Tomatoes

The flavour of home grown tomatoes is unbeatable, no shop bought tomato can ever compete with a thin skinned variety picked fresh and sun warm from the vine.

The most critical thing with growing tomatoes is to keep them fed and watered properly. More than any other crop, they need regular watering and feeding to produce successfully. A great way to improve the moisture/air holding capacity of potting soil is to add Perlite.

Perlite holds both moisture and air, so it is ideal for keeping roots healthy and plants growing at a consistent rate.

Every time water only is applied to the roots from above, nutrients are washed away from the top few inches of soil – where most of the fine, nutrient absorbing roots live!

This is one reason for the success of the Grow Pot and “Ring Culture”.

Plants are fed/watered in the inner ring and watered in the outer ring. This avoids the problem of water only, removing nutrients from around the fine roots close to the stem base.

Using Grow Pots is a great way to optimize a grow bag.

It’s very easy to overfeed tomato plants – especially when they are young seedlings. The problem with feeding young plants is that their roots are very sensitive and may be damaged if fed a solution of feed that is too strong – such as the same strength that a fruiting adult plant would have.

If you use good compost (already containing food) there is very little need to feed until the plant is beginning to fruit – assuming that it has been potted-on with new compost. After about four weeks in a small pot the nutrients in the soil will have been used-up, so extra feeding may be necessary if the plant is not potted into a bigger pot with more potting compost.

Tomato plants that are fed “little and often” generally do better than those that are fed once a fortnight. This is especially true when plants reach their reproductive stage – flowering and fruiting.

Tomato plants have two stages of growth:

• The growth or vegetative stage – before flowering
• The reproductive stage – flowering and fruiting

Before Flowering

This is when plants need a balance of nutrients and are normally fed with a general fertiliser. These feeds contain nitrogen, phosphorus and potassium (NPK) in more or less equal amounts, plus other nutrients and trace elements.

Before feeding with a fertiliser, take into account the compost that your plants were potted into.

There are already plenty of nutrients in new, multi-purpose and grow bag soil, so feeding is not really needed until the food runs out – usually around three weeks in a small pot and five or six weeks in a grow bag, large pot or container.

After Flowering

This is when plants require tomato food and are fed on a weekly basis.

Tomato fertiliser also contains greater amounts of phosphorus and potassium for flower and fruit growth. However, plants still require a small amount of a wide range of minerals, including nitrogen, in order to develop more trusses and top growth.

Liquid Seaweed Extract is an excellent organic supplement and can be used as a foliar spray to encourage healthy and vigorous growth.

What are fertilisers?

Fertilisers contain concentrated sources of plant nutrients in chemical or organic form. Most contain major plant nutrients, which plants need in relatively large amounts. Some also contain trace elements, which plants only need in tiny amounts.

Most fertilisers are based on the three major plant nutrients:

• Nitrogen (N): For green leafy growth
• Phosphorus (P): For healthy root and shoot growth
• Potassium (K): For flowering, fruiting and general hardiness

All fertilisers should quote their N:P:K ratio on the product packaging. For example, a ratio of 20:20:20 indicates a balanced fertiliser, but a ratio of 10:12:24 would indicate a high potassium fertiliser.

Product choice

There are two main types of fertilisers: inorganic (man-made) and organic (derived from plant or animal).

Inorganic fertilisers: These are synthetic, artificial forms of plant nutrients or naturally occurring mined minerals. Inorganic fertilisers are usually more concentrated and faster acting than organic fertilisers. Examples of inorganic fertilisers include: Growmore, Miracle-Gro, Phostrogen, Sulphate of Ammonia, Sulphate of Potash, and Superphosphate and Tomorite

Organic fertilisers: These are derived from plant or animal sources and contain plant nutrients in organic form. Organic products tend to be slower acting, as large organic molecules have to be broken down by soil organisms before the nutrients within them are released for plant use. Examples of organic fertilisers include: seaweed, fish blood & bone, bone meal, poultry manure pellets.

