Start These Seeds in Spring or Regret It in Summer!

Most gardeners think spring sowing starts when the weather warms up, but some key crops will give earlier and more reliable harvests if you start them off sooner. I’m going to share how to start off five spring crops and give them the best conditions for strong growth – plus, we’ll find out how to grow perhaps the weirdest crop of all (honestly, it looks like it’s come from another planet!)…

Sow Tomatoes Early

I love to grow a range of tomatoes, from blight-resistant bush varieties outdoors to beautiful tall vining types in the greenhouse. That first tomato, plucked from the plant and popped straight into the mouth in one greedy movement, is pure ambrosia!

As a rule of thumb, you can start sowing tomatoes six to eight weeks before your expected last frost date. Sowing is super simple. Take a small pot and fill it with sifted multi-purpose potting mix, then tamp it lightly down using your fingertips or the bottom of another pot. If you’re sowing more than one variety, write up your labels ahead of sowing, because – I promise you from experience – it’s frustratingly easy to get hopelessly mixed up!

Sow seeds by placing each one on the surface of the potting mix at least a half inch (1 cm) apart. By taking a little care now your seedlings will have plenty of room to grow in those first days, which means you won’t have to rush to transfer them into their own pots before they start growing into each other – it basically buys you time.

Cover the seeds over with a little more sifted potting mix, label the pot and water it.

Tomatoes need warmth to germinate, so keep them under a humidity dome or propagator lid. If you don’t have one, just secure some clear plastic over the top. I like to germinate my tomatoes on a heat mat. This isn’t essential if you have a nice warm spot in the house to keep your sown pots, but it does dramatically speed up germination and gives a more consistent result. They don’t cost loads, so if you’re making lots of sowings of warmth-loving crops, I reckon a heat mat is a solid investment.

Once the seedlings are up, they can grow on a bit before being carefully transferred into their own pots. I like to bury the seedling almost up to the lowest leaves, as this encourages more roots to sprout from along the buried part of the stem and creates a sturdier plant.

Once the risk of frost has passed, the young plants can go out to the greenhouse to grow on before planting time. If you don’t know when your last frost date is, you can use our Garden Planner to look it up. It uses your local weather station to work this out, so you can have complete peace of mind when it comes to setting your plants out into the garden.

Just like when transferring seedlings into their own pots, plant your young tomatoes a bit deeper to get more of those supportive roots on the stem.

Grow Potatoes in Containers or Outdoors

Closely related to tomatoes are potatoes, both being in the nightshade family. If you’ve ever seen your potatoes flower and produce fruits, you’ll see the uncanny similarity (but don’t eat potato fruits – they’re poisonous!). What kitchen garden is complete without at least a few beds or even tubs of this crowd pleaser‽ I particularly love growing early varieties of salad-type potatoes. Those first, almost creamy spuds are heavenly!

Depending on where you’re growing, round about now is a great time to get your seed potatoes in the ground or nestled into their cushion of nutrient-rich potting mix.

If you get your seed potatoes ahead of planting it’s worth pre-sprouting, or ‘chitting’ them on a bright windowsill for a few weeks. Doing this is by no means essential, but it will speed up the time to harvest.

Potatoes are frost-sensitive fellows though, so at this early point in the growing season we need to exercise a little caution. But I reckon it’s well worth it for a precious early harvest! If you have a protected space like a greenhouse where you can mollycoddle your potatoes from plunging nighttime temperatures, you can get them started a lot sooner by planting them into large containers.

I love the simplicity of growing potatoes in containers. First, add a layer of potting mix (you can blend it with some garden compost to make it go further) to a depth of about 6in (15 cm), then pop in two seed potatoes. Top up with more potting mix so that it’s two-thirds of the way up the container, then add two more seed potatoes at 90 degrees to the position of the first pair so that the emerging shoots on the lower tubers aren’t growing into the plants above. What makes this method super simple is that there’s no earthing up needed – just finish off with more potting mix, filling all the way to the top of the container.

For an even earlier start, I like to bring my container spuds into the warmth of the house (on a tray to catch any water and soil that escapes) to get them sprouted before moving them out to the greenhouse. You can move containers outdoors once there’s no more risk of frost.

By the end of this month, where I am at least, conditions should be good enough to plant directly into the ground. A couple of weeks before planting, I place a couple of old windowpanes over the soil where I’m going to grow my potatoes to dry it out a bit and get it nice and warm. Anytime from autumn up until planting time, add plenty of compost on top of the soil to nourish it in advance of this glorious moment. And it is glorious – somehow planting potatoes feels like a true springtime job! The spuds are going in, the birds are singing, and life’s good, right‽

Dig a hole for each potato to a depth of around 6-8in (15-20 cm), then pop in your seed potato, sprouts facing up, 16in (40 cm) apart in a grid formation. If you prefer, you could make rows 20in (50 cm) apart and plant potatoes around 14in (35 cm) apart within the row. Water them in, unless your soil is already nice and moist.

