Grow veg

Sowing seeds directly into the soil – the thick and the thin of it

If you’re sowing seeds direct in the soil, should you sow them carefully and thinly or throw caution to the winds and chuck loads in?

I’ve talked quite a bit in my last two blogs about the pros and cons of growing your own vegetables from seed, and about direct sowing versus sowing under cover and planting out mature plants. Whatever your view on those topics, it’s almost certain that you’ll be sowing some of your veg directly in the ground, so in this blog I’m going to be writing about sowing density and giving a few tips to help iron out some of the difficulties of direct sowing. 

Firstly, sowing density. Seed packets often suggest sowing thinly and then thinning further to a set distance. The idea is that the distance suggested is the optimum to allow the veg crop to grow to it’s full, mature size. But is making a thin sowing and then thinning further always the best way?

Here are some of the pros and cons.

Sowing thinly and thinning the seedlings to the advised spacing when they’re large enough to handle (the usual packet advice)

Pros

Giving vegetables more room to grow usually means their growth isn’t restricted by competition for nutrients and water or by lack of space or light, so they end up being larger.

Sowing thinly means you’ll spend less time thinning out seedlings to the final spacings advised on the seed packet (assuming you’re going to do that).

Sometimes you can transplant the thinned seedlings elsewhere (although also see cons below).

Cons

If germination is poor you can end up with a very patchy row or can even find yourself in a ‘hunt the seedling’ situation as only one or two appear.

At this stage it can be difficult to see the beetroot seedlings in among the weed seedlings

It’s hard to see your row because the seedlings are tiny and spaced quite far apart, and unless you’ve really got your eye in it’s all too easy to lose a few when weeding.

Thinning can attract pests when growing certain veg like carrots and parsley (carrot root fly).

You get less of whatever crop you’re growing than if you’d sown more thickly (although it could be larger!).

Thinning seems wasteful if you’re just pulling out healthy seedlings and can’t re-use them, or if they don’t transplant easily.

Sowing much more thickly than recommended and not thinning them out at seedling stage

Pros

You’re much more likely to get a full row, even if conditions are difficult and germination isn’t 100%.

A thick sowing and healthy germination is giving some dense rows of seedlings in this large vegetable garden, but even here you can see gaps where germination rates have varied.

You can let everything grow to ‘baby’ size and start picking then, so you effectively thin out at a much later stage and can eat what you thin.

It’s a lot easier to see your row and you’re much less likely to accidentally hoe off your own crops when weeding (maybe this is just me, but I will assume others do this occasionally too).

It’s less work.

Cons

If germination is good your row can become massively overcrowded and the vegetables might not develop well, or they’ll grow into strange twisted shapes.

You need to sow a lot of seed which adds to the cost and you risk losing it all if something goes horribly wrong afterwards (dry weather, or wet weather and slugs).

So which technique is better?

Some of the most interesting conversations I’ve had about sowing and growing vegetables were with a man called Ramsay Shewell-Cooper. Ramsay, who was aged around 80 when I met him, had been a dedicated no-dig gardener all his life, having learned the techniques from his father, Dr WE Shewell-Cooper who started writing books on the subject in the 1930s. Ramsay had a demonstration vegetable garden at Capel Manor College which was next to the Which? Gardening trial garden, and I would often see him there tending to his flourishing vegetables.

Our conversations were normally short (we were both busy!), but his uncomplicated approach to growing didn’t take long to explain. My questions usually ran along the lines of ‘how did you manage to get that to grow like that’?! And his answer would always be a breezy comment along the lines of ‘Oh, I just chuck them in and away they go’.

When Ramsay sowed anything directly, he sowed much thicker than I’d ever done on my allotment. Sowing into a layer of compost, his seeds always germinated well, and his rows were soon thick with seedlings. I asked him about thinning but he told me he never bothered, he just let them grow and didn’t start removing anything until it reached a size it could be eaten. After he removed the first, small plants, the others grew on larger. I’ve done this myself ever since and it works very well with all my root crops and most leaf crops.

