Is it ok to leave the lids open on my coldframe/small greenhouse

Hi all

I'm fairly new to gardening so unsure of many things still and mainly garden through trial and error!

I have a couple of smallish cold frames/greenhouses that I use to keep my new plants in at this time of year when they arrive from online stores (such as J Parkers/Suttons seeds etc). I use them as a holding place until the weather warms up enough to plant them into hanging baskets and pots on the patio.

This years plants are:
Ageratum Ariella Mixed
Anagallis Skylover
Lobelia Regatta Mix (Maxi Plugs)
Trailing Surfinia Mixed
Cosmos Apollo Lovesong (Garden Ready)

I am still waiting for the cosmos to arrive but the others are all here and I have potted them on to slightly larger pots and put them in the frames.

The frames they are sitting in are simple wooden/plexiglass frames with doors at the bottom and 2 lids that raise up and can either be left open or closed down. My question is can I leave the lids open all the time at this time of year or do I need to close them when frost is likely? I am unsure if the plants I receive are hardy enough to tolerate the cooler nights or not. If should be closing them in cooler weather, how cold does it need to be to shut them?

They are sitting in the alleyway at the side of the house and don't really get much sunlight but there is nowhere else to put them until they are ready for transplanting into their respective containers.

I live in West midlands area.

Any help would be greatly appreciated.

Thank in advance

Lady F.

 

Hi Lady Fanny, welcome to the forum. I'm in the West Midlands too, I've had my cold frames left open for a few weeks now, the only reason I would close it now would be if there was a frost forecast, if you could find a spot with some sunlight it would be beneficial to the growth of you plants. Hope this helps.

 

I open my cold frames in the morning and close them at night but I don't know if it makes a lot of difference as there is never a great variance between the low outside and the low in the frame, according to my thermometer.

 

Really the idea of a cold frame this time of the year is a half way house between a heated green house and totally exposed.
I've not left mine open at night yet, I usually wait until night temperatures are 10c or above but I do prop the lids up a bit.
Basically you adjust things according to the weather, so leave open on mild nights but close down on cold nights.
I also drop the tops down when it's raining, being soaking wet in there attracts too many slugs for my liking.

 

You want to keep an eye on the weather forecasts, as you can see from this free one, its likey to be unusually quiet cold around early May, so you need your cold frames closed at night and even the part of the daytime to avoid you plants being 'checked' or even damaged by frost or snow.

 

I checked my digital thermometers this morning and the outside minimum overnight temperature recorded 5.2°C and the cold frame registered 5.8°C.

 

There is a bit more to it than purely temperature otherwise ,why bother with having one.

 

A cold frame keeps the rain off tender plants as well as stops wind damage (unless your frame blows away). However, I have read that a cold frame keeps the temperature in the frame 5°C to 10°C warmer than outside. I have only ever seen that in full sunshine but next to nothing overnight.

 

Mine have been left open since Thursday. Everything seems to be fine. I'm in Norfolk

 

Thanks for all your replies. It's pretty much what I've been doing anyway but I've never been sure how hardy the plants I've ordered really are and how much protection I should be giving them.
I generally plant them out into their final pots in May after I'm sure the night frosts have gone. Sadly we only have a small garden and there's no room to put the frames anywhere else as they're quite big. It's not ideal and I'm sure the plants would grow better and bloom faster if they were in more sunlight but I can only work with what I've got. They get a small sniff of sun first thing in the early morning as the sun moves round but that's all.
Once planted out, the containers are usually in full bloom by mid July.