For many vegetables, there are considerable and fascinating benefits from sowing two or more seeds together, as opposed to a single seed per module or station. Here we look at multisowing in module cells, three to ten seeds per clump, according to the vegetable.
You can do the same with direct sowing of larger seeds in the ground, using a dibber to make shallow holes for each cluster of seeds; whereas for small seeds like carrots, sowing direct in rows is easier and generally gives close spacings.
Benefits of multisowing for transplanting
There is much to gain. Multisowing is an excellent use of time, space and materials, and you are rewarded with happier plants that germinate and grow more strongly.
- You can raise more plants in the same area of propagating space.
- You save time because you are transplanting two or more seedlings at once.
- Four-seed modules need three-quarters less compost to propagate the same number of plants.
- There is a companion effect – observe how well plants grow from being with their friends in clumps.
Root vegetables that can be multisown
The term ‘root vegetables’ is often used in a misleading way, because it is a generic, rather than botanical, description.
I don’t like hearing it used in descriptions of rotation, which is about growing vegetables of the same plant family in a different space each year.
Root vegetables are from many families, and grow in two different ways. Multisowing works best for the second group.
- Parsnips and carrots make unforked taproots from direct sowing, which is the part that we eat. They still grow as transplants, and carrots are indeed feasible in clumps, but they tend to grow with forks and are therefore less pretty at harvest, as well as being more difficult to clean. The same applies to salsify, scorzonera and Hamburg parsley.
- All other root vegetables swell nicely after transplanting, and the part we eat is actually a swollen stem or bulb, sitting above the system of plant roots (see the photo of celeriac below). The act of transplanting disrupts a taproot and results in more fibrous roots below soil, but this does not affect growth of the bulbs.
Celeriac and swede are root vegetables that you can transplant, but which grow best as singles. They need more space to reach a worthwhile size than, say, beetroot and onions.
Beetroot
This is a classic. I have been growing multisown beetroot since 1983, and always appreciate the extra harvest and ease of growing.
The most productive number in a clump is four, but it’s not obvious how to achieve precisely this. Beetroot seeds are actually clusters themselves! Botanically speaking, these seeds are fruits.
- One seed may grow as many as four seedlings, and some beetroot seeds grow just one beetroot, or may not germinate at all.
My preferred number is three seeds in a module, thinned to four seedlings. Three seeds means that all modules should have the desired number of four plants, after your thinning.
Florence fennel
Fennel transplants very nicely, and grows well in clumps of two or three. Generally, however, I transplant single fennel plants, even from pricked out seedlings, because I want fatter bulbs.
If you are happy with smaller bulbs, and more of them, multisow three seeds thinned to two plants.
Garlic
This is new for me, as of summer 2021. The previous autumn, when planting garlic bulbs in the polytunnel between lettuce transplants, we somehow managed to drop two, or even three cloves in some of the holes.
I noticed this when they first emerged, and was curious to see the results during our June harvest.
Where there were three garlic bulbs growing together, they grew to a smaller but still very respectable size, and altogether there was more weight of harvest.
Every year, separately to this, I have been planting garlic a little closer than in the previous year. There is plenty more to learn here, but it appears that, unless you want monster bulbs of garlic, close spacing and multisowing look worthwhile.
Onions for bulbs
This is another classic vegetable for multisowing. Seedlings enjoy the company of their mates and they all ease upwards in a supportive network of dense leaves. The harvest is of many medium bulbs, plus a few small ones, as opposed to fewer large onions if you grow them as singles.
- A caveat is onion mildew from close planting – you would see a grey mould on the leaves in the damp weather of early summer. In dry regions this is unlikely to be a problem, but, if concerned about it, sow Hylander or Santero (both F1), which have resistance to Peronospora destructor – a horrible name and a horrible disease!
- It helps to thin clumps by mid-May – we remove the smallest plants for eating as spring onions. My preference is four onions per clump (after having sowed five or six seeds), but this method works well with more, or fewer. All onion plants can be eaten at any stage, whatever they are called.
Onions grow in cool conditions, so it’s fine to plant them even when there are still night frosts. They establish a strong network of roots which then power amazing growth in the long days of late spring. You can almost see them grow, and I love them for that proud sheen on their upright leaves.
You can multisow onion sets, although it’s as easy, and almost as effective, to plant them closely, with as little as 7.5 cm / 3 in between each onion.
Radish and turnips
Because multisowing allows you to grow more plants in the same space, it’s time-efficient to grow early crops at a time when warmth for propagating is scarce and precious. Harvests of radish and turnips in April and May are welcome as ‘hungry gap’ vegetables, when there is little fresh food. You then have time to clear the crop residues before plantings of summer beans, courgettes, brassicas etc.
When radish grow in the cool conditions of early spring, they have a softer flavour and less pungency compared to harvests of late spring and summer. Likewise, early turnips are sweeter than harvests in early autumn. After you transplant them, lay fleece over to speed up the early growth. They are frost hardy but grow faster when protected, and fleece also protects these plants from pigeons and most flea beetles.
Early sowings under cover also give you the chance to pop transplants in the gaps between wider-spaced vegetables, such as peas and potatoes. The eventual harvests from the interplants you see in the photo below were 0.9 kg / 2 lb of Rudi radish through April, and 1.5 kg / 3.3 lb of Sweetbell turnips from late April until early May. The space between them was then quickly covered by potato leaves.
