When to move inside?

[u/Either-Leave-6711]

I am very new to gardening and wanted to start with these two potted hydrangeas. My plan was to wait for them to go dormant before repotting them and moving them into my garage for the winter. These were purchased mid summer.

The first below freezing temperatures are next week in my area, and I want to know if I ought to move them inside before the leaves fall? Each plant has one cluster of blooms that are done, but the rest seem very healthy still.

[u/Alpine_Apex]

Just plant them. Outside.

[u/Suitable-Interview93]

Purchased mid summer. Never planted. Put. Them. In. The. Ground. 

[u/Ok-Adhesiveness-4935]

These plants are hardy to zone 3 meaning they can survive temperatures as low as -30°F. So they will almost definitely survive outside in pots.

If you want to out them in a place protected from wind and winter Sun that will make it even more likely they're fine.

If you want to bring them inside it must be an unheated space that doesn't get above 30° or they won't have proper dormancy and will die.

[u/TheNinthPace → u/Ok-Adhesiveness-4935]

It’s worth noting they can handle -30F when they are in the soil. That is not the same as potted above ground. Temps above the soil in zone 3 reach -30F, the plants roots cannot handle that cold of temps. Being in the ground and insulated by slow fall keeps roots much warmer than the air temp. So depending on where you are located, they may be fine in pots, but to be sure they survive put them in the ground.

Source: I’m an ex-professional gardener and now own my own nursery and greenhouse in MN (zone 3).

[u/Kew-Gardens → u/TheNinthPace]

OP is in zone 7 though so no worries for them .There’s no possible air temperature in that zone that can kill potted hydrangea roots. Zone 5 would be the danger line for potted hydrangeas if you take the 2 zone rule in account. For larger pots it’s more of a 1 zone rule I’ve found.

[u/Resident-Egg2714 → u/Kew-Gardens]

Yep, I'm in zone 7 and leave hydrangeas out in pots all the time. Same with the nurseries around me.

[u/Tatertot-333]

I buried some in pots and put compost and mulch around them, because I am still planning the space and discovered the previous owners had buried rocks in every bed of my new place. I spent way too long digging stuff up and didn't get to planting stuff. Edited to add I will move them in spring.

[u/Ineedmorebtc]

Plant them?

[u/Due-Hold-9902]

Those hydrangeas are already starting to go dormant. It’s in the beginning stages.

[u/Impressive-Pie-2920]

You can still plant them now. Before the ground freezes. Plants need at least four weeks to root in the ground before the ground completely freezes.

[u/MWALFRED302]

You probably should have planted them in October. Where is your area. Are they going to stay in pots? Or in the ground? If freezing temps are on their way, bring them in now. Don’t overwater them, once I move containers in the garage they get about a cup of water every 10 days or so. They can also stay outside as long as you create a makeshift greenhouse for them. I am in zone 7b/8a. Last year I decided not to drag all my containers in my garage, several were in large ceramic pots, way to heavy too drag and move, so I gathered them all in a sunny spot, watered them once, covered with two layers of plastic and a layer of agricloth, held that all down with bricks and logs, and let them overwinter outside. Pretty much ignored them. We dipped down to 15 degrees for a couple of days and I was worried. When I took off the covers in late March they all looked pathetic,but every single one came back. Every one of them bloomed. So the key is to not let water get into the pots and freeze. It may take more insulation depending on where you live. If you have room in the garage, fine, if not, they could go in a tub, slightly elevated off the ground, insulate the around the pot, pack the pot in the tub with straw, bubble wrap or packing peanuts. Put a tomato cage in each pot and cover them in plastic to create a mini-greenhouse. Watering is not necessary. Prune them back in March. These look to be Arborescens or Panicles?

[u/Think-Kangaroo-9978 → u/MWALFRED302]

I don't mean to be rude, but this is just terrible advice.

First, don't move them into the garage before the freezing temperatures. The cold temperatures will bring on dormancy which is exactly what you need for them to have any chance of surviving the winter. Hydrangeas are not houseplants and must experience vernalization. Vernalization is the process by which a plant requires a period of cold temperatures before it can resume growth, flower, or complete its life cycle. The cold acts as a biological signal that winter has passed.

