Non-stop crops: get multiple harvests from containers
by Mark Ridsdill Smith
Growing three or more different crops per container in a year is not difficult, it just takes planning
There are many rewards to be had from growing food in containers, but getting a worthwhile harvest from a small space can be a challenge. My first attempt at balcony growing resulted in one solitary serving of rocket. Fortunately, it’s possible to get a year-round supply of fresh vegetables and leaves from your pots, if you just devote a little bit of time to planning.
There’s plenty to be learnt from historical examples of urban farming. In the Nineteenth Century, before refrigeration and national rail networks, vegetables had to be grown locally if they were to be eaten fresh. To meet the high level of demand in cities, urban farmers developed ingenious ways of growing food intensively on small plots of land. As well as copious supplies of manure, the big secret of their success was planning. They knew exactly how long each crop took to mature. Then, when harvested, the space would immediately be filled by another crop, carefully grown to be ready to plant out just in time. In the suburbs of Paris, the French farmers became masters of this technique. They regularly managed to grow five or more crops on each bit of land every year.
French Intensive Farming, as it became known, is a highly skilled business. But growing three or more different crops in a container per year is not difficult, it just takes planning. The trick is to start the year by growing a crop that matures early, following it with a main crop over the summer, and then replanting the pot with autumn and winter crops.
Peas are one of my favourite early-maturing crops. If planted in February or March, they’ll be ready by June or July when they’ll make a welcome addition to the dinner table, singing of summer on its way. (I’ve found that mange tout or snap-type peas give significantly better yields from containers than podded peas.) First Early or Second Early potatoes also grow in just three months, ready for harvest in June or early July. Although potatoes take up lots of space, they taste so much better than shop-bought that it’s hard to resist growing a few. Other crops you can harvest in June or July from a March sowing include mini beetroot (ten to twelve weeks to harvest), chard (ten weeks), carrots (fourteen weeks) and turnip (eight weeks).
Your choice of your first crop of the season will be influenced by the second. Even peas and Early potatoes will not be ready in time if you want to plant your tomatoes out before the end of May. In this case, your alternative is to choose an even faster-maturing crop, or ‘catch crop’, to start the year. Good early season catch crops for containers include radishes (three to four weeks to harvest), pea or broad bean shoots (two to four weeks), rocket (six to eight weeks), coriander (six to eight weeks), and many of the Asian greens like pak choi, Chinese cabbage and choy sum. Started under cover in February or outside in March your crop will be ready to harvest by April or May.
As your first crops of the year mature, you can save further valuable space and time by starting the next set of crops in seedling trays or small pots. This means that when your first crop has been harvested, you can immediately replace it with a seedling or small plant.
Your second crop will usually be your main one of the year. Tomatoes, aubergines, and peppers ideally need to go in before the end of May. Courgettes, squash, French and runner beans, on the other hand, can be transplanted as late as the end of June, even mid July if started first in pots. Carrots, beetroot and spring onions can be sown in July – sow direct or raise in modules because root vegetables do not like their roots disturbed.
Crops like courgettes and squash will become quite large when mature so you need to give them lots of space. This means that when you first put in a baby courgette, there will be empty space in the pot until it grows. So another trick is to plant seedlings of a very quick-maturing crop, like rocket, around the baby courgette plant. Simply harvest the rocket as the courgette grows and takes over.
August and early September is the time to start sowing your third crop in trays or pots, ready to go into the container when the second crop has finished fruiting in late September or October. The idea is to get your third crop well established before the coldest months set in – this will help it to survive the winter. Good winter crops for containers include kale, chard, cavolo nero, mooli, and winter salads like lamb’s lettuce, winter purslane, winter lettuce, and land cress.
When growing intensively in a small space, it’s vital to ensure that you maintain fertility in your containers. Remember to mix in fertiliser or fresh compost or manure between each crop. I also always add a handful or two of worm compost from my wormery – this adds valuable microbes as well as nutrients and organic matter.
And as with all rotations, you need to consider the sequence of crops. Don’t grow the same crop in the same container again and again or crops from the same family (so don’t follow potatoes with tomatoes, for example). Crops from the same family have similar nutrient needs and will deplete the soil faster. Planting different crops also helps to avoid build up of pests and diseases. And try to follow a hungry crop like courgettes with a less demanding one like rocket.
By using this technique you can eat green leaves and vegetables for twelve months of the year, even from a small space. I’ve progressed from growing one pot to over ten kilos of rocket and other salad leaves on a nine foot by six foot balcony, as well as over thirty kilos of beans, herbs, tomatoes, courgettes and other vegetables. And not only will you get a substantial harvest,you’ll also put an end to lifeless empty pots in winter and create colour and life in your containers all year round.
Example year-round planting plan for four pots:
Dates refer to transplant dates – seeds should be started two to four weeks earlier.
Mark Ridsdill Smith is founder of Vertical Veg, a social enterprise that inspires and supports people to grow food in small urban spaces. As well as growing over £800 of food on his balcony and window sill last year, Mark runs container growing workshops, and gives talks. You can read more about Vertical Veg and his latest vegetable exploits at www.verticalveg.org.uk.