Event Report

Vegetable Gardening Tutorial by John Owen

13th February 2010

Fundamentals for plant growth

Soil (except for hydroponics)

Soil provides the primary source of plant nutrients and it provides a medium for root development that supports and nourishes plants
There is a variety of soil types, but the Meon Valley is predominantly chalky. i.e. light, stony, free-draining, moderately fertile, alkaline.
Tips for chalky soil

- Improve water retention by digging in plenty of well-rotted manure and humus-rich compost during the winter.
- In spring always apply a generous feed of slow release, balanced fertiliser (e.g. blood, fish and bone)

Tips for raised beds
- Ensure bed is lined with about 6 inches of well rotted manure to help retain moisture.
- Use soil rather than compost to fill up the bed in order to allow better nutrient and moisture retention.
- During winter, if not in use, cover with heavy gauge black plastic sheet, pierced with holes or slits to allow rain through. This will prevent weed growth and at the same time help to warm the soil prior to sowing or planting.
- Check the pH from time to time as the raised bed may well be less alkaline than the surrounding soil, and if necessary add lime in winter when growing beans and brassicas.

Water

Water is the vehicle that makes nutrients in the soil available to plants. It is also used in photosynthesis, which is the process that plants use to manufacture essential nourishment such as sugars and starch.
Most growing plants comprise 95% water
Of the water taken up by the roots of a plant only about 2% is retained, the rest is lost through transpiration.
Plants require far more water than one might realise.

Light

Light is the energy source for photosynthesis. The rate of photosynthesis is proportional to the intensity of light to which a plant is subjected.
Seedlings and young plants need a lot of light and will grow toward any light source (phototropism).
Even light distribution is important for seedlings to reduce legginess and encourage balanced growth.
Light also affects seed germination. In some plants it is necessary (e.g. celery and lettuce)
Light levels in late autumn, winter and early spring are not sufficient for vigorous plant growth. That is why, even in heated greenhouses, it is not possible to extend growing seasons significantly. However, by using supplemental lighting in the greenhouse it is possible to both extend the growing season and to grow more robust young seedlings and plants. The best form of supplemental lighting is provided by fluorescent tubes or a series of low energy bulbs.

Plants breathe through roots and foliage
Oxygen is essential for embryo and plant respiration. Without oxygen embryos will rot as will plant roots resulting in the death of the plant.
That is why plants and seeds will not survive in compacted or waterlogged soil.

Temperature

Temperature is a very important germination requirement. Most plants require relatively high temperatures to germinate (tomatoes and cucumber will not germinate below 10°c), but too high a temperature can inhibit germination (e.g. lettuce and grass will not germinate over 30°c).
Warm temperatures are also required for photosynthesis and therefore successful plant growth.
After germination it is important to maintain a fairly constant temperature around 15°c. If temperatures drop below 10°c many seedlings such as tomatoes will suffer a check to growth, which will have an adverse effect on the development of the plant.

Nutrients

There are two groups of nutrients:
Major or Macro nutrients comprising; nitrogen (N), phosphate (P), potassium (K), magnesium (Mg), calcium (Ca) and sulphur (S)
Minor or Micro nutrients (trace elements) comprising; iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), boron (Bo), molybdenum (Mb) and chlorine (Cl).
The main characteristics of macronutrients are as follows:
Nitrogen – promotes vegetative growth and is used liberally on foliage plants. It should only be used moderately on plants grown for flowers or fruit.
Phosphorus – this nutrient is used primarily for new growth and is particularly important for root development in young plants.
Potassium – this plays an important part in plant metabolism and is essential for good fruit and flower production. Potassium also helps to harden plants providing some protection in cold weather.
Magnesium – this is important for leaf and root development. In chalky soil magnesium availability is limited so Epsom salts should be used as a liquid feed or foliar spray.
Calcium – deficiency of calcium can adversely affect fruits. On chalky soil this is unlikely to be a problem.
Sulphur – used extensively for successful plant growth. However, it is not necessary to add sulphur as reserves in most soils are sufficient from use of other fertilisers used in sulphate form (e.g. ammonium sulphate as a nitrogen fertiliser) or pollution.
Micronutrients – these are needed in minute quantities for successful plant growth.
Nutrient deficiency - Deficiencies are often caused by the pH (acidity or alkalinity) of the soil. If soils are too acid or too alkaline they inhibit the release of nutrients (usually micronutrients) from the soil to the plant. Where deficiencies occur it is important not to overdose when remedying. Generally speaking, deficiencies can be addressed by using proprietary fertilisers such as ericaceous feed or tomato feed. Seaweed based fertilisers are generally a good natural source of trace elements.

