Summer Tomatoes

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Background - Types - Seed - Seedlings - Soil - Planting - Growing - Harvest - Problems

Tomatoes are quite possibly the most popular and widely grown fruit in the UK, however that dose not mean their easy to grow well! Tomatoes are well known for being capricious and suffering from many ills. That said they can be truly amazing when grown with attention and fresh picked, they are nothing like what you can get in the supermarket.

Tomatoes are a complex mess of sugars, acids and numerous different tastes that all Intermingle when they are ripe and the cells start softening, this blend of tastes just doesn’t happen with tomatoes that are chilled and harvested before they are fully ripe. (for those interested look up the Flavr Savr tomato a tweaked tomato designed to alter harvesting and with superior taste when sold in the supermarkets)

Type of Plant

Tomatoes are Mexican natives and perennial in their native country (resulting in truly incredible plants) and has spread across almost the entire world in various forms. In the UK it dose not overwinter unless given heated care and suitable light however due to its quick growth this is often not considered worth the effort. The tomato hybridises very well and there are now several hundreds of cultivars that can be tested but they all fall under two divisions.

Determinate

Determinate are the bush forms of tomatoes, these cultivars are comparatively small, growing from 1-3ft and have a limited cropping period of about two weeks. After the flower has formed on the end of its stems the plant is unable to continue growing and therefore finishes its crop before dyeing You do not take suckers off a determinate plant as it requires all the energy it can gather. Determinate plants are ideal for containers.

Indeterminate

An indeterminate tomato is able to grow, potentially forever as it dose not produce terminal flowers, instead this tomato sets fruit on lateral flowers and continues to grow throughout the season. This means they require a great deal of staking and they can produce vast amounts of fruit. As they live until the frost it is possible to keep these as perennials under glass, however it is not generally considered productive.

Types of fruit

It is also possible to categorise tomatoes by the type of fruit they set, there are many different shapes however the main ones are listed here:

Globe: This is the most commonly cultivated tomato shape, the standard round tomato.

Cherry: This small tomato is often used in salads and is typically stronger flavoured than large tomatoes.

Oxheart: These tomatoes are large and multi-lobed looking like the chambers on a heart. Often slightly irregular they are common sauce tomatoes

Pointed: A slightly more unusual shape, these are quite distinguishable but have no other distinguishing features.

The main things to keep in mind when choosing cultivars (apart from a favoured taste) is firstly if it is a shrubby determinate or a sprawling indeterminate, if it is better suited to indoors or outdoors and what you want to do with the fruit (i.e. salads or sauces)

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Sowing Seed

Seed can be sown over a long period of time for tomatoes however it is worth noting most cultivars crop between 60 and 90 days after sowing (although this can be affected by the weather). If you have a warm greenhouse or conservatory and you want to grow them indoors you can start as soon as January however for outside cropping, whilst you still should sow indoors it is wise to wait a bit (March) as tomatoes are tender in the UK. Tomatoes will want to be kept slightly moist and at about 18*c throughout germination if this is problematic then a heated propagator or a clear plastic bag over the pot is beneficial Covering the pot or seed tray with a small layer of vermiculite or multi-purpose compost is a good idea to stop the seed drying out. Seedlings should appear after 5-7 days. It is important to keep a high light level whilst growing tomatoes as they will otherwise tend to become leggy where they will produce an unproductively long stem. If this happens then plant them out slightly deeper as the entire stem of a tomato can produce roots.

After the first pair of leaves are developed then gently prick out the plants holding them by the cotyledons (seed leaves) whilst supporting with a pencil or such and pot into small separate pots.

Sowing directly into the ground is not recomended for many reasons, such as the cold but also when transplanting, the root structure changes from taproot to fiberous and therefore is far more efficiant, giveing you better young growth.

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Seedlings

If you are unable to grow from seed (or just don’t want 30-40 plants) then we sell a range of seedlings ready to pot up and plant out, as they are still young then care should be taken to avoid the last of the frosts if outside and they should be taken care of to ensure they get enough light. Seedlings ready for planting should have stems of approximately pencil thickness, be dark green and not too leggy. Ideally they have short lengths between leaf nodes however some indeterminate cultivars are prone to have long internodal stems.

