A question about frost.

[Crosbie]

Hi...

Daft question, I know...but if I use plastic bottles as cloches for my
baby lettuces will the frost get in through the hole in the bottle?

I'm trying to understand all this frost stuff.

Regards
Crosbie

[hawthorns]

they only give limited protection. if it gets really cold the lettuce will suffer

[Snadger]

Interesting things frosts! Last year I had plants at ground level in the greenhouse which got frosted yet the same type of plants on the staging survived ok.

This year I have tomato and chilli plants in the greenhouse, set at a high level with a tiny paraffin heatter underneath. The night time temp has been down to freezing point but the plants seem ok?

I think the temperature must have to drop a couple of degrees below freezing to cause permanent damage. Unfortunately some of my plants desperately need potting on and this will mean the small heater will not be enough to keep the frost off a bigger area.

Anyway.........I digress.......if you're worried about the hole in the top of the bottles either replace the screw cap or stick a bit of cling film over it!

Good luck with the lettuce!

[ClayGarden]

if your worried cork it

[Crosbie]

they'd be okay without air?

[ClayGarden]

sorry it was a joke (well partially anyway). they'd get air though roots anyway right?

[Alice]

Hi Snadger, frost is an interesting thing, and this might help.
Cold air sinks, so the lower the spot the colder it will be.
So, you might have frost at ground level, but on your staging it might be 4 degrees.
Weather forecasts give temperatures at about a yard off the ground which is why you can have a ground frost when the temperature is given as 3 or 4 degrees.
you can check this out for yourself by putting out a couple of max - min thermometers at different heights.
With tender plants, the higher you can put them the safer they will be.
Hope this makes sense to you.

[crichmond]

I planted out some broad beans a couple of month back and put a tunnel cloche over them but there wasnt enough space so I have this perpect thing that is shaped abit like a cloche so I put it over the rest we had lots of frost gorund totally white and they still wernt affected even though it had totally open ends on it.

[Snadger]

Hi Snadger, frost is an interesting thing, and this might help.
Cold air sinks, so the lower the spot the colder it will be.
So, you might have frost at ground level, but on your staging it might be 4 degrees.
Weather forecasts give temperatures at about a yard off the ground which is why you can have a ground frost when the temperature is given as 3 or 4 degrees.
you can check this out for yourself by putting out a couple of max - min thermometers at different heights.
With tender plants, the higher you can put them the safer they will be.
Hope this makes sense to you.

Hi Alice, I've worked out that it gets warmer the higher I put things in the greenhouse on the basic principal 'hot air rises'. Didn't realise about the yard high thing tho! Wondered why we've recently had ground frosts when the weathermen didn't predict low enough temps!

[Flummery]

I planted out some broad beans a couple of month back and put a tunnel cloche over them but there wasnt enough space so I have this perpect thing that is shaped abit like a cloche so I put it over the rest we had lots of frost gorund totally white and they still wernt affected even though it had totally open ends on it.

Many varieties of broad bean are not susceptible to frosts. My first sowing of The Sutton was in November. They have been through frost, snow and hail, all unprotected. Broadies are usually tougher than you think.

[Cutecumber]

I've had lettuces survive frosts even though they are not really supposed to be hardy - my Little Gem survived through the first frosts of last autumn and are faring well so far this spring. They are not, however, tiny seedlings but "young plants" that have been pot raised, so I expect this makes a difference.

[Paul Wagland]

Alice is spot on about temperatures at different heights above the ground. It's also worth remembering that this works on a larger 'garden' scale, as well as in the greenhouse.

For example, a depression in the ground will often 'fill up' with cold air and is the worst place to plant tender plants - veg or ornamental. Frost will also roll downhill - looking for the lowest point. This means that if you have a sloping garden with a hedge or wall across the bottom then the point where the ground meets the barrier will be prone to frost (as the cold air pools against the obstacle). Remove the barrier and you wont get frost there!

[Headfry]

also, it seems to get quite a lot colder just before dawn break!

[Paulottie]

I planted out some broad beans a couple of month back and put a tunnel cloche over them but there wasnt enough space so I have this perpect thing that is shaped abit like a cloche so I put it over the rest we had lots of frost gorund totally white and they still wernt affected even though it had totally open ends on it.

Broad beans are petty hardy. I sow direct in November with no protection (occasionally a windbreak helps) and again in March (with a bit of net to stop pigeons)...Grow them hard for sturdy productive plants.

Lettuce(most varieties) are best as a cool season crop. They are not Frost hardy exactly but will be perfectly ok with a bit of fleece or a bottle cloche. Infact I would say that the opposite is your problem here...should they heat up in that cloche during the day they may well bolt.

[Snadger]

............................... then the point where the ground meets the barrier will be prone to frost (as the cold air pools against the obstacle). Remove the barrier and you wont get frost there!

No.........Someone else will get it!