Types of Tomatoes

Cordon or Indeterminate Tomato Varieties

These tend to be the most popular types, usually tied to a cane or string and the side shoots are removed to ensure the plants energy goes into the fruit rather than foliage. When a number of trusses (The plant stalk that bears the flowers and fruit) are set, the plant is stopped to allow the fruit a chance to ripen before the end of the season. 

Bush or Determinate Tomato Varieties

Bush tomatoes differ in that they do not need side shoots removing and are effectively self stopping. The drawback of this is that they take up more room and are not so suitable for growing in pots. They do not generally require much or any support but the fruits are often in contact with the ground, which means more vulnerable to slugs and other pests. They can, in poor years, leave you with more green and under-developed fruits but you can compensate for this if you can get them off to an early start.

Dwarf Bush or ‘Hanging Basket’ Tomatoes

Unlike the standard determinate varieties of tomato, these are smaller plants usually giving cherry tomatoes and are bred to grow in containers such as hanging baskets. My experience is that they can be very successful.

Tomato Fruit Types

As well as plant types there are quite a number of different tomato fruit types. As a home grower, you can find many different – some weird and wonderful – varieties but the main types of fruit are listed below:

• Standard – the ‘normal’ tomato, spherical in shape and around an inch to an inch and a half in diameter.
• Cherry – just a small version of the normal tomato, often marble sized. Often from dwarf bush types.
• Beefsteak – a large version of the normal tomato. Because of their large size, these tomato varieties take longer to mature and ripen so really do not do well except in a greenhouse.
• Plum – the firm fleshed oval shaped fruit you find in Italian canned tomatoes. Tend to have been bred to store well as bottled (or canned) and they freeze well. (See Storing the Surplus)
• Marmande – large irregular shaped tomatoes. Often very tasty.
• Heirloom Tomatoes (Heritage Tomatoes) These are older and often rare varieites prized for their flavour.

Growing Tomatoes in Pots or Grow Bags in the Greenhouse

The advantage of greenhouse growing tomatoes in pots and grow bags is that the compost is fresh each year. This means that it is free from disease build up and pests. Once the season is over, the spent compost from the pots and grow bags can be used as a soil improver on the plot.

What size pot to use for growing tomatoes?

Basically, the larger the pot the better. The minimum size is a 10” (20cm) pot which holds approximately 10 litres of compost.

Grow bags for Tomatoes

The original concept of the grow bag was excellent. They are convenient, neat and effective. Just make some drainage holes in the bag, cut holes on the top and plant through them. The bag effectively stopped evaporation water loss.

The only drawback was watering. One way to solve this was a variant on the old ring-culture growing method. Another solution was grow bag watering pots. These are inserted into the bag and water easily added through them.

Tomato Side Shoot Removal

To channel the plant’s energy into producing fruit rather than foliage we need to remove the side shoots. These always start in the angle between the leaf and stem, above the leaf.

The earlier they are removed, the less energy is wasted. A job to be done at least once a week. They are easy to miss, so whenever you are watering or feeding your tomatoes, keep an eye out for them and remove.

After the plant is stopped, it reacts by producing more side shoots – so watch out. Be careful not to confuse these shoots with a truss. A truss is the stem that carries the flowers, which turn into tomatoes. These grow from the stem but not from the leaf joint.

Rather than cutting these side shoots off, tear them away. It sounds crude but ripping them away results in better formation of scar tissue and is less likely to bleed or allow disease to get in.

Stopping Tomatoes

As the season draws to a close the plant will not have time to set, grow and ripen more fruits and it is time to stop it. This is usually when the plant has set four or five trusses but with some varieties you can get seven or eight.

A lot depends on when you sowed and planted as well as the speed which the plant grows fruit. Tomatoes range from 50 to 80 days to crop from germination.

How to Stop Tomatoes

You just take the leading (main) shoot at the top and pinch or cut it off. This means all the plant’s energy can be diverted into fruit, which will hopefully mature before the end of the season. Be aware the plant will react to being stopped by trying to form new shoots so you need to increase your vigilance when side-shooting.

Tomato Pests and Diseases – What’s Eating / Killing my Plants?

Although tomatoes are very easy to grow and are very rewarding there is a vast number of pests and diseases that can attack your precious crop.  Fortunately for the amateur gardener, most of these are unlikely to cause a problem as most are easily preventable or simple to treat.

