Winter crops in protected cropping
Growing Leafy Brassicas
Broadcast in growbags or pots
Seeds of leafy brassicas can be broadcast in growbags or pots sometime during the first two weeks in September. Though it is probably more convenient to do the sowings inside, they can be also be made outside – preferably at the beginning of September – before moving the pots and growbags inside, doing so up to the middle of October. See Easy Peasy Gardening for tips on growing leafy greens in containers.
Grow as single plants in either growbags or the ground
Leafy brassicas can also be grown as single plants by directly sowing the seeds into growbags or the ground inside a greenhouse or polytunnel, preferably during the first half of September. Alternatively, they can be started as transplants by sowing the seeds in module trays. If done this way, the transplants can be raised either indoors or outside, although plants raised indoors can be sown somewhat later:
- Raising transplants outdoors: sow the seeds towards the beginning of September.
- Raising transplants indoors: sow the seeds about the middle of September.
Sowing into modules; Broadleaved Mizuna module ready for transplanting.
Regardless of when and where the transplants are produced, they should be transferred to growbags or the ground in a polytunnel or greenhouse sometime around the middle of October.
Michael transplanting Oriental brassicas into a polytunnel in October.
As a rule of thumb, leave about 20cm between plants. The plants can be harvested at virtually any height, though we tend to wait until they are at least 15 cm tall. Either harvest the larger outside leaves, allowing the ones towards the centre of the plant to grow larger, or cut all the leaves at once, leaving about a 3cm stubble above the soil surface and letting the leaves regrow before cutting again.
Harvesting Joi Choi by cutting all the leaves; stubble left behind after the cut iwth the immature leaves in the centre ready to regrow.
Harvesting will generally begin about the latter part of November and continue until March or April, when the plants will start to bolt. Even then, both the leaves and stems are still tender enough to eat.
General care through the winter
- Be sure to vent your greenhouse or tunnel on warm days. This allows some heat to escape while refreshing the air inside.
- Watering plants during the winter is done much less frequently than during the summer. The rules, however, are the same: keep the soil and compost moist but not wet, and don’t allow the plants to wilt.
A word about fertilising overwintered greens: Overwintered plants grown in the ground won’t need to be fertilised – there is enough residual fertility from the summer crops to get them though the winter.
Plants grown in compost-filled growbags and pots are another matter when it comes to fertilising, and we are uncertain about the advice to give. Certainly, the compost has enough fertility to support growth for at least a month. Then after that, the plants should be periodically given a liquid feed containing micronutrients. At this point, our skill set comes up short since we are not sure how often ‘periodically’ is. We do know, however, that some caution must be exercised: over-do the feeding, and you end up with lush growth that may be rife with nitrogen (see below); under-do it, and you won’t harvest enough leaves to make your efforts at growing worthwhile. So, do what we do and wing it until you get enough experience to make a judgement call.
Before you proceed with overwintering greens, we must warn you of the potential health risk associated with the accumulation of nitrates that can occur under low light levels. Though we relish our greens through the winter, we don’t know ourselves the full extent of the risk. We have, however, made a somewhat informed decision that we would eat them based on some knowledge of the facts, and to give you the same opportunity, we suggest you check the links given below:
For a more recent and comprehensive account, read the following: www.efsa.europa.eu/en/scdocs/doc/689.pdf
A good crop of Oriental leaves in a polytunnel.
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In addition to leafy brassicas, peas are another option for overwintering in a tunnel or greenhouse. They are not as easy to grow but can still provide a relatively effortless harvest when other vegetables are in short supply.
Sowing peas into a gutter and directly into the ground.
About the middle of October, we direct sow our pea seed in single rows, leaving about 3 cm between seeds. Sowing can also be done in compost-filled gutters, which are then transplanted into the ground as soon as the roots fill the compost. Be sure to keep an eye out for mice, setting traps if there are signs that the seed is being dug up and eaten.
Under the low light levels of winter, pea varieties grown inside are taller than they normally are when grown outside during the summer. Consequently, naturally tall varieties such as Sugar Snap can grow up to 3 metres or more. Because they are so tall, the vines need to be trained upwards if all that growth is be managed properly, otherwise, you will end up with a jumbled mass of vines that makes picking difficult if not impossible. Pea netting, available in nurseries and garden centres, is ideal for training peas, though other types of netting will do just as well.
Overwintered dwarf peas such as Sugar Ann, a sugar snap variety, also grow taller than normal when inside a greenhouse or tunnel. Fortunately, the vines are still short enough to grow along the ground without getting too tangled up. However, if you have only a small structure, it may be a good idea to contain the growth by training the vines just as you would for the taller varieties.
Harvesting will begin sometime in the early spring. It ends quite early for the dwarf Sugar Ann, but can go on until May or June for the taller varieties such as Sugar Snap and Carouby de Maussane.
Sugar Snap peas ready for harvest (left): Carouby de Maussane flower (right).
© Michael Michaud