For the perfectionist, use a fan to shake the stems of mature seedlings as this helps them develop stronger roots.

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Prepairing the soil

Tomatoes like warm slightly moist soil and therefore benefit from soil preparation such as laying black membrane or plastic over the ground they will be planted in as this preserves heat and moisture. Tomatoes are remarkably hungry plants and will readily use all and any nutrients you care to add. Increasing the organic matter content of the soil should be done and they can grow well with incredibly rich soil. If using compost use John Innes 3 with 1/3rd multi-purpose for quicker root establishment.

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Transplanting

It is possible to plant directly into the pot or grow bag at this point, if you have good weather and good soil then that is a perfectly viable option, however if there is still cold weather about then it would be good to at least allow them to acclimatise and reduce the shock to the plant. It is possible to plant the tomato slightly deeper which stimulates more roots to form and even to plant the tomato in a trench with the tip poking out. This is particularly effective as the roots will be forming in the warm topsoil.

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Growing on

Indeterminate

Indeterminate tomatoes need more attention than their determinate relatives, it is always advisable to remove unproductive side shoots and to use canes for support. These plants can grow truly massive but are easy to pinch out and keep to the size you want. The typical pinching out point is after ~6 trusses have formed but that is by no means a rule set in stone.

Determinate

Determinate tomatoes are much easier to care for as they are small and do not need side shoots removed. Canes and other supports may still be useful however as they can produce heavy loads that can snap the stems. If you are growing late variates outside rather than in the greenhouse it may be worthwhile removing a few side shoots to increase air flow and reduce blight.

General Care

All tomatoes will benefit from an application of a potash fertilizer when the first flowers form and when being watered after that, especially those grown in pots. Tomatoes grown in the ground need less watering and feeding than those in pots or bags however they should still be looked after and not allowed to dry out too much.

If grown in a greenhouse a simple way to support tomatoes is to tie some string or wire to a ceiling bar and peg it into the soil with a bit of slack, then grow the tomato lightly twined around the string. This allows tomatoes to reach great height. Tomatoes tend to suffer in high heat and  they can have greatly reduced crop yields and poor ripening in temperatures above 35*.

Whilst tomatoes normally set fruit readily and are able self pollinators, in a greenhouse this can be aided by shaking the plant slightly in much the same way as you would a chilli.

Watering a tomato plant is best done carefully to avoid splitting, Idealy you want to water 1-2 times a week in most soils and ensure the water goes down to the deep roots rather than purely the surface roots. This allows the tomato to weather heat better and allows a stable water uptake reduceing both splitting and blossom end rot.

Fruit Forcing

For an extremely quick harvest (if the end of the season is coming and your plant has yet to fruit) it is possible to stimulate fruiting by reducing water and damaging the plant roots slightly. This will cause the plant to believe it is under threat and try to reproduce, however this is widely reported to have a negative impact on quality.

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Harvesting

The harvest is perhaps the biggest reason home grown tomatoes taste superior to shop brought tomatoes, shop brought ones are picked before they ripen and then brought on chemically to the bare minimum stage they can be sold, this often means they do not have time to develop the flavour you get on home grown plants.

The ideal tomato has a high acidity and a high sugar content, to that end you want to harvest in the evening after the plant has been active throughout the day and ideally not to have watered the plant in the last 24h as this can lead to slightly watery tomatoes. In addition avoid putting tomatoes in the fridge after harvest as this retards the ripening still continuing

Tomatoes have a long harvesting period but there are times when the tomato is at its very best, as the fruit just starts to break down slightly and the flavours mix is widely regarded to be the best time for eating. Fruit that will not ripen can be taken indoors still on the vine and placed in a warm place it will continue to ripen off the plant. With extremely stubborn fruits try placing with a chopped up apple.

Tomatoes grown in a slightly acid soil tend to have a deeper taste than those grown in an alkaline soil.

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Whats wrong with my plants?

Tomatoes are the subject of a number of problems, some treatable, some not however all of them should be taken care of quickly.

Condition

Description

Cause

Treatment

Greenback

Parts of the fruit remain green and hard on the outside.

Can be caused by many things such as excess light and heat. Removing the bottom leaves helps avoid disease but can exacerbate this.

