How to Grow Tomatoes - 10 Simple Rules

I write this primarily for several friends who have taken, or are about to take, spare tomato plants off my hands and who have asked for full instructions on how to look after them, but hopefully lots more people will find it useful too! For some it can be daunting growing things for the first time, or growing things you've never grown before, but really most plants' needs are very simple and as long as you know what those needs are, it doesn't have to be daunting at all!

Here are the needs of a tomato plant:

1. Warmth. Keep above 5C, preferably 10C, and only plant outside when the risk of frost has passed.
2. Sun. Always keep them in a sunny location. 
3. Good compost, which provides nutrients and retains moisture.
4. Support (except with tumbling types), to help the plant bear the weight of its fruit.
5. Dryness. Avoid getting the leaves wet where possible. A greenhouse is ideal but not by any means vital. Good pruning promotes air circulation which will help plants to dry quickly.
6. Pollination. Outdoors, bees will do this for you. Indoors, just shake the flowers!
7. Regular watering. Fruits need lots of water to swell, and irregular watering can cause fruit to split, so water the same amount every day as far as possible.
8. Food. While not vital, applying tomato feed once a week can get you a better crop.
9. Pruning. Pinch out extra shoots or 'suckers' from leaf joints to provide good air circulation and focus energy on fruit-production.
10. Protection from fungal infection. Remove any leaves that drag on the soil and any that show signs of disease. Consider using a fungicidal spray (bought or homemade - see below) to protect your plants during humid weather.

That's really all you need to know, but if you want more, here's the long version...


Sowing Tomatoes

Tomato seeds need heat to germinate and must be sown indoors, anytime from January to early April, and kept above 10C. Fill small pots (3" is ideal) with clean, new compost, firm it down gently and water it. Then use your fingertip or a pencil to poke a shallow hole, 3-5mm deep, in the middle of the soil in each pot. Drop two seeds into each hole and add a pinch of fine compost or vermiculite to fill it in, or simply 'pinch' the hole carefully closed. Place in a propagator or cover the pots with plastic wrap to retain moisture until the seedlings have appeared - or simply water very lightly with a spray bottle twice a day to stop the surface drying out.

Seedlings will usually appear within a week, and definitely within two. Remove the plastic covering as soon as you see them and keep seedlings in a sunny place - if they don't have enough light they will reach for more and grow very tall and 'leggy' very quickly, which will give them weak stems unable to support the plants properly. When the temperature is above 10C during the day, it's ideal to put them outside in full sun, but keep them out of strong winds and heavy rain/hail showers until they're bigger, and don't forget to bring them in again at night! If two seeds have germinated in the same pot, wait until they grow their first true leaves then select the stronger one and pinch the weaker one off at soil level.

If you prefer, you can sow into smaller pots, cells, or a seed tray. When the plants are big enough to handle, though, they should be carefully transplanted to larger individual pots.

Ready to plant out...

Planting Out

Tomatoes don't like cold temperatures and frost will kill them, so keep them protected from cold but in plenty of sun until the risk of frost has passed. If you will be growing them outdoors, check the last-frost date in your area and wait until then before planting out. In my area, it's early- to mid-May. But if you plant them outside and then a late frost is forecast, don't panic - covering your plants gently with newspaper, a sheet or a towel (don't squash them!) is often enough to protect them. If you're going to be growing them in a heated greenhouse or conservatory, you will be able to plant them out much earlier - as soon as night temperatures in it are reliably around 10C. Plants should be at least 6"/15cm tall before planting out, and you should 'harden them off' for 7-10 days by putting them outside during the day, to gradually get them used to outdoor temperatures and winds.

Like virtually all fruiting crops, tomatoes need lots of sun, so pick a spot for them that gets at least six to eight hours of direct sun a day - the more the better.

I think the easiest way to grow tomatoes is in a growbag, and you can now get growbags specially formulated for growing veg in, which I highly recommend. Roll the growbag on its side to break up the compacted soil, put it in position, then cut holes for your plants and scoop the soil aside to make holes big enough for the tomato plants. Water your tomatoes before planting out to reduce stress, and try not to expose the roots to direct sunlight or leave them sitting around out of a pot for any longer than necessary. Pop them in the holes in the growbag, level and firm the soil around them, and water the growbag well.

See all the little hairs around the bottom of the tomato plant stem? If you plant it deeper than it was before, those hairs will grow into extra roots and give you an even stronger plant!

Tomatoes can also, of course, be grown in pots or in the soil in your garden - just make sure you use good compost to provide nutrients and retain moisture. Plant them around 12"/30cm apart.

Stick a cane in the ground as close as you can to each stem without damaging the roots. This is tricky in growbags as they are not very deep - try sticking the cane right through the bag into the ground, or check out the various types of cane support you can buy or make. As the plant grows taller, tie it loosely to the cane every 9-12" to support the weight of all that lovely fruit you're going to get! Another way to do it is to fix a stake or post every two or three plants, and tie strings between them that pass both sides of the stems. Look up 'Florida weave' for examples of this.


