Grow veg

Sowing vegetable seeds Direct sowing or sowing under cover: which is better?

If you’ve got an allotment or vegetable patch and you’re going to grow most of your crops from seed (see my previous post for ideas on how to get plants if this isn’t an option for you), then it will soon be time to get started.

After you’ve decided what you want to grow, and have somehow managed to order far too many packets of seeds because you saw a few extra things that looked interesting, you can then enjoy the process of looking through all your packets and working out when and how you’re going to sow them. With some types of plants the approach will be obvious – they need heat and an early start so you’re going to sow them under cover – but with other types of plants you have a choice of sowing under cover in a greenhouse or on a windowsill, or sowing directly outside in the soil. Even some tender types of veg can be direct sown if they’re fast maturing enough to be sown after the risk of frost is passed.  

In practise, with seed sowing as with so many things, what works best for you will probably depend on your situation. I’ve been growing vegetables for a long time both on my allotment and at work so I’ve developed my own way of doing things, but what I’m aiming to do here is give the pros and cons and a few suggestions that might make your sowing more successful, whichever way you do it. If you’re an experienced veg grower you’ll have your own favoured way of doing things, but it’s always worth revisiting and maybe trying something different.

Pros and cons of direct sowing

Pros:

It’s saves work because you just sow straight in the ground and let the seeds grow (hopefully).

There’s less root disturbance with direct sowing because you’re not moving them. Plants grow steadily without the check in growth you tend to get when pricking out or transplanting so they get established faster.

You don’t need a lot of indoor space to sow and keep seedlings as they grow to planting size.

It is cheaper (and probably better for the environment) than sowing under cover because you don’t need lots of pots/trays etc and you don’t need to buy compost.

Cons:

Soil needs to be well prepared and fine, especially for small seeds like root veg and lettuces so you get the sowing depth right and the tiny roots and shoots can get through.  

Alternatively, you need to add a decent layer of compost (home made is fine, no need to buy bags) to the soil and sow into that (5-7.5cm). This is good for the soil as well, so it’s always a good idea as long as you’ve got enough compost.

Germination is more erratic when you sow direct for a variety of reasons, including the difficulty of getting sowing depth right, and temperature and weather changes.

In hot dry weather, which we can get even in March, you need to water regularly to stop the soil drying out. If seeds have germinated, small seedlings are very vulnerable to shrivelling up in hot weather.

Small seedlings are very attractive to slugs and snails. Sometimes they eat the lot.

Peas and bean seeds are very attractive to mice and they can get eaten before they germinate.

Seedlings are easily swamped by weeds, so if your plot tends to be weedy, you’ll need to keep on top of them in the crucial early weeks of growth.

Pros and cons of sowing under cover

Pros:

It’s easier to sow into compost in a tray or pot than into soil. The structure of a good compost encourages good germination, so you should get far more of your seeds to come up.

Seeds often germinate faster because they’re in a warmer place and the temperature fluctuates less between day and night than it does outside. 

Growing conditions such as temperature and moisture are more easily controlled.

Keeping pests at bay is easier, although you can still lose a few seedlings to molluscs if you’re not vigilant.

If you’ve got heavy clay soil, if you get a late, cold spring or if it’s just tipping down with rain day after day, sowing under cover allows you to get started without having to wait for conditions to improve and the soil to be more workable.

Sweetcorn seedlings just poking through the compost

Cons:

There can be more problems with disease if you don’t make sure you’re using clean pots and trays etc, or if the ventilation is poor.

You can still have problems with temperatures being too cold at night if you’re using an unheated greenhouse or too hot during the day on a sunny windowsill (or in a greenhouse if you don’t have enough ventilation).

You must remember to water even if it’s raining cats and dogs outside.

That roughly sums up the basic pros and cons.

Re-reading I wonder if I’ve made it sound as though sowing direct is the better option. In some ways it is better, but I certainly don’t think it’s easier. For me, especially as I grow veg on an allotment which I sometimes only visit once a week, the problems I’ve had with direct sowing outweigh the benefits. Perfect growing conditions are rare and the difficulty of keeping the soil watered after sowing, getting even germination and stopping slugs and snails eating seedlings have all led to me preferring to raise my veg at home in a greenhouse and then planting it out. But of course, I realise that isn’t an option for a lot of people.

Here are some suggestions for what works and what doesn’t that are based largely on my own experience but also on various conversations I’ve had with other veg growers.

