Starting Cucumbers and Tomatoes Indoors: Get a Head Start on Summer

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Right. Cucumbers and tomatoes. The big indoor crops. Now, these are the ones that get everyone excited because let’s be honest, nothing beats a home-grown tomato. Absolutely nothing. Those watery things from the supermarket are a completely different species compared to a proper tomato you’ve grown yourself, still warm from the sun. And cucumbers — crisp, fresh, none of that plasticky taste you get from the shop. So let’s get them started indoors and give them the head start they need.

I’ll be upfront with you though — tomatoes and me have had a complicated relationship. I could never grow them in pots properly. Like, I’d put them in the quad grows, and the results were just… all right. Nothing special. Chilies in the quads? Brilliant. Tomatoes? Meh. So this year I’m stripping it back to basics. Bigger pots, better compost, and I’m using that horse bedding as mulch around the base to keep the moisture in. That’s the plan anyway. We’ll see.

Starting Tomatoes from Seed

Tomato seeds want warmth to germinate. We’re talking 18-25°C, so a warm windowsill, a heated propagator, or even the top of your fridge works. Sow them in small pots or seed trays, about 1cm deep, and keep the compost moist. They usually pop up within a week or two.

Once they’ve got their first true leaves — not the little seed leaves, the proper ones — pot them on into individual pots. I use 9cm pots at this stage. Handle them by the leaves, not the stem, because if you snap the stem it’s game over. The leaves can regenerate, the stem can’t.

Now, variety choice. Maris Piper might be Jamie Oliver’s best potato, but for tomatoes you’ve got to think about what you’re going to do with them. Cherry tomatoes are great for beginners — Gardener’s Delight, Sungold, Sweet Million. They’re reliable and you get loads of them. For bigger ones, Moneymaker is a classic, or Ailsa Craig if you want something really tasty.

Cucumbers — The Diva of the Greenhouse

Cucumbers are a bit more fussy than tomatoes, mind you. They want it warmer, they don’t like cold draughts, and they’re thirstier than a camel in a desert. But get the conditions right and they’ll reward you with ridiculous amounts of cucumbers. More than you can eat, honestly.

Start them in individual pots — cucurbits don’t love having their roots disturbed, so I sow them one seed per pot and avoid pricking out altogether. Push the seed in on its side, about 2cm deep. Cover, water, and keep them warm. They germinate fast when it’s warm enough — three to five days sometimes.

Once they’re up and growing, keep them on the warmest, brightest windowsill you’ve got. Or in the greenhouse if it’s warm enough. Mine goes absolutely mental in the greenhouse — “cooking on gas,” as I always say. The heat in there on a sunny day is unbelievable.

The Greenhouse Setup

If you’ve got a greenhouse, you’re laughing. Tomatoes and cucumbers in a greenhouse will outperform outdoor ones every single time in the UK. The extra warmth extends your season by weeks at both ends. You can plant out earlier and keep harvesting later.

I’m getting a new greenhouse sorted at the allotment — had to get replacement glass, toughened 4mm stuff. Me and silicon aren’t exactly best mates, but we’ll get there. Allan helped me source it from a company near the garden centre. The plan is to get it up in time for next season, face it the right way for maximum sun, and finally have a proper home for the tomatoes.

If you haven’t got a greenhouse, don’t worry. A south-facing wall, a cold frame, or even a sunny patio with pots will work. You just need to wait a bit longer before planting out and maybe protect them on cold nights.

Feeding and Watering

Once they’re planted out, tomatoes need regular feeding. When the first truss of flowers appears, start feeding with a tomato feed every week. I use whatever’s on offer at the garden centre. They all do the same thing — give the plant the potassium it needs to produce fruit. Don’t bother with expensive stuff. A cheap tomato feed works just as well.

Watering is key. Consistent moisture. Not too much, not too little. Irregular watering causes blossom end rot — that’s when the bottom of the tomato goes black and mushy. Devastating when it happens. The trick is to water at the same time every day. I water mine in the morning before it gets too hot.

Cucumbers want even more water than tomatoes. They’re about 95% water, so it makes sense. In the greenhouse on a hot day, you might need to water them twice. Mulching around the base with straw or that horse bedding I mentioned earlier helps massively — keeps the moisture in and stops the soil drying out so fast.

Common Mistakes I’ve Made

Where do I start? I’ve overwatered. I’ve underwatered. I’ve forgotten to remove side shoots from cordon tomatoes and ended up with a green jungle that produced about three tomatoes. I’ve tried to ripen fruit in a greenhouse that doesn’t get enough sun — me yard one is in shade for half the day, which is useless for ripening.

The biggest lesson? Don’t try to grow too many. Seriously. Six tomato plants will give a family of four more tomatoes than they can eat. I used to cram in twelve plants and none of them did well because they were all competing. Now I grow fewer plants but give them more space, more light, and more attention. Better results every time. Plant later, sow less. It applies to everything.

Look after yourselves. Take good care. 🌱