Changing climate leads to outdoor crops too
Growing tomatoes under glass used to be a necessity here in NE England. Our summers tended to be dull and cool, so they went into the conservatory and greenhouse, all indeterminate, or cordon varieties, which need support. The conservatory is narrow and tall, so I need tomatoes that match its dimensions.
However, things have changed. For the last two years, I’ve managed to get reasonable crops for plants outdoors (Tumbling Tom Red and Rosella). I also no longer grow cordon varieties in the conservatory, as I had to climb up ladders to harvest them. Now, I use bush varieties, which take up more space widthways but are easier to pick and don’t need tying in and side-shooting.
Seedlings usually appear in 5-14 days (see below). Once they are through, give as much light as possible (I use a grow light) and grow on in cooler conditions.
When the first true leaves appear, prick out into individual pots (my favourite yoghurt/rice cartons). Plant into large pots, grow bags or greenhouse beds from April to May. Provide support, pinching out side shoots regularly. Pinch out the main growing tip after 5-6 trusses have set. Here’s why tomatoes don’t set fruit.
Varieties I’ve grown over the past few years
SUNCHOCOLA F1: Sweet, with a distinctive red/brown colour.
RED/YELLOW CURRANT: Grafted plants, a trial from Big Allotment Challenge Winner Rob Smith’s range from Dobies. He said: “It’s a different species from your common garden tomato, and it’s hardly changed since it was found growing wild on a Peruvian beach in 1707. The plants are very disease-resistant and can tolerate cooler temperatures. Each tiny tomato is crisp, and has a really intense, sweet/tart flavour.” These did grow well outdoors, and the flavour was great.
ORANGE PARUCHE F1: The high sugar content gives the fruit a superb flavour. A challenge to Sungold.
PINK CHARMER F1: Very vigorous, distinctive pink fruits, good flavour.
GREEN ZEBRA: ‘Modern heirloom’ type with dark green and yellow stripes. Newer variations blush reddish instead of yellow when ripe. It is more tart than regular tomatoes, and it is an early cultivar. Produces bigger fruit than a cherry at 3oz (75g). The ‘Marmite’ tomato – my family hated it, so naturally, it produced a huge crop.
CRIMSON CRUSH F1: The world’s first fully blight-resistant tomato, with large, round tomatoes (up to 8oz/200g). It’s bred for outdoors, but can be grown indoors too.
SUNCHERRY SMILE F1: Masses of wonderfully sweet red cherry fruits with very shiny skins.
A note: The F1 varieties cost a lot to produce, so are expensive, and you’ll only get eight-15 seeds per packet. However, Green Zebra is not an F1 variety, so it is much cheaper and has an average of 75 seeds per packet.
Potted guide: Growing tomatoes under glass
- SOWING TIME: January-March (only sow very early if you use grow lights). Sow 0.5cm (¼”) deep, thinly in a seed tray and cover with Vermiculite or Perlite, 15-20°C (60-68°F).
- HARVESTING TIME: June-November.
- ASPECT AND SOIL: Full sun, rich, well-drained.
- HARDINESS: Tender.
- DIFFICULTY: Moderate.
- RECOMMENDED VARIETIES: Cherries: Rosella, Orange Paruche F1, Pink Charmer F1, Suncherry F1, Black Opal, Pink Baby Plum F1, Sungold F1. Beefsteak: Brandywine (heirloom), Burlesque. Bush/trailing: Tumbling Tom Red, Veranda Red, The Amateur.
Different cultivation methods for growing tomatoes under glass
As well as the usual grow bag or large pots, I have tried out some different methods of cultivation – with varying levels of success.
The problems
- Lack of space: my conservatory is 30ft x 5ft – I have to shuffle through sideways when it’s full.
- Light: The windowsill plants block the light to the staging, leading to a poorer crop and leggier plants.
- The climate: Most of my crop is grown under glass, as summers can be variable.
The solutions
Aspirin: Spraying a dilute solution of aspirin onto tomato plants (half a soluble tablet per litre of water) causes their sugar content to increase by 150 per cent and boosts Vitamin C by 50 per cent with a single spray.
Aspirin is a close chemical copy of the plant stress hormone, salicylic acid, which turns on the genes that regulate their defence systems, so more sugars are redirected to the developing fruit. The flavour of the tomatoes was exceptionally good – I’m happy with the result.
Growing tomatoes under glass – Ring culture pot method
Growing in ring culture pots: Pure necessity here. The conservatory was packed with half-hardy plants in early May, so there was no chance of getting grow bags or the bigger pots in. I didn’t want to pot them on twice, especially as the first truss was forming. I took my ring culture pots and started planting them up on a tile, then sliding them off it onto a gravel tray when finished.
It meant the tomatoes could grow on without disturbance, in good light and warmth, and eventually moved into the greenhouse or permanent positions in the conservatory. Read more about growing tomatoes in grow bags.
One-truss growing
I saw James Wong at The Edible Garden Show talking about this – an answer to my space prayers. You stop the plants two or three leaves after the first truss has formed. The theory is that you get bigger, sweeter tomatoes, and the drop in yield is offset because you can cram more plants in. In the space, I would have had three light-blocking large grow bags with 17 Gardener’s Delight plants in 18-19cm pots, which would have been wasted. The pot size is a guess, as you’re supposed to grow them in a bed.
So, how did it go? I got a reasonable crop out of 17 plants that would have been wasted, but it would have been better to use Orange Paruche or Rosella, which set bigger trusses. These tomatoes didn’t block the light, leading to a bigger crop from the plants on the staging, and were finished by July, leaving an airy, uncramped conservatory for the first time. Recommended.
Growing tomatoes under glass – Best performers
I grew five varieties – all cherries – here they are, in descending order.
1. Orange Paruche F1: top for quantity, taste, and length of the season. Better taste by far than Sungold (yes, really). Perfect balance of sweetness and acidity in a small cherry.
2. Rosella: a dark chocolate colour with green shoulders, this has a superb taste and is a big cropper, with huge trusses. Still producing fruit in the greenhouse in mid-October.
3. Pink Charmer: good taste, bigger fruit than the others and a heavy crop, but a tendency to split. Still a good buy.
4. Black Opal: great colour – unfortunately, it makes the fruit harder to see and pick! Problem with fruits splitting. Flavour not as zingy as the others, but good for an interesting salad.
5. Gardener’s Delight: the old standby comes last for taste, although much better than shop-bought tomatoes, and reliable. Produced much bigger fruit, as expected, in the one-truss trial, but I’d have had a bigger crop growing more Orange Paruche or Rosella in this way.
The early aphid problem and fungus gnats in the grow bags were sorted by increasing the yellow sticky traps, so much better than last year. The Dalefoot Composts mix was excellent in the greenhouse bed, holding water brilliantly, and I didn’t go overboard on the feeding. A must – worth its weight in gold!