Seeds that are best sown direct

Root veg – especially carrots and parsnips because of the tap roots, but also beetroot and radishes. Although you can sow all of these in pots and prick them out, carrots and parsnips will usually grow better without root disturbance. Also, all of these are easy to grow from seed (it can help to pre-germinate parsnips but I’m not going to get into that here). By the way, you can of course grow a lot of veg, including root veg, in large pots from seed to harvest, but here I’m comparing the different ways of starting off soil-grown crops.

The first beetroot seedlings, with some weeds keeping them company

Peas. Sometimes I’ve grown these in modules or pots and planted them out, more often I’ve sown them in guttering and then slid the seedlings into a trench. They’re hardy so you can start them off outside from about March or April.  But planting individual pea plants seems a bit crazy and they germinate in the soil easily enough so it can be simpler just to do that, especially when, as with spinach, you’re making a second sowing later in the year when the soil has warmed up. If you’re growing them for pea shoots you’ll want to sow densely, so it really can make sense to sow them directly. Watch out for mice eating your seeds, though. It might be best to put some into modules to plug gaps.

Spring onions. These are easy enough to sow directly, and you normally sow thickly as you’re going to pick them quite small, which makes it easy to see the rows as they come up.

These are just about the only crops I routinely sow directly.

Seeds that can be sown under cover or direct

Spinach, oriental leaf veg like pak choi, mizuna and mibuna.  Spinach is best sown successively because it tends to bolt. It’s worth making an early sowing under cover in February or early March so you can get some underway while the soil is still warming up, then sow seeds later on (from April onwards) directly in the soil. With pak choi and some other oriental greens, bolting can be a problem in hot, dry weather, so again you can make an early sowing under cover, then sow directly later in the summer so they’re growing through the cooler early autumn.

Lettuce. With lettuces that form a head I always sow in the cold greenhouse and transplant them outside when they’re a decent size, but for baby leaf and cut and come again, I tend to sow directly.

Chard. I sow chard in a tray and prick out into modules to grow on and plant out. I only want a few plants so there’s no point sowing directly. They’re easy enough to sow in the soil, though, and germinate well. In fact, I often find a few self-sown plants, so sometimes I let those grow on.

Leeks and onions. These take quite a long time to grow and the seedlings are tiny and quite hard to distinguish from blades of grass, so I always start them off in modules and plant them out. They can be sown under cover from February, and directly from around March or April as they’re fairly hardy.

Leek seedlings in a cold greenhouse

Brassicas – These are hardy, too, so although they’re slow to mature they can be sown outside from April which gives them plenty of time.  The advice used to be to sow them in a ‘nursery bed’ or seed bed outside and transplant them to the final position but I don’t know who that was aimed at. I’ve never had a seed bed myself and I don’t know what other crops you’d use it for. I always sow these into modules or trays and prick out, planting them when they’re quite well established to help keep the molluscs off them. You might only have room for a couple of plants so sowing direct seems wasteful, but you can sow them directly and if you’re growing kale or collard greens as baby leaf, or cut and come again it would be worth it.

Sweetcorn, runner beans, French beans, both dwarf and climbing and courgettes. I always start all of these off in pots in my greenhouse, but if you don’t have one, if you’ve left sowing a bit too late or you want to make a second sowing to get a later crop, all of these can be sown directly outside from mid-May, or whenever frosts have finished where you’re growing. For courgettes, a later sowing can mean you’ve still got plants cropping well when the early-sown ones are starting to suffer from mildew.

Seeds to sow under cover

These are mostly tender vegetables that need an early start, before the frosts have finished. Tomatoes, peppers, aubergine and cucumber. All of these really need to be sown under cover in March or April at the latest. Although they can be planted outside once there’s no more chance of frost they’re often better grown with some shelter throughout the summer, especially in colder parts of the country because they don’t cope well with cold nights or really dull spells of weather, which, lets face it, we can get in July and August.

Broad beans. I’ve separated these out from the other beans and peas because the timing is a different. To get an early crop of beans you need to sow seeds either in autumn or in January, which aren’t ideal months to be sowing outside. January might be impossible if the ground is frozen, so sowing under cover is best. For summer crops you should sow between February and May, so I’d suggest sowing into pots or modules from February to March, especially if your soil is cold and wet, and only sowing direct in April or May.

Any pre-May sowing of tender veg such as sweetcorn, beans and courgettes will need to be done somewhere frost free, so a greenhouse or a windowsill will be the best place to start these off from seed.

My next post will stick with the seed sowing theme, when I take a look at sowing density and how to make direct sowing easier for those things you have to sow outside.

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