What to Plant in your Polytunnel or Greenhouse in March

While March is still too early to plant much in outdoors beds across most areas, March is a great time to plant things in your polytunnel or greenhouse, or to transfer some seedlings grown indoors into unheated, under-cover areas. While the weather outdoors can be far more erratic, offering anything from snowy to sunny, in the polytunnel or greenhouse things can really begin to heat up. Towards the end of the month you will probably have to start thinking more seriously about ventilation and leaving doors open on a clear, sunny day. Your watering will have to be stepped up.

If you have been growing winter crops in your greenhouse or polytunnel over the colder months, you may have quite a lot already growing in there when March rolls around. You may well have hardy leafy plants such as salads, Chinese vegetables, chard, or perpetual spinach growing slowly over the winter. These types of plant will potentially still give you a yield in March. However, your mind should also turn to successional planting, so you ensure a continued supply of these leafy crops throughout the year.

Wherever you do create space for spring crops by clearing out some winter stragglers, it is a good idea to add some compost or semi-composted material on clear bed areas. Look out for slugs and snails and make sure that you have taken organic measures to reduce the potential for serious damage to your plants in the spring.

In March in your greenhouse or polytunnel you will be seeing over-wintering peas and broad beans begin to shoot up as the weather warms. You can direct sow some mange tout peas for early summer cropping, though bear in mind that things planted in March will often not be ready until mid-June, which is too late for you to harvest then clear them to make space for tomatoes and other heat-loving summer plants.

You can also direct sow carrots, beetroots or turnips, radishes and a range of leafy salad crops, though in March these may need to be covered to allow the temperatures to climb high enough for germination in more northerly reaches. Again, consider what you want to have in the greenhouse or polytunnel in the summer months and whether you have time to sneak in a quick spring crop before heat-lovers take over the space.

Ideally, you will already have sown seeds indoors in January and February and some of the hardier of these seedlings should now be the perfect size to be transplanted into their spots in an undercover but unheated space. Remember to harden off plants before exposing them to much colder temperatures and keep cloches and fleece on hand for any sudden frosts that will likely still threaten.

If you have enough space, you may have planted first early potatoes in your greenhouse or polytunnel last month. When the foliage appears, make sure you cover it with fleece if frost threatens. Bear in mind with everything you do in your greenhouse or polytunnel that the weather may be warming up a little, but we are not out of the woods where sudden cold snaps are concerned.