Growhouse Features - Hardening Off Plants

By Author: Jean Vernon1
Total Articles: 31
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At this time of year a coldframe is an essential piece of kit for the greenhouse gardener. It becomes an interim stage between the greenhouse and the garden, but it performs an important function for plant health.

Plants that are raised in the protected environment of the greenhouse, even ones that are hardy or half-hardy, need toughening up a bit before they are planted out. Otherwise a windy afternoon or a cold snap will quickly take its toll. This also applies to plants that are bought from the garden centre.

A week or so spent in the protected but more exposed coldframe conditions allows the plants to acclimatise to the real weather outside of the greenhouse. Of course it's also essential to adhere to the needs of individual plants. It's no good germinating a range of frost tender seedlings and moving them out into the coldframe now, as it will just be too cold. A coldframe is just that, a cold unheated environment, and although some coldframes are better than others at insulating your plants, very few of them will protect them from frost. Experienced gardeners know the value in staggering sowing seeds, especially ...
... those that need warmth and frost protection. As the seedlings develop and are pricked out and potted up into large pots and modules, they take up more and more space. Hardy annuals and perennials can be moved into the coldframe prior to planting out, but the rest have to remain in the warmer climes of the greenhouse until the last frost has passed. In some areas of the UK this can be as late as June.

The secret with these plants is to sow them in late April and even May so that by the time they are large enough to be potted up and planted out, you can put them into the coldframe safely and plant them into the garden soon after. Another way is to sow them into large planters in the greenhouse that take up floor space rather than staging and shelving space and simply wheel or lift them outside on sunny days to toughen them up. You can then either take them outside when the last frost has passed and grow them on, on the patio, or grow them in the greenhouse for the rest of the season for an earlier crop. This works well for French beans, runner beans, tomatoes, courgettes and any other vegetables you can grow in containers. It can also be used for planters, hanging baskets and containers of flowers such as busy Lizzies, pelargoniums, petunias, in fact it is a very good way to prepare floral containers and displays ready to place outside in the garden when all danger of frost has passed. You can plant them up in March and April and keep them in the shelter of the greenhouse until the weather improves. You do need to harden them off before putting them outside in the garden, if they are too large for a coldframe then simply place them outside during the day, bringing them in later and later at night to acclimatise them to the colder air outside. Have a roll of fleece handy to throw over them when they are finally outside, in case there is a colder spell.

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