Cucumber Leaves

[roogrow]

Morning all,
has anyone come across the leaves of cucumbers cracking at the edges like on the image, I have several and they are all the same, there are brown blotches too near to where the leaf joins the stem... I have been really careful to not over water and they are in a fairly big pot for their size- I am baffled.

Cheers

[nickdub]

I wouldn't worry about it as it's only the seed leaves which seem to be slightly busted at the ends - the new main leaves are fine and the plants generally look very healthy. Not sure what caused the damage, but sometimes with these large seeds the outer casing doesn't fully split after germination has occurred, so the cotyledons have to force their way out of the shell.

[roogrow]

I wouldn't worry about it as it's only the seed leaves which seem to be slightly busted at the ends - the new main leaves are fine and the plants generally look very healthy. Not sure what caused the damage, but sometimes with these large seeds the outer casing doesn't fully split after germination has occurred, so the cotyledons have to force their way out of the shell.

That's reassuring, thanks very much. Fingers crossed I can plant out next week! I'm thinking I might use cut up fizzy pop bottles to put over as a cloche just incase it gets a bit chilly - any successes with this before? Seen pics of it and it seems a good idea in theory...

[nickdub]

Yes plastic cloches definitely work but there are limits. One is that the extra temp is generated by the sun, so if you have a dark and frosty night then the cloche probably won't be enough protection to save your plants - I'd advise potting these cucs on into larger pots and keeping them indoors for a bit longer, especially considering the weather forecast. Another issue with small plastic cloches is that the plants soon get too big for them, particularly courgettes as though grow really quickly but cucumbers either grow quickly too at this time of year or fail altogether and die. Having said all that if you can get enough giant plastic containers say the 4 pt milk ones or larger (they only have to be translucent not necessarily clear) and use them, that is a better bet.

The best fit for 1L plastic water bottle cloches is sweetcorn - just the right shape and if you cut the top off as well as the bottom later in the year you can just leave the bottle on as a sort of high collar, so that the plant gets a little extra warmth and a bit of protection from slugs etc.

Happy gardening - Nick :-)

[ameno]

Yes plastic cloches definitely work but there are limits. One is that the extra temp is generated by the sun, so if you have a dark and frosty night then the cloche probably won't be enough protection to save your plants

That's not strictly true.
Obviously there are limits to what they can do - you should expect 2c extra protection at most - but the frost protection by cloches, and indeed fleece, is not actually due to trapping the sun's heat. Rather, it is because they trap the heat given off by the soil. This time of year, the soil is 10c or more, and it holds onto this heat for a long time, so if you can trap the heat radiating from it at night, with a cloche or fleece, it can help warm the air and prevent frost damage.

[Penellype]

That's not strictly true.
Obviously there are limits to what they can do - you should expect 2c extra protection at most - but the frost protection by cloches, and indeed fleece, is not actually due to trapping the sun's heat. Rather, it is because they trap the heat given off by the soil. This time of year, the soil is 10c or more, and it holds onto this heat for a long time, so if you can trap the heat radiating from it at night, with a cloche or fleece, it can help warm the air and prevent frost damage.

If you apply cloches or fleece when the sun is still on the area then some of the heat will be trapped and will take longer to dissipate than it would have done without the cover. The ground also acts like a storage heater, radiating heat slowly over night, and as you say, this heat is trapped for longer with a cover.

However, it isn't as simple as that, because it depends on the cause of the cold. If the air is below freezing (air frost) any trapped heat inside the cover will help to keep the temperature a little higher, which may be enough to save the plants, depending on the degree of frost. On still, clear nights within a cold air mass the danger is ground frost, which is caused by sinking cold air not being stirred up by wind. The air at the surface becomes significantly colder than the air temperature even a few feet higher and can cause the ground to freeze and damage plants in temperatures upto about 3C. In this case covering plants will stop the air sinking onto the leaves and damaging them and you may find a layer of ice on your cover in the morning. The radiative warming effects will still be there as well.

The most difficult situations are when it is cold and wet and/or windy. Wind causes water to evaporate and this has a cooling effect which can tip the balance towards damage if the air is already quite cold. Anchoring covers in these conditions is challenging, and the covers will only work if the cover is not touching the plants, particularly if it is wet fleece, which tends to stick to the leaves and freeze onto them.

[nickdub]

I agree with Penellype's good explanation of gardening/frost etc from a scientific pov - for beginners I'd just say keep your tender seedlings inside until all risk of a frost in your area has gone by, unless you have a substantial structure to put them in like a well insulated cold frame or heated greenhouse of course.

-As an example of the sort of damage frost can do, even in large relatively warm structures I had a frost of about -1 here 3 weeks ago. Outside in my large (6m x3m) poly tunnel all the plants were fine including the grapevine which had put on a lot of new green growth except for the bits of that growth that were touching the plastic roof. Those green bits lost heat to the outside via conduction, so were frosted, turned brown and are now dead.

[roogrow]

Thanks everybody for the really informative responses! Lots of food for thought.
I do have a brick built stand alone garage and so may have to resort to there, as my kitchen window is overrun.
the garage does have a double glazed window which is SW facing so will get some sun in the day. Fingers crossed this week will be the last of the cold. Thanks again