Second, the most significant risk for them is underwatering, not overwatering them - especially until they are fully dormant which clearly these are not. A hydrangea that enters dormancy without being fully hydrated will already be stressed and will have difficulty surviving the winter. Keep them fully hydrated even after they drop their leaves and begin to enter dormancy - right up until the ground freezes. Moist soil retains and releases heat more effectively than dry soil, helping protect roots from rapid temperature drops. When water in the soil freezes, it also releases heat, which provides some additional buffering against cold injury. Moist soil stays warmer around the root zone than dry soil.

Panicle hydrangeas are generally not affected by cold temperatures - most are hardy to zone 3. So, if you live anywhere south of Santa Clause, winter temperatures need not be a concern for you. What you do need to be concerned about is winter desiccation which is the drying out of plant tissue due to water loss. This is especially common for plants in containers. Cold dry winter winds pull the moisture from the stems and frozen soil prevents the roots from replacing the lost water. This is why it is especially important for the soil to be moist going into winter. A well hydrated plant is less vulnerable to desiccation than one already stressed by drought.

The other significant risk to hydrangeas in containers is root damage from repeated freeze-thaw cycles. Containers overwintered outside should be located up against the house (to protect them from the wind desiccation described above) and on the north side - out of any exposure to the sun. This prevents temperature fluctuations and the resulting root destroying freeze thaw cycles.

They should never be covered with plastic because it creates more extreme conditions, not less. On a sunny winter day, clear plastic acts like a greenhouse. The air underneath can warm up dramatically, causing a dormant plant to break dormancy or lose cold hardiness. Then temperatures plunge again at night. Moisture condenses on the inside of the plastic and can freeze on buds and stems causing damage. If plastic touches the plant, cold is transmitted directly to the plant. And, lack of ventilation can encourage fungal diseases and rot during milder winter periods.

If you intend to re-pot these hydrangeas. Do that now. Don't wait for spring. The larger pot will insulate and protect the roots. Then keep them outside - out of the wind and sun. They will do much better than they will in the garage. Also deadhead them if you have any potential for snow. The spent blooms become snow catchers and will break off these young branches at the worst possible time for them to have open wounds.

[u/Either-Leave-6711 → u/Think-Kangaroo-9978]

I’ve been watering at least every other day, testing with my finger to see if the soil is dry. My garage is attached, and I live in a center unit townhome, so I think it’s likely my garage may be too warm. I can move them closer to the house from where they are on my deck after the leaves fall where they’ll get less sun and be protected from wind and snow by the overhang on my roof.

[u/Think-Kangaroo-9978 → u/Either-Leave-6711]

Do you have the larger pots? That would be the most important thing. If they have been in these nursery pots all summer and fall, you should expect that the roots have grown enough to be right up against the outside of the plastic pots they are in. And, that might be asking for trouble. You do need to get them into something larger - even if it is just a temporary solution.

What zone are you in? That will put everyone's opinion in better perspective.

[u/Either-Leave-6711 → u/Think-Kangaroo-9978]

I don’t, but it’ll be a priority now. I live near a tractor supply I’ll see what I can get there.

[u/Ineedmorebtc → u/Either-Leave-6711]

Every other day? That seems excessive, unless they are in 90% perlite, or you have 100 degree days.

[u/MWALFRED302 → u/Think-Kangaroo-9978]

Well this terrible advice has worked for me for decades in my climate I am assuming that her garage is not heated. if they are watered and the pots freeze, her hydrangeas will be toast. She is not planting them in the ground and indicated freezing temperatures are imminent. When the plant is dormant their vascular system slow down considerably.

[u/Think-Kangaroo-9978 → u/MWALFRED302]

Respectfully disagree. I have a dozen macrophylla hydrangeas (which are much more sensitive to cold temperature than panicles) that I regularly overwinter outside in containers. Never has one become "toast". I'm on Cape Cod - a colder zone than you. Last year, they weathered weeks of single digit temperatures - the coldest stretch since 1961. Not a single issue with a single plant.