Because most of the nutrients that have been used to grow vegetables are removed when the vegetables are harvested it is necessary to replace them every year in order to grow more vegetables. The need for nutrients can be reduced by digging spent vegetable matter back into the soil and letting it rot, but for many gardeners this is impractical as it ties up ground that could be used for more vegetable growing.
Some vegetables such as legumes (e.g. beans and broad beans) develop nodules on their roots, which have the ability to fix nitrogen in the soil. This is exploited in crop rotation, whereby nitrogen loving plants (those with lots of green stuff like brassicas) will be planted where legumes were grown the previous year.
Crop rotation is widely practised in vegetable growing and is an important way of preventing the build up of pests and diseases, as well as exploiting natural fertilisers as indicated above. The following table is a very simple example of how crops may be rotated:

Vegetables are always grown from seeds, sets or tubers and generally harvested within twelve months. There are one or two exceptions such as asparagus, which is perennial, and parsley, which is biennial.
Generally speaking, small seeds, such as lettuce, radish, spring onions, carrots, rocket are sown in drills and thinned as they develop and large seeds, such as peas, beans and broad beans that can either be planted directly into their final growing position or into pots or trays and planted later in their final growing position.
When planting in trays or pots it is important to use seed compost or a mixture of peat (or other inert medium), grit and vermiculite. Plants do not require nutrients until after the seeds have germinated and the first true leaves have started to develop. In fact the presence of nutrients can inhibit seed germination, which is why using multipurpose compost can sometimes give poor germination yields. To avoid damping off of seedlings in trays and pots it is advisable to spray or water the compost, before germination, with a solution of Cheshunt compound or some other copper based fungicide.
The soil should be moist and fairly warm (more than 15˚c) when sowing seed and after sowing the soil should not be allowed to dry out, nor be too wet or the seeds will rot.
The best way to give plants an early start from seed is to warm the soil up before planting. A good way to do this is to cover the soil for about 3 weeks prior to sowing with a sheet of heavy black plastic with holes cut in it to allow rainwater to get to the soil
Protection of the seeds from birds, cats and mice is important, and can be achieved by pegging mesh or horticultural fleece over the soil.
For seed sown in drills it will be necessary to thin out the seedlings regularly as they develop so that the plants have space to grow.
Larger seed (beans, peas, broad beans) can be pre-soaked before sowing to speed up germination. These larger seeds are often sown in pots and transplanted to their final growing positions when they have developed into small plants.
Seed for plants such as cabbage, sprouts, leeks, cauliflower, courgette, ridge cucumber, outdoor tomato and broccoli are usually sown into trays and the seedlings transplanted into pots before planting in their final positions.
At no time should the plants be allowed to dry out, and once established, the plants should be fed regularly with the appropriate fertiliser. As a general rule, plants with a lot of foliage should be fed with a nitrogen rich fertiliser, root crops with phosphorus rich fertiliser and fruits such as tomato with potassium rich fertiliser.
The objective is to ensure rapid, uninterrupted growth that will yield fresh, crisp, succulent crops.