Once the shoots push through the soil, keep a beady eye on the weather forecast. If a frost threatens, either add a couple of layers of horticultural fleece, or just carefully draw up the soil around the foliage to keep it temporarily covered – they’ll soon push through again. You can expect to be harvesting your spuds as soon as early summer, if you’re lucky!

Sow Hardy Peas

Like those first salad potatoes, peas – fresh from the pod – are a league apart from frozen peas bought at the supermarket. There’s something reassuringly tactile about shelling your own just-picked peas. It’s the epitome of summer, and the starting point to a truly special supper!

Climbing varieties of pea are very vigorous, so once planted against their supports they’ll quickly zoom skywards, especially once the weather begins to warm up. You can expect to pick the first pods from early summer.

Hardy peas may be sown from early spring, and the surest way to do that is to sow into plug trays to keep them safe from mice and (crucially for me!) pigeons. Drop in two seeds per plug of multi-purpose potting mix. There’s no need to thin them once they germinate - they can just be grown on as a pair, ready to plant together in another few weeks about 4in (10 cm) apart.

Peas like to explore as they climb, so a netting trellis support is perfect for them to cling on to. Whatever type of support you use, make sure the uprights are very securely thrust into the ground so they don’t wobble about and get overwhelmed by any unruly gusts of wind.

Start Onions From Sets

Onions are best sown from seed slightly earlier in the year, although you may just about still have time, depending on where you live. If you’ve missed the boat, though, there is another option: onion sets.

Sets are just immature bulbs, primed and ready to send out new roots and grow away again the moment they touch the ground. They can sometimes bolt, or flower prematurely, resulting in little in the way of a useable bulb, but one way to reduce the risk of this is to sow towards the end of the month – around the equinox is ideal in my climate (equivalent to US hardiness zone 8). There’s much less chance of really cold nights from that point, which means that onions are less likely to be tricked into thinking they’ve gone through another winter, which would prompt them to flower.

Plant your sets about 6in (15 cm) apart to give enough space for good airflow between each onion as it grows. Onions are sun seekers, so give them sunny spot to ensure nice big bulbs, and keep the soil moist with regular watering in dry weather. Because onions have such narrow leaves, take the time to carefully pull out any weeds as they appear to remove any competition. To avoid damaging the delicate and shallow roots, I’d suggest removing weeds by hand rather than hoeing.

Position each set so that just the very tip of each one is only just poking out of the soil. Within as little as a week or two, you’ll see them sprouting, which means the whistle has been blown for the race to those bombastic bulbs!

Watch out for mildew, a fungal disease that turns leaves yellow from the tip downwards. It’s especially a problem in cooler, wetter climates. Good airflow can help, which is why proper spacing is so important. If you’ve found this to be an issue, seek out mildew-resistant varieties such as Frontier, Hylander, Powell, Redlander, Santero, Santo, or Toughball.

Get a Head Start on Kooky Kohlrabi!

And now for that weird crop I promised you: kohlrabi! It might be a little unconventional-looking – a bit like a baby alien head! – but I reckon it’s more handsome than weird.

Kohlrabi is a brassica, related to cabbages, broccoli, kale and so on (which are all good to sow right now too by the way), except kohlrabi has been bred to give a swollen edible stem. You’ll be hard pressed to find it in the supermarket, so growing it is usually the only way you’ll get to savour its mild, slightly sweet, yet peppery taste. It’s delicious raw, shaved into salads to give a juicy, crisp-crunchy tang, and it’s almost achingly good for us, packed full of the potent antioxidant sulforaphane.

You could sow kohlrabi seeds direct into soil raked to a fine texture, but I find it easier just to sow into plug trays. Plant two seeds per plug, then if both seedlings pop up, remove the weakest to leave just one in each.

Kohlrabi can be sown throughout the spring, but by sowing early like this there’s a good chance we can get them through to harvest before both those pesky flea beetles and cabbage white butterflies turn up. Think of it as a sort of stealth crop!

Once your seedlings have grown on a bit – maybe in a month’s time – they can be planted outside into their final growing positions about a foot (30 cm) apart each way. Keep them well watered, and harvest promptly up to about tennis ball size before those swollen stems turn woody.

If you haven’t done so yet, please check out the free, no-obligation trial of our Garden Planner. You don’t need to share any payment details to get started, and you’ll be able to try out all its powerful features including companion planting, crop rotation, and its brand-new, incredibly useful Seed Inventory as part of that. This is the perfect time of year to get planning your garden!

Plants Related to this Article

Tomato (Cherry) Grow Guide

Potatoes (Early) Grow Guide

Kohlrabi Grow Guide