteph00921 is about exactly right with the subtract a zone, but it could be 2. Granted I do not really think this applies to super cold hardy plants which can grow where the ground freezes 6+ inches deep.
It’s strange because I’ve had the opposite experience when i was in Colorado and the ground would freeze down far enough to bust sprinkler systems. My raspberries survived in my 25 gallon grow bags but in ground did not. However my grow bags were right next to my house and they didn’t freeze except the top few inches and around the sides a little. Maybe there was something else that was messing with my plants in ground, who knows. So this is what I’m basing my comment off of but ya’ll could be right. I haven’t looked much into it overall
I’ve never really found a good reference on critical temperatures for potted plants, but I think the two-zone rule mentioned above is a good rule-of-thumb.
For reference, I left some Z4 rated blueberries out in 7-gallon pots last winter and they were fine. It was abnormally mild here last winter for z5A (it hit -10 to -15’F for consecutive nights but we had 12" snow cover). I’m not sure the soil temp in the pots, but it was presumably well below freezing (maybe 10’F if I had to guess?).
For everything but the fig – another option that probably provides more like 1 zone of protection is to make an ad-hoc raised bed with some random scrap wood, set the pots in it, and fill in the gaps with mulch (or packed sawdust, or packed chopped leaves, etc.). I’d also cover the strawberries in a few inches of straw, leaves, sawdust, etc. to protect the crowns from wind/cold.
A house is a massive heat sink. I have a concrete paver patio with full south exposure that fits within an L shape formed by two buildings. The area creates a microclimate that stays 5-8 degrees warmer than anywhere else on the property. That’s where I planted my citrus in the ground and it does very well. We get frost on average 20 nights a year, yet it only frosts in the microclimate a few nights each winter.
Also raspberries are super hardy, capable of enduring temps down to -20 F. That is plenty cold to freeze the earth to a depth of 3 feet. Since raspberry roots are very shallow, within the first 18-24” of soil, they are capable of being frozen solid and still bouncing back.
A northern blueberry with good roots isn’t bothered by temps below freezing. Mine have been fine in -11°F and possibly lower. If you mulch them in against a wall they’ll definitely be fine.
Your plants might be completely fine and you can save yourself some work every year.
For what it’s worth, I have a ton of different varieties of blueberries in grow bags, from 7-gal to 20-gal and they all survived my last winter in Chicago. I don’t even have them near my house and they get a lot of wind. They’re mostly rated for Z5, some Z4, and I’m located in an area that is Z6a and was very recently Z5b.
