How to grow your own tomatoes. A complete how to guide on growing tomatoes, including what are the best varieties to grow in our climate as well as when and where to grow. Also included is planting and transplanting, crop care, pests and diseases (including tomato blight and aphids), harvesting, and storage.
Tomatoes are one of the most rewarding crops for the home gardener to grow simply because their flavour is so much better than their shop bought cousins. Tomatoes grown for the supermarket shelf have been bred to travel well and look good on the shelves for as long as possible; tickling your taste buds is not their number one priority.
Many commercially produced tomatoes are also grown in soilless environments using an artificial fertilizer solution and are picked before they are ripe; both of these practices result in tomatoes that look nice but don’t taste great. Research has also shown that organic, homegrown tomatoes have a much more complex chemistry than commercially produced fruits. Not only does chemistry equal a greater depth of flavour, it is also likely that homegrown tomatoes are healthier with higher levels of the pigment ‘Lycopene’. Lycopene has been shown to help unclog blocked arteries and is thought to be one of the reasons the Mediterranean diet is so healthy.
The other big bonus with growing your own tomatoes is the amazing variety of size, shape, colour and flavour there is available. A bit like the potato (they are, of course, close relations) there are a huge range of different types for very large ‘beefsteak’ varieties to small and sweet ‘cherry’ fruits. They are fun to grow and give such a great reward that they have to be one of stars of the home vegetable plot.
Tomato Terms Explained
Before we get into the details on how to grow tomatoes I would like to explain some of the terminology you are likely to hear, a little understanding here will be helpful in choosing the right variety for your garden.
Most Popular Fruit Types
Standard - Medium sized tomatoes of the size you are likely to see in the shops. Smooth, round tomatoes usually red or yellow skinned. They are good all purpose tomatoes.
Beefsteak - Large mediterranean style tomatoes excellent for sandwiches and salads (think tomatoes with mozzarella). Be aware large tomatoes need a long season to ripen so not suitable for growing outside in cooler climates. Beefsteak are well worth growing if you have a polytunnel or greenhouse for their interesting and unusual variations and good flavour.
Plum - The traditional Italian for canning and making pasta sauce. Not the best for fresh eating flavour but cook and freeze well.
Cherry - Small, round fruits usually with excellent flavour. Red and yellow skinned varieties including the fantastic ‘Sungold’ which you absolutely must grow.
Indeterminate or cordon varieties - The typical tall type plant most people will be familiar with. They are usually grown up twine or bamboo supports and consist of a single long stem. Cordon varieties produce side shoots which will grow into large lateral branches; they will need to be removed as they appear to keep the required growth habit. Allowing the lateral branches to spread will result in a congested plant and a lower yield of ripe fruit.
Determinate or bush varieties - Suitable for growing in containers, hanging baskets or anywhere where space is at a premium. Bush varieties don’t grow with a central stem and have a low growing, sprawling habit making them useful for growing under cloches or mini polytunnels.
Removing side shoots is not necessary as the bush is ‘self stopping’ usually achieving a 2-3 foot spread. Fruits tend to be smaller and ripen relatively early.
Dwarf varieties - Very small and compact plants growing no more than 8 inches high. Ideal for container growing. Dwarf varieties are great if you have small covered raised bed like a Vegtrug manger planter as they won’t outgrow the cover.
Where to Grow
Tomatoes are sub-tropical plants and therefore require a position in full sun. This is especially important in most areas of the UK and Ireland where sunlight and warmth are at a premium even in mid-summer. A position against a wall or fence will give a better chance of success as long as they can receive sufficient water; avoid hedges as the soil will be too dry. Tomato plants also grow very well in raised beds, they appreciate the soil conditions which provide moisture without water-logging.
In cooler parts of the UK and Ireland (that's most of Ireland...) tomatoes are better grown undercover in a polytunnel or greenhouse. In poor Summers outdoor tomatoes can fail to ripen (especially larger varieties) or fail altogether.
Site and Soil
Tomatoes require a very fertile soil. Remember a healthy plant may be up to 2 metres tall and produce hundreds of fruit while taking up a relatively small space (a cabbage takes up more room and only produces a single head!). Prepare your beds by adding plenty of well rotted manure at planting time, as much as a full wheelbarrow every 3 square meters.