Tomato Diseases

For the home grower, there are some very simple things that can be done to prevent disease in tomatoes.

Avoiding Tomato Diseases

As healthy plants are much more likely to resist disease and other problems, giving your plants the right soil and fertilizer along with regular watering, you will find that you will have a mainly trouble-free time growing your tomatoes.

If growing outdoors keep the plot free of weeds and debris where insects and diseases can flourish.

Rotate crops each year so that soil-borne diseases cannot get established, if growing indoors (e.g. in a greenhouse) change the soil each year.

Keep your gardening tools and equipment clean, this stops the spread of disease (and the tools last longer as well)

Remove any unhealthy leaves as soon as you see them, and remove any unhealthy plants if needed. Do NOT compost any diseased plant or leaves. Do not water the foliage of your plants, as most diseases thrive in damp conditions.

Leaf Mould

This is a fungal infection that attacks the foliage of tomatoes and is extremely common amongst tomatoes grown in greenhouses. You may sometimes see this fungus referred to as Fulvia fulva or Cladosporium fulvum, but it is now known as Mycovellosiella fulva.  The main symptoms of tomato leaf mould are yellow patches on the upper side of the leaves, with a pale, greyish-brown mould (sometimes purplish) on the underside of the infected leaf.  In severe outbreaks, the mould may also be seen on the upper surface of the leaf.  Eventually, the infected leaves will turn brown and shrivel but tend not to drop.  Occasionally the flowers and fruit may be attacked but this is very uncommon, an infected plant will give reduce yield and lack vigour in growth

The tomato leaf mould fungus produces a huge number of microscopic spores on each affected leaf, which can be spread by air currents, insects, hand and clothing.  These spores are resistant to dry conditions can easily overwinter on the surfaces of the greenhouse structure and on any debris left in the greenhouse, the disease develops and spreads rapidly in warm high humidity conditions.  Plants that have had the soil dry out and then soaked tend to suffer more severe attacks.

Leaf Mould – Non-chemical control

By providing plenty of ventilation, especially at night, to reduce the humidity in the air, and only watering in the early morning avoiding getting the leaves wet, will greatly reduce the risk of infection.  Do not let the soil dry out as this will weaken the plants and make them more susceptible to attack.  If at all possible keep the temperature below 21°C (70°F).  In order to increase airflow remove some of the lower leaves once the fruit has set. At the end of the season remove all plant debris and clean the greenhouse structure of a disinfectant such as jeyes fluid (tar oils) always follow the manufactures instructions on usage.

Grey Mould

Grey Mould (Botrytis) affects many plants not just Tomatoes.  It is a fungal disease that thrives in excessively moist conditions, such as in an unventilated greenhouse. The spores are around all the time and are air-borne and infect a plant through a wound, (such as caused by removing the side shoots).  Grey Mould will affect all upper parts of a plant (leaves, stem and fruit).  The symptoms of Grey Mould are patches of grey fur, underneath which the plant tissue rots.  As the infection matures black sclerotia about 2mm across are produced, which fall to the ground and act as a place for the spores to overwinter.

As there are no fungicides are approved for use against grey mould by amateur gardeners,  prevention is the only real way to fight this disease.  So keep the greenhouse well ventilated, do not overcrowd the plants, remove all infected  leaves, fruits or plants immediately.  The use of Jeyes fluid (tar oils) as a soil sterilant may kill the sclerotia as part of winter hygiene in the greenhouse.

Water or Ghost Spot

This is caused by the spores of Grey Mould infecting the fruit and then drying off as the conditions get warmer and drier. It shows as transparent rings on the stems and the fruit and does not cause any real damage.  To prevent it follow the advice above for preventing Grey Mould and also avoid getting water on the setting fruit.

Blight

This is the same as potato blight, so if growing outdoors avoid growing them together or near each other, also avoid growing where potatoes grew the previous year. You are much less likely to get blight on our tomatoes if you grow them in a greenhouse.  Infected plants develop dark brown to black patches on the leaves and may also have brown patches on the green fruit, more mature fruit will decay rapidly.  Destroy all infected plants as soon as you see them.