- You can multisow turnips in August and radish in September, to grow a late crop after clearing any summer vegetables whose harvests have finished. Or transplant them between any vegetable that may be finishing soon, if there is space available.
Leeks
The best result of multisowing leeks is a higher amount of harvest per area. I almost weep when I see leeks given what I would call ‘traditional spacing’, with huge areas of wasted potential between each plant.
Multisown leeks contradict some common assumptions about how to grow them:
- Transplants don’t have to be set deep in soil.
- They grow well in clumps, with slightly curved stems and a higher yield per area.
A consequence of the first point above is that stems are pale green rather than white, from developing mostly above ground level. If you desire a long white stem for every leek, it’s best to raise transplants in open ground and to set them in more deeply.
I used to set leeks deep in the soil, which takes more time, both when planting and when harvesting. Also, I find that growth of transplants is faster when their roots are closer to the biologically active soil surface.
- In regions of cold winters, below about –8°C / 18°F, leek stems that are deep in the soil will freeze less. Leeks resist frost, but long stems above ground do risk damage when it’s very cold.
Two lovely results from not setting transplants deep in soil are that there is little soil or compost in the leaves where they join the stem, and that it’s easy to pull leeks at harvest. You may need to use a trowel to cut around the rootball, with downward pushes near to the stems. This leaves most roots in the soil and causes less disturbance.
Onions for salad leaves and stems
Spring, or salad, onions have been bred to grow longer stems and with a later development of bulbs, often of less pretty shape. They are fantastic for multisowing because you can grow so many in a clump. I suggest sowing up to ten seeds per module cell (twice as many as with onions for bulbs), then, at harvest time, either twist out larger ones successively or pull the whole clump. Use a trowel to undercut the roots in order to disturb soil less.
Some varieties are ‘dual-purpose’, as with Lilia. I like Lilia for its colour and flavour, especially when harvested as spring onions. Plants left to grow until late summer make decent bulbs, but the variety is prone to mildew, and a few plants may bolt (flower) in early summer. Remove bolters as soon as you see them, to eat soon after, because the plants stopswelling once flowering initiates.
The main harvest period of spring onions intemperate climates continues from spring to autumn, depending on when you sowed them. Once bulbs start to form, the tenderness and colour of their green leaves decreases. If you want fresh green onion leaves, it’s best to sow every six to eight weeks.
Oriental vegetables and rockets
Most of these are for eating as salad leaves. The main exceptions are pak choi / bok choi, and tatsoi, which are usually grown larger and used in cooking. For this purpose, sow two seeds and thin to one plant per station.
Wild rocket also grows well as a single. This is a little ironic because its leaves are small, and early growth is strong when two or three plants are clumped together. However, if you want a long period of harvest from, say, April to July, usually from a September sowing, I have found that one plant spaced at 30 cm / 12 in continues to grow more strongly than two or three plants clumped together.
The other plants of this category, which include mizuna, mibuna and salad rocket, grow nicely in twos and threes.
Peas
Peas need space for an extensive root run, but they germinate and grow strongly in multisown clumps.
- Your eventual spacing at transplanting depends on the type of pea, which governs its eventual height, and on whether you are growing for pods or shoots.
I sow three peas for two to three plants when growing for pods, and four to five peas when growing for shoots. Remember to keep a mousetrap nearby when sowing peas, as well as at the transplanting stage – rodents may nose under the seedlings to eat those germinated pea seeds.
Spinach
This is true spinach, not leaf beet, and, as with chard, you have many choices. The main variation is to grow more plants per clump when you want smaller spinach leaves for salad.
Single plants of spinach can grow impressively large leaves. In no dig soil these are still tender and sweet, and quicker to harvest for a given weight of leaves.
Spinach can be an impressive staple green for harvests even in winter, when leaves also grow sweeter.
Multisowing is not always the best option
Vegetables not detailed here make better harvests as singles; for example, cabbage and lettuce to make hearts (heads), swede and celeriac to make large roots, celery to make juicy stems, and cucumbers to grow fruits of decent size.
Likewise, it’s easier to pick the outer leaves of single lettuce plants than of those in groups of two or three. On the other hand, it works well to pick larger leaves from two or three salad rocket plants in a clump. Try a few numbers to see what you are happiest with.
- Broad / fava beans are an exception because they ‘tiller’, making many stems from one seed, so they are best sown as single seeds and given space to develop. As they grow, it looks like you have multisowed them.
Multisowing guide
- The numbers shown are for medium-sized plants and a high yield.
- The desired number of plants in a clump is your choice, according to the size of plant you wish for, and how you like to harvest the leaves.
- The first column shows my suggestions for how many seeds to sow per module. These numbers are higher than those in the same row’s second column, to allow for some seeds not germinating. Also, some grow weakly and are best removed.
- The second column shows how many plants per clump can grow to a worthwhile and harvestable size, in my experience. Beetroot and chard are exceptions because their seeds are in clusters, often germinating more than one seedling.
- The spacings shown in the third column are absolutely not fixed and are just suggestions, based on having ‘average’-sized harvests. Feel free to try slightly closer orslightly wider spacings.