Tomatoes can also be grown in pots and growbags but due to the restricted root space you will need a more intensive feeding regime. Make sure pots hold at least 40 litres and only plant 2 plants in a growbag, these conditions are not ideal but may be the only option in a small city garden or if growing on a balcony. Use a the best compost you can and feed with a generous amount of seaweed and poultry manure pellets when planting out, supplementary liquid feed with an organic seaweed feed.
Tomatoes respond well to inoculation by mycorrhizal fungi which build a symbiotic relationship (benefits for both species) with the plant. The fungi form a network of hyphae which transport water and minerals the tomato plant in return for sugars produced by the roots. Mycorrhizal fungi are available as a powder to coat seedlings when planting out or a coconut fibre 'biscuit' which is placed in the bottom of the planting hole.
When to Grow
Sow seed indoors in late February to mid March using a heated propagator or a warm, South facing windowsill. The temperature of the compost should be approx 22 degrees celsius for the seeds to germinate; young plants will also need to be kept warm until early Summer when the soil temperature is above at least 10 degrees.
Tomatoes can be sown in seed trays and pricked out to larger pots but I prefer to sow in modular trays and pot on to a larger 10cm pot after the third leaf has formed. Seeds should be sown 2cm or 3/4 inch deep in a low nutrient seed compost and potted on to a richer potting compost.
We need to achieve a balance with our seedlings at this point as we are keeping them artificially warm at a time of year when light levels are not really sufficient. Too much heat and not enough light will result in tall and weak seedlings (because they grow fast assuming if there's heat there must be more light) so we need to reduce heat to a minimum (10 degrees) and place the plants in as bright a position as possible. If you are growing indoors on a windowsill you may need to provide extra light using a growlamp.
Plants grown in pots need to be spaced out when their leaves touch each other to avoid overcrowding and plants becoming elongated and 'leggy'; the best tomato seedlings are short and stubby rather than tall and thin. Compost should also be kept moist and should never be allowed to dry out.
Where tomato seedlings have been started in pots or containers, they should be transplanted into their final positions when they are approx 15cm (6in) high before the roots become restricted by the pot or 'potbound'.
Where tomato plants have been grown under cover and you intend to plant outdoors, remember to harden them off for a week or two before planting them in their final outside positions. Hardening off means getting them gradually used to outside temperatures by leaving them outside on fine days and bringing them in at night. You leave them out for progressively longer until they can be left out at night provided all risk of frost has passed. This is especially important in the UK because May and June can often be cool and windy.
Dig a hole for each plant (45cm / 18in apart) in the bed to about 5cm / 2in deeper than the pot. If you are growing indeterminate or cordon varieties you will need to provide support. You can do this by burying a length of twine under the root ball when planting and tying the other end to a support above the plant, this is easy in a polytunnel where you can tie on to crop support bars. For outdoor planting there are a wide range of tomato supports available.
Ease the tomato plant out of the pot, keeping the root ball undisturbed as far as possible. Place it in the hole and fill around the plant with soil. The soil should be a 5cm / 2in higher than it was in the pot. Planting tomato plants deeper in the soil than in the pot will encourage the formation of additional roots. Water well if conditions are at all dry.
Transplanting Leggy Plants
If your tomatoes are a bit leggy and elongated you can partially remedy this by planting deeper than normal and burying up to 2/3 of the plant including the lower sets of leaves. Tomato stems have the ability to grow roots from buried stems you can build a deeper and more extensive root system this way.
Tomato Crop Care
If you are growing cordon varieties (and chances are you are) you will need to pinch out any side shoots which form to prevent energy sapping lateral branches growing. The side shoot will appear at the point where a leaf branch meets the main stem; they can be nipped off with your finger nail when small but will need to be cut with a sharp knife or secateurs if allowed to grow larger. New tomato growers can find it difficult to spot these shoots and can confuse then with the start of a new fruit truss (you don't want to remove them!), if you are unsure leave them for a few days, if the shoot starts to produce leaves, off with its head! Remember the side shoot is always in the space between the branch and the main stem, once you get used to spotting them you will wonder why you ever found it difficult.
If fruit is slow to set in early Summer tap the plant support around midday to encourage the spread of pollen.
If you are growing in a greenhouse or polytunnel keep well ventilated especially on hot days to prevent the build up of pests and disease.