Caring For Your Plants

Uneven watering can cause fruit to split, so try to water regularly. Even in heavy rain, growbags and pots don't tend to catch that much water, so while your plants are fruiting, water them the same amount every day or two, whatever the weather. Growbags can be tricky to water - it sometimes just runs off. I remedy this by cutting the bottoms off plastic bottles and burying them neck down in the soil next to the plants - watering into these takes water straight to the roots where it's most needed, and allows the water to soak in gradually rather than running away.

  Splitting caused by irregular watering.

Many gardeners apply a tomato feed every week or two starting from when the first flowers open - this will encourage maximum fruiting. Using growbags already formulated for tomato-growing, I find this unnecessary, but who knows, maybe I'm missing out on an even bigger crop! Seaweed extract treatments are also particularly good for tomatoes.

Most tomato plants need pruning to keep plants focussed on fruit-production. (If your tomatoes are 'determinate', bush or tumbling varieties, they do not need pruning, but the ones I have given my friends are 'indeterminate' which means the plants will just branch out more and more, endlessly, so pruning is important.) Don't panic - it's very easy! What you're aiming for is a straight upright stem with only leaves, flower trusses and fruit trusses growing from it, like this:

When you see an extra shoot, or 'sucker', forming at the base of a leaf, like this...

Just pinch it off, like this...

If you do this carefully and don't damage the hairs on the stem, you can plant these prunings in pots of compost and grow whole new plants! (They may look like they're dying to start with, but they'll bounce back with a little TLC.) If you don't remove these extra shoots, your plant will end up with lots of extra branches and lots of extra leaf growth, will become tangled and unmanageable and will make your plant more susceptible to fungal infection...

Tomatoes are prone to a fungal disease called tomato blight, especially when grown outdoors, which starts as spots on the leaves, spreads to the stems and will eventually turn the fruit black. Rain carries airborne blight spores down to the leaves and soil, and the infection sets in during hot, humid spells. To decrease the chances of disease, try not to get the leaves wet when watering, and keep plants pruned so that they are well-ventilated and dry quickly after rain. If the lower leaves hang down to touch the soil, snip them off, and if any leaves turn yellow or develop brown or black patches, remove them too. Don't spread infection by touching infected parts and then touching non-infected parts, or by letting an infected plant touch others. If you think your plants may be infected, or during a period of more than 48 hours of hot, humid weather, spray your plants with a 1:1 milk and water solution, or 3 tbsps bicarbonate of soda and 1 tsp washing-up liquid to a gallon of water, to raise the alkalinity of the leaf surfaces and make it harder for fungi to take hold - or of course you could use a chemical fungicide. You can do this every week and after rain to prevent blight, or more often to slow its progess once infected. Spray in the evening or early morning, and always out of direct sunlight. Blightwatch.co.uk offers a free service to warn you when the weather conditions are just right for blight to hit your postcode so you can take precautions - give it a try!

 When black patches reach your plants' stems, you know it's blight.

If your indoor tomatoes are attacked by whitefly, grow basil around them - the flies hate it. Outdoor tomatoes don't tend to suffer much pest damage, but keep an eye out for slugs, snails, caterpillars and aphids just in case. Encouraging ladybirds in your garden is the most natural way to deal with aphids, but squishing them by hand is also very effective. Slugs, snails and caterpillars are best dealt with manually too - you'll need to go out after dark with a torch to catch slugs and snails - or you could use beer traps or organic slug pellets.

If you're growing tomatoes indoors, you will have to either open doors and windows wide during warm days to let pollinating insects in, or pollinate by hand. This is really easy - tomatoes are self pollinating, meaning they only need their own pollen to reach their own stigma, so it can be done simply by shaking flower trusses, flicking or blowing into the flowers, or by vibrating the flowers with the back of an electric toothbrush or an electric razor with the blade removed to mimic a buzzing bee! Do this every few days when flowers are opening. If you're growing outdoors, bees and other insects will do this for you. If you don't have many bees in your garden, you can attract them by growing more flowers! Here is a list of flowers which help to attract bees. Marigolds, poached-egg plant, poppies, borage, sunflowers and cornflowers are particularly good and easy to grow.


Harvesting

Harvest your tomatoes when they're fully red (if, that is, you're growing a red variety!), but try not to let any overripen on the plant, which may stall further fruiting. Keep your harvested tomatoes at room temperature - the fridge ruins their sweetness!

If you keep harvesting and pruning your plants, they'll keep producing right up until the first frosts around October or November. Enjoy them, and good luck!

And why not try saving your own seeds for more free tomato plants next year? Just click here and follow the instructions!