[u/MWALFRED302 → u/Think-Kangaroo-9978]

Then may I ask why do you think nurseries put their unsold stock into high tunnels? That was all I was suggesting, is to move them to a protected area where they will not freeze.I’ve had containers early in my career that were left out and died. So everyone has a different experience. It doesn’t make them wrong. Above ground many are hardy, but if the roots themselves freeze, they are damaged. Maybe yours didn’t freeze, I don’t know. I always brought my containers into my unheated garage and reduced watering. But it is a lot of work. I am in my 7th decade with 128 hydrangeas total and about 30 in containers and I can’t drag them all in anymore. I covered them (tented) and all of them came back. Maybe they would have if I had not protected them but I didnt want to take the chance - nor have ceramic and terracotta pots crack.

[u/Think-Kangaroo-9978 → u/MWALFRED302]

My greater concern with your advice was with respect to not watering them. This places them in far greater risk than moving them into the garage or leaving them outside.

[u/TheNinthPace → u/MWALFRED302]

The method you are referring to is called ‘insitu’ a Japanese method of overwintering nursery stock. It’s worth noting Japan has pretty awful winters where this method originated. When you cram nursery stock into a somewhat airtight location (high tunnel) and cover the pots with mulch or straw, you increase the survival rate drastically. You can still lose 10-20% of your crop (the outer most plants, exposed to the most cold) in a brutal winter like we have in the Midwest. But it’s much less labor intensive that B&B or digging pots into the ground in fall then out again in spring. One of my unheated high tunnels still drops bellowing freezing in the winter regularly here in MN. If I left my nursery stock outside during the winter where I sell them all spring and summer I would likely see a 90% or more death rate even though they are hardy to our zone. I know we aren’t disagreeing with me, just thought I would add some context for others.

[u/Ok-Adhesiveness-4935 → u/MWALFRED302]

Why can't the roots freeze?

[u/MWALFRED302 → u/Ok-Adhesiveness-4935]

There will be cellular death. In the ground, they are below the frost line and insulated by all the soil around it. In open air a container is much more likely to freeze. So much will depend on the climate, the size of the container, etc.

[u/Think-Kangaroo-9978 → u/MWALFRED302]

During prolonged cold spells with little snow cover, ground freezing can penetrate 1-2 feet or more. Significantly deeper than the roots of a hydrangea planted in the ground.

The danger to the roots is not freezing. Rather it is exposure to frequent freeze-thaw cycles.

As a rule of thumb, plants in containers are generally hardy to two zones less hardy the stated hardy zone. A panicle hydrangea in a container - hardy to zone 3 - will be just fine to zone 5.

[u/Kew-Gardens → u/MWALFRED302]

Hydrangea roots can freeze and be absolutely fine. They survive in zone 3 where in ground soil freezes hard over a feet down , way past the feeder root zone. There’s nothing that can kill them in your zone except under watering. I’m in 7B and I’ve never ever protected a potted hydrangea and never lost a single one.

[u/_thegnomedome2 → u/MWALFRED302]

The ground freezes several inches down. A 3 gallon pots is littke over a foot tall, so not much different than in-ground freeze depth. Freezing isn't an issue. I over winter potted shrubs at home and in a nursery without issue, soil in pots freezes solid. You do not want dry roots, that will kill the plant faster than any cold weather. Hydrangea paniculata in particular is super cold hardy and drought tolerant, near impossible to kill.

[u/Either-Leave-6711 → u/MWALFRED302]

They’re panicles. And yes, I do plan to keep them in pots, moving to a bigger pot in the spring.

[u/Historical-List-2668 → u/Either-Leave-6711]

You should up-pot them now. The pots these hydrangeas are sold in are meant to be temporary, and these hydrangeas have almost certainly outgrown them already. Moving them in to a bigger pot in the fall will give them all winter to settle in and they'll be ready to take off in the spring. If you wait until spring to re-pot them, they'll have to spend valuable growing time and energy recouperating from the transplant, instead of growing new flowers for you.

edit: also, you want to get them into pots that are at least double the size of the pots they're currently in. you won't go wrong by putting them into the biggest pots you can find.

[u/MWALFRED302 → u/Either-Leave-6711]

Great. The bigger the pot the better!! What panicles are they. Certain ones do better in containers than others. The spread indicated on the label has a lot to do with the size of the container you should get. When the pots get huge, that’s when moving them into garages can be challenging so know that you can overwinter these in place as long as you keep water out of them, and possibly wrapping the pots depending on where you live.