Stopping is the practice of removing the main growing tip to prevent further fruit truss formation and to encourage existing fruits to ripen. If growing outdoors this is normally done when four or five fruit trusses have set but in cold years it is better to stop when three trussed are present. For polytunnel growing it seven or eight trusses can be expected but in more northerly gardens or in a cold year limit the plant to five or six.
To stop plants cut off the top of the main stem, continue to remove side shoots as normal.
Water well when planting out and then lightly until the fruit starts to set. Once fruit is setting water well with 12 litres (2 gallons) per plant at least on a weekly basis. Letting the soil dry out between waterings has been shown to improve flavour but be careful with this as drought conditions followed by heavy watering can cause a growth spurt which results in split fruit. Watering will take a little practice but keeping plants slightly on the dry side will intensify flavour.
I have had good success with burying perforated plastic bottles in the soil between plans which act as a watering reservoir. Cut the bottom of a 2.5 litre bottle and make numerous small perforations in the sides. Bury the bottle upside down with the lid on and fill when you are watering, the water will seep through the bottle walls and deep water the soil.
Once the fruit has set feed weekly with a liquid comfrey feed or a seaweed tonic formulated for tomatoes. It is worth remembering that tomatoes have two types of root, deep roots for transporting water to the plant and shallow roots which absorb nutrients. When feeding tomatoes you are better to drench the soil around the plant with a feed solution rather than using the bottle reservoir above.
Few pests or diseases trouble outdoor tomatoes, failure is usually caused by wet or cold weather. Leaves turning mottled, purple veined or reddish under leaves is usually caused by nutrient deficiency caused by low temperatures. Roots are unable to absorb nutrients when the temperature is cold. This can also be the cause of blossom end rot.
Fruit Splitting - A common problem with tomatoes caused by irregular watering with some varieties more prone to this than others. A more regular watering regime should solve this problem.
Calcium Deficiency & Blossom End Rot - Blossom end rot is a dark and often rotting area around the base of tomato fruits and is caused by a shortage of calcium. The problem may be under watering as calcium uptake is slowed in drought conditions. Again, a more regular watering regime should solve this problem.
Magnesium Deficiency - The symptoms are yellowing of the leaves while the lead veins remain green, older leaves are affected first. Remedy the problem by using ground magnesium limestone.
Pests and Diseases
Whitefly are the most likely pest to affect your tomatoes. The adult flies (they look like tiny moths) lay eggs on the underside of leaves. The growing eggs feed on the leaves, leaving a sticky secretion which attracts other diseases. As soon as you see the eggs, try spraying with water to wash them off and remove others by hand.
There is an excellent biological control available, a tiny wasp which feeds on whitefly. 'Encarsia Formosa' eggs are available mail order and should be used at the first signs of attack, if the plants have already become infested it is too late.
This is caused by the fungus Phytophthora infestans which is also the cause of potato blight. The signs are brown marks on the leaves which quickly increase in size. If left, any developing fruit starts to turn brown and rots.
Click here for more details on Tomato blight.
Aphids (Blackfly and Greenfly)
Planting Marigolds really does attract beneficial insects such as ladybirds and hoverflies and these love to eat blackfly. Spraying the plants with water also works - it simply knocks the blackfly off the plant. Where neither of these methods work, its down to the garden centre for a chemical spray - most work well.
Click here for more details on Aphids.
There are many varieties of mosaic virus which can affect tomatoes but they can all be identified by leaves which turn yellow, then bronze and become distorted. This is a very infectious virus which can be transmitted by humans from plant to plant.
Pick as soon as the fruits are ripe (colour and size will identify this) for the best flavour - eat as soon as possible. This also encourages the production of more fruit. As soon as a frost threatens in October/November, harvest all the fruit immediately and ripen them on a window sill. With upright varieties, it is possible to gently flatten the plants and cover with horticultural fleece to protect them from frost.
Wash and dry your tomatoes before storing. Unless you're planning to store your tomatoes for over a week, a windowsill, counter-top or bowl works fine. If you know you won't use them in the next few days, then lower temperatures will help preserve the fruit. Storing in a fridge is not recommended, as the cooler temperatures can reduce flavour and cause mushiness. Your fresh-picked tomatoes should last longer on the kitchen counter than supermarket-bought ones, which are probably a few days old when you get them.