[BJB]

I'm new to the allotment and have noticed a lot of people are using plastic bottles over their crops.  Can anyone tell me the reasons for this and which crops are aided by this method

[muntjac]

bottoms cut off large plastic bottles act as mini greenhouses and can be used to protect cabbages etc sweetcorn  from frost.. just remember to water the plants with the bottles removed. and welcom to the world of growing food

[BJB]

Thx
Do they help deter slugs at all?

[Yorkie]

Ooh, that's a good question  

There are likely to be two main reasons:

1. Slug defence (overground slugs only) - to prevent slugs and snails from nibbling the plants, particularly when young, tender and fragile.

2. As cloches - to keep the temperature round the plants up by a couple of degrees when frost is threatened.

Hardy plants like onions, garlic, parsnips, carrots, peas don't need the frost protection.  I wouldn't use the bottle method against slugs for peas either - too many peas and not enough space.

I've seen it used round lettuces / salads, and brassicas at this time of year.  I'd suggest taking care that there is still some air circulation and space between the plant and bottle sides or you will risk fungal diseases.

Non-hardy plants such as tomatoes, sweetcorn, courgettes, beans, shouldn't go out until the frost risk has passed so I wouldn't advise its use for them at this stage.