This super-close spacing is mainly for just a few fast-growing vegetables that are in the ground for weeks, rather than months. Sometimes these vegetables are called ‘catch crops’, because they ‘catch’ unused space before, after, and especially between slower growing plants.

You can transplant radish between newly planted potatoes, for example – the radish mature before potato leaves cover the whole space. Early turnips also work like this, for harvesting when the size of, say, a small plum.

Radish is one of the quickest vegetables to grow – transplant multisown modules of four plants each at 10 cm apart. Also use this spacing for spring transplants between early potatoes, and overwintered garlic. Or, for direct sowings, space at 3 cm in rows 15 cm apart.

At the other end of the spectrum from fast-growing radish is corn salad / lamb’s lettuce. It’s a small plant and never grows large, even with wider spacing. Winter is its best season, and 10 cm is a good average spacing for single plants.

For leaf harvests from vegetables and herbs of many kinds, I find a spacing of 22 cm serves four great purposes:

1. It affords enough space for plant roots to continue growing for many months, giving new leaf harvests for a long period from just one planting.
2. You have space to pick the leaves quickly and comfortably.
3. Harvests are of decent-sized leaves with plenty of flavour, and they store well if needed.
4. There is some bare space around every plant after each pick, resulting in better airflow, less mildew and fewer slugs.

You can grow plants for salad more closely than 22 cm, though not too close. Initial growth can look good, but later harvests become slow and fiddly with small and crowded leaves, some turning yellow where they are underneath other leaves. There may also be more mildew on lower leaves, and slugs living below them.

• A spacing of 22 cm is good for herbs like dill, coriander, basil and chervil.
• You can grow clumps of spinach, chard, and beetroot for salad leaves at 22 cm, or at wider spacings for large leaves to cook and beetroot for eating as roots.
• 22 cm is good for multisown spring onions, peas for shoots, and medium-sized heads of pak choi.

An exception to 22 cm spacing for salad leaves is when you grow plants for their heads. These need more time, and grow larger and healthier at spacings of around 30–35 cm. Examples are lettuce, endive (both frizzy and scarole) and chicory for radicchio.

This spacing works for several vegetables, including most multisown modules.

Multisown beetroot, single-sown sweetcorn

Individual beetroot plants need less space than sweetcorn, but a multisown clump of three to five beetroot seedlings grows nicely at 30 cm, just as sweetcorn does.

Incidentally, there is no reason to multisow corn, because we want large cobs. Also, corn plants often tiller with sideshoots from the base (see information below). One year I removed sideshoot stems to see how it affected growth; the main cobs were not much bigger, and I lost the small cobs of those secondary stems.

It’s reckoned that the best pollination of sweetcorn comes from planting in blocks rather than single rows. However, I find that pollination is still fine on cobs of quite isolated plants, when I grow them between squash as companion plants and for an extra harvest.

Broad beans and tillers

Broad beans look a long way apart when first transplanted or sown. The reason for a wide spacing is that each broad bean seed eventually grows into three to five stems, depending mainly on the sowing date, and on the variety.

New stems from one seed are called tillers. Their growth means that close spacing of broad beans initially looks wonderful, but results in fewer large pods. Also they are hard to find among the crowd of stem and leaf, and picking needs more time.

It’s best to check on growth when plants are, say, 60 cm tall, often by early May / before late spring, and to cut out a few stems if there is crowding in the middle of a bed.

Harvesting pods is easier when there is a little extra space between plants. You can achieve this by setting transplants at 20 cm apart, with 45 cm between rows across a 1.2 m /4 ft bed.

Early potatoes

First early types of potato grow so fast that they need less space than later harvesting types, and less mounding up as well. 30 cm is the closest that I would plant them, and sometimes we grow them at 37 cm.

The Vivaldi variety, for example, is sometimes called first early. However, it takes longer to grow than, say, the Rocket variety, and therefore benefits from a comparatively wider spacing.

In the bed of the two photos below, each row of four plants gave 7.5 kg / 16.5 lb of potatoes by the end of June.

Alliums

Leeks and garlic grow upright and with thin leaves, needing less lateral light than many other vegetables. You can grow them very close; however, this also results in small plants which take longer to harvest and more time to prepare in the kitchen, per weight of food.

The same applies to onions and, as they can be grown in so many ways and for so many purposes, I hesitate to give any one spacing. However, the main one I use is 30 cm between multisown clumps of four, for a harvest of bulbs in mid- to late summer.

Florence fennel

You can grow Florence fennel as an interplant and catch crop, popping in module plants wherever space arises, usually in late summer. Sometimes there is hardly any space when you pop in the plants but there is soon after, when, for example, cucumber or lettuce plants finish.

Spacing for bulb fennel is generally 30 cm, but it can be spaced as close as 22 cm – you would then need to harvest a few small ones to allow the others to grow large.