When wet weather is forecast from June onwards, protectant sprays are advisable, especially for outdoor tomatoes.

Verticullium Wilt

This is a soil-borne fungal disease that affects the roots of the plants, the first signs of infection are the wilting of the top leaves in hot weather and then the lower leaves start to turn yellow.  After a while, the whole plant wilts and becomes permanently limp.  If you cut through the stem just above soil level you will see brown staining in the internal tissues.  There is no cure for infected plants and they should be carefully removed and destroyed, avoiding spreading the infected soil.  So again prevention is the byword here keep weeds under control, keep your boots and tools clean to avoid spreading infected soil.

Stem Rot

This is caused by the fungus didymella, which infects the stem of the plant just above soil level.  The infection normally shows up as dead rotten patches that can girdle the stem.  Infected plants then wilt and die.  If the disease is caught early enough then it may help to spray with captan. although it is probably better to remove and destroy the infected plant.

Tomato Viral Diseases

Any infected plant should be removed and destroyed.  These viral infections cause a wide variety of mosaic patterns and distortions to the leaves, stunted growth and marbling patterns on the fruit.

Spotted Wilt

This is the most serious of the viral diseases affecting tomatoes as it spreads rapidly and can destroy a crop.  The young top leaves of the plant turn brown with concentric rings appearing on them as well. This virus is spread by thrips so controlling these will help to prevent the spread of this virus.

Mosaic Virus

This shows as pale green or yellow mottling on the leaves which may also curl and distort.  Another symptom is that the fruit will fail to set or will have a bronzed patchy appearance.

Enation Mosaic Virus

This virus causes the leaves to be so badly distorted that they will become long thin curled and twisted threads, mainly affecting the leaves at the top of the plant.

Blossom End Rot

Blossom end rot shows as a circular patch, varying in colour from greenish-brown to black, at the end of the fruit that had the flower (the end furthest from the plant). As this patch increases in size, it becomes sunken so that the fruit has a flattened appearance at the affected end. The blackened patch varies greatly: in some fruits, it is only 1cm (1/2in) across, while in others it is 2.5cm (1in) or more in diameter.

Blossom end rot is due to a lack of calcium reaching the fruit and the main reason for this is lack of water flow through the plant. Tomatoes that are grown in pots or growbags (where there is limited root space) are more likely to suffer from this, as they are more likely to have the soil around the roots dry out and hence stop the flow of water through the plant.

To avoid this problem keep the soil evenly moist at all times, and during hot days it may need watering two or three times during the day, which is better than one double dose.  Keep the air humidity down by proper ventilation.

Once a fruit has blossom end rot there is no cure for it.

Greenback

The fruits have hard green patches around the stalk which never ripen, this is generally caused by either too much sun, excessively high temperatures and/or a poor feeding regime.

Blotchy ripening

Parts of the fruit remain orange, yellow or pale green and never ripen, it is also known as whitewall, the causes are the same as for greenback.

Split Fruit

This is the result of irregular watering, either a lot of water has been applied after a dry spell in the greenhouse or heavy rain follows a drought outdoors.

Tomato Pests

Moth; The green or pale brown caterpillars of the tomato moth feed on the leaves and fruit causing a lot of damage. Remove the caterpillars by hand.

Eelworm: Both the potato root eelworm and the rootknot eelworm can affect tomato roots, the infected plant will have stunted growth, discoloured leaves and be severely wilted.  Plants infected with eelworms will usually have tiny cream-coloured cysts on the root.

Red Spider Mite: Tomatoes grown under glass are very susceptible to red spider mite. The mites lay their eggs on and feed on the underside of the leaves producing a reddish mottled look. In heavy infestations, you may see fine silk webbing on the plants, and the leaves lose most of their green colour and dry up or fall off. Heavily infested plants are severely weakened and may die.

Whitefly: Whitefly is a common sap-feeding pest, mainly of houseplants and greenhouse plants. Whiteflies excrete a sticky substance (honeydew) on foliage, which allows the growth of sooty moulds. The adult flies, which look like tiny moths, lay their eggs on the underside of the leaves.

Companion Planting