Hard to treat unless the cause is known.

Whitewall

Some parts of the inside fruit are yellow or white.

Caused by the same problems as Greenback

Again hard to treat unless there is an obvious culprit

Splitting

The fruits of the tomato split or crack.

Most often caused by excessive or irregular water levels, the fruit absorbs too much water and is damaged.

Reduce watering and try to harvest slightly earlier on tomatoes prone to splitting. Pick tomatoes before rain and do not water the fruits!

Mottled Leaves

Mottled leaves such as brown/black/yellow patches appearing

This is most often caused by low nutrient levels, if only occurring on old leaves then this is easy to fix. More serious on younger leaves. May also be the start of tomato mosaic virus.

Feed with a balanced high quality fertilizer, Vitax Q4 is ideal as it contains high potash and all trace elements.

Curled Leaves

Leaves curl inwards.

Possibly caused by a virus, this may also be caused by rapidly changing temperatures and sap sucking pests such as aphids.

Inspect leaves for aphids and if found, treat with Py spray or remove by hand. Avoid treating whilst weather is hot. If not found observe closely.

Oedema

Leaves and stem may swell and develop brown corky tissue.

This is caused by excess humidity and water. it is not overly dangerous but is a sign that water is not ideal.

Decrease watering and attempt to increase air flow, consider removing the bottom branches.

Virus damage

Leaves develop splotchy yellow patches which may turn into necrosis. Leaves may also curl.

This can be caused by any number of viruses, none of which can be treated. Look for signs of aphids which are regular carriers of these diseases.

Destroy the plant, if left alone it stands a good chance of infecting other plants in your garden.

Tomato Leaf Mould

Leaves develop a soft furry growth, generally on the lower leaf side. Leaves do not drop but instead shrivel up

This is a fungal infection generally increased by a high humidity. It only seriously affects plants after 6 weeks so if the plant is already cropping well it may not be worth treating.

Chemicals that give control of blight such as Bordeaux mixture may provide some control but there is nothing specificity used for it.

Late Blight

Late blight is the bane of tomatoes and potatoes, black marks appear on the stem and the plant turns yellow and stunted.

Blight is untreatable and chemicals only give minimal control. Use of Bordeaux gives protection however. Look up the smith period for your location. Less common on greenhouse crops.

If infected, immediately harvest any healthy tomatoes and destroy the plant.

Blossom End Rot

A black, sometimes hard sunken patch appears on the bottom of the tomato fruit.

This is caused by a lack of calcium, however calcium itself is highly prolific in most soils. The issue is the transportation of calcium which can be difficult for the plant, requiring a good water flow.

Discard affected fruits. Increase regular watering and avoid using fertilisers, especially nitrogen based on dry soil. feed with super phosphate of lime to improve roots.

Didymella (tomato stem rot)

Causes black spots on the lower stem that move up as time progresses. causes plant to wilt when the rot girdles the stem. Can affect the fruit

This disease is prevalent in cool wet weather and is less common in greenhouses.

Destroy the plant to prevent infection of other plants.

Verticillium wilt

Causes yellowing and shrivelling of lower leaves and wilting as the plant chokes the xylem (water carrier tissue)

Verticillium wilt is very common and worryingly can be transmitted as easily as stepping on infected ground. It attacks the stem and then hides in xylem tissue the plant blocks up. In damp cool weather, with less heat stress the plant may appear to recover.

Avoid replanting in the area if possible Applying a high nitrogen feed and regular watering will help sustain the plant and stimulate meristem growth to form new vascular material.

Poor fruit production Tomato plants occationally refuse to set fruit and may put on extra growth.

This can be caused by a few different things, firstly check if the tomato is indeterminate or determinate and if you are sideshooting it correctly.

It can also be caused by an overabundance of nitrogen, especially when no potash has been applied.

A third option is a high heat, dispite being mexican natives tomatoes do not like to set fruit or ripen above 35*

In the first case, indeterminate plants should be sideshooted quickly and this will help encorage fruiting on new growth.

Adding potash will encorage fruiting and ripening and counteract excess nitrogen.

If the weather is overly hot then try increaseing venting or damping of a greenhouse.


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