 

These rows of seedlings are quite dense, but there’s still plenty of room for development

What works best when sown thickly?

Carrots, parsnips, beetroot (especially if using monogerm seed, which only has one embryo per corky seed instead of the more usual three), spinach, kale (for cut and come again), leaf lettuces, rocket, parsley, chard, peas for pea shoots, chives, spring onions.

Which vegetables really need to be sown more thinly?

Lettuce that develops a head should be sown more sparsely and thinned out if needed to the recommended distance, or the head won’t get a chance to develop.

Bulb or Florence fennel needs room for the bulb (in fact it’s the base of the leaves) to swell.

Bigger vegetable plants such as peas and dwarf French beans should be given room to develop.

Sweetcorn needs to be given room and planted in a block for better pollination, so shouldn’t be sown in rows at all.

Ways you can make direct sowing easier

When I was manager of the Which? Gardening trial garden, I used to dread trials that involved direct sowing. Usually we were sowing annuals like sunflowers, nicotiana, poppies or calendula which have different sizes of seed but similar problems. Sowing depth can be hard to get right in open soil when you’re making a long drill. Then there’s the difficulty of keeping the soil moist after sowing unless you time your sowing well and get regular rain afterwards. This difficulty was even greater on the allotment because I wasn’t there as often. A spell of hot dry weather at the wrong time can ruin your plans but very wet weather isn’t always ideal, especially if you have a slug problem.

But there are ways you can make life easier, and I’ve done quite a lot of experimenting over the years so here are my suggestions.

Firstly, if you don’t want to dig and do the sort of soil preparation that’s normally recommended for direct sowing, you can avoid it by using a deep layer of well-rotted organic matter over the bed and sowing into that. Alternatively, as long as your soil isn’t heavily compacted you can create a slightly deeper drill than you need, fill half the depth with compost and sow into that.

Whichever way you choose, water the drill before sowing so it’s nice and moist underneath the seeds, and water again after you’ve covered them – covering the seeds with compost rather than soil helps to keep the depth consistent, which helps germination. If you don’t get rain, water your rows thoroughly once or twice a week. Don’t be tempted to water little and often as it won’t sink in to the soil properly.

Cut the grass recently? Use the grass clippings as a light mulch over your sown rows. This helps to keep the moisture in the soil and doesn’t have any adverse effect on germination as far as I’ve seen. You won’t need to water as often and all you will need to do is keep an eye out for the seedlings and make sure you move the grass off them as they come up so they get plenty of light. You can just move the grass aside and leave it on the bed and it will continue to help keep moisture in.

Pre-germination – Parsnips in particular can be very temperamental when it comes to germination. If the seeds are even one year old you might not get any coming up at all. Try pre-germinating the seeds on a couple of layers of kitchen towelling, kept just damp in a tray. When the tiny root emerges you can (very carefully) place the germinated seed in your row. You can do this with other seeds if you find them difficult to germinate (it also helps if you have an old pack of seeds and want to check they’re still alive, or if you suspect they’re a dud pack).

Slugs and snails can be a more difficult problem. Keeping your beds neat and tidy and removing any mollusc hiding places helps, but if you have an allotment you’ll find they’re probably hiding on neighbouring plots that aren’t as tidy, and they’ll walk a surprisingly long way for a row of seedlings. I sometimes use pellets made from ferric phosphate, which is thought to be much safer for the environment and for other wildlife than metaldehyde was (its now been withdrawn from sale) although it doesn’t kill as quickly as metaldehyde did so the condemned molluscs might still enjoy a last meal. Nematodes, a biological control that’s watered into the soil, are a more natural and effective way of dealing with slugs, but don’t work with snails. I also mulch my beds with ‘Strulch’, a mineralised straw that they don’t seem to like crossing. I’ve never found any other physical barrier that works.

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