每日吃瓜

Good Morning

I am a beginner and I have purchased four small bonsai:

Chinese Elm
Japanese Acer
Pyracantha
Brush Cherry

Can someone please advise if the trees are ok to leave out at night with temperatures down to 4 degrees at night?
I have been placing them in a cold greenhouse to be cautious but an expert's advice would be welcome, thanks.

Chinese elm and Acer is perfectly fine.

I do not have first hand experience with the other two, but I would guess a night at 4c would be no problem.

It is not that cold! Nothing to worry about

Thanks for your reply which is much appreciated.

At what temperature should the trees be placed in a cold greenhouse for protection?

My mature chinese elm is kept protected in the greenhouse from early winter. Around the time we have subzero temperatures 24h. In mid winter the lovest temperature it has endured inside the greenhouse is -18 night and -10 in the day. The whole cold spell lasted for 6 weeks. Not that cold all the time, but always below 0. In UK, I would asume that the temperature is not a problem and greenhouse not necessary. However overhead protection from excess rain in winter may be needed.

My acers is kept outdoors all year. Same temperatures as in the greenhouse in the nights, but slightly colder in the days when the scarce sunlight actually heats the greenhouse a little bit. Acers is not that sensitive to excess water and would be perfectly fine outdoors at all time in UK i suppose.

AJames99 wrote:

Thanks for your reply which is much appreciated.

At what temperature should the trees be placed in a cold greenhouse for protection?

It really depends on the species. Around here it never gets cold enough for larches, which worthy outdoors all year long all the way to Canada, but southern pines would need some protection at 20F/-7C, maybe Virginia. You can get a strong hint of this from the fact that Southern pine is different from Virginia pines and they don't have much common territory.

I checked all your trees hardiness zones online. You can do it yourself by googling species + hardiness. 每日吃瓜 in pots are slightly more sensitive. I tend to make it a rule to add one zone to the lower value. FEX pyracantha coccinea is 6-9 in ground. That makes a good rule of thumb that it is 7-9 in a bonsai pot. 7 is down to 17,8 degrees which would make it most likelly ok to keep outdoors at all times in UK.

As mentioned before how wet it is makes a difference for some species and the duration of the cold spell as well. USDA zones is a good guideline, but not a guarantee.

The point I was making is that it is not cold. We have had lows above freezing so there is no need for anything to be protected. The problems come when in May we get frost. That is far more damaging than in the winter. I am hoping we don't have any frosts in May but we have for the last three years at least.

I think how fast temperatures change is important. The tree in the ground gas its roots stuck in a massive heat sink. In a pot on a stand the roots change temperature very quickly.

Adding one to the zone us a good guideline.