Growing some of the more popular vegetables

Tomatoes

Two types of tomato plant are available - indeterminate (cordon) and determinate (bush).
Cordons are trained up canes or string and side shoots pinched out when they appear. The plant is stopped (growing point pinched out) after 6 to 8 trusses have formed (greenhouse) or 4 to 6 trusses for outdoor plants. Cherry tomatoes will typically support a greater number of trusses in a season than plants with larger fruits.
Contrary to the advice on seed packets it is a good idea to provide some support for bush tomatoes to keep foliage and fruit off the soil. The side shoots are left intact on these plants.
Avoid using growbags. Grow directly in soil or in large pots (10 litre min.)
Regular watering (daily) is needed for established plants and weekly feeding after the first truss has set (formed fruit).
A major problem with tomatoes is blight, which is present in most gardens. It is a fungal disease (phytophthora infestans), who’s spores become active in warm damp conditions, usually June and July. There is no cure for blight so prevention is the only option. As soon as blight conditions are present (warm and damp), it is advisable to spray plants weekly or fortnightly with a copper based fungicide or Dithane. Alternatively the plants can be draped in horticultural fleece, which traps any blight spores that might be carried in the rain.

Potatoes

Potatoes take up a lot of space, but for people with small gardens there are ways of enjoying limited supplies of new potatoes.
First early seed potatoes can be planted in barrels or very large pots (25 litre min) from late March but they will need protection from hard frosts. Planting early should enable the crop to be harvested and a second crop planted in mid summer to provide some more new potatoes in the autumn.
The most common ailments to affect potatoes are potato blight (see next paragraph), scab, keel slugs, and wireworm. There is little protection available to address these problems, although it is alleged that soot will deter keel slugs.
Potato blight is the same disease that affects tomatoes, and has two phases - the first attacks the leaves, the second attacks the potatoes themselves. At the first signs of infection cut the foliage back to 5cm (2in) from the ground. This will prevent the blight from getting to the potatoes themselves, but with no foliage, the potatoes will not give of their best, but they will continue to grow for a month or so. If your potatoes are attacked by the blight, there is no cure. For prevention use same methods as for tomatoes.

Beans

Broad beans are very frost hardy and will germinate in a soil temperature as low as 2°C (35°F). Sowing time is around late March. However if your soil is free draining some varieties can be sown in early autumn when the weather is cooling down. This should give a crop about three weeks earlier than a spring sowing. However, seeds sown in trays or pots in the greenhouse prior to planting out will probably achieve the same results.
When sowing seed directly into the soil do so in shallow drills about 2 inches deep and 10 inches wide. Broad beans generally need support and this can be provided by placing canes (3 to 4 feet tall) along either side of the drill and threading twine around the perimeter and across the line of the drill.
A week or so before sowing the seed add a nitrogen feed to the soil. Although Broad Beans produce their own nitrogen in little nodules along the roots, this does not happen until the plants begin to grow strongly, so a little extra nitrogen at the beginning will get them off to a good start.
 Runner beans are able to extract nitrogen from the air and fix it in little nodules on its roots more quickly than broad beans. For this reason, the soil should not be rich in nitrogen, which would only result in lots of leafy growth and few beans. The ideal soil is deeply dug with lots of well-rotted organic matter (peat or peat substitute is ideal) incorporated. This will ensure that the soil is capable of holding lots of water, a key need of runner beans. Prepare the soil in February or March and incorporate a couple of handfuls of bone meal per square metre.
It is important not to overcrowd runner beans; plants should be at least 15 inches apart.
Runner beans produce a lot of foliage, so a row approximately 2 metres tall can produce quite dense shade. Therefore if the ground immediately on either side of the row is to be utilised then the row should run north to south, otherwise if planted east to west the northern side of the row will be in permanent shade.

Carrots

Carrots require no additional fertiliser, but they do need a lot of water. Carrots are relatively easy to grow and the only major problem is carrot root fly, which can easily ruin a whole crop and is not easy to control, but these are a few precautions that might help.
Thinning out the seedlings will release the scent of carrots, and attract the attentions of carrot fly. To avoid this, perform this activity in the evening when the carrot fly is not about. Ensure that any soil disturbed by the thinning process is firmed back down with your hand - carrot fly lay their eggs in loose soil around the carrot seedlings.
The main danger period is mid-May when the flies are most common. One simple solution is to postpone sowing maincrop varieties until June. The use of pelleted seed is another alternative - it will reduce the need for thinning.
Covering the plants with enviromesh or fleece should prevent the flies laying their eggs.
Planting next to onions or spring onions can sometimes work because it confuses the flies’ sense of smell (allegedly).
Sowing carrots late (June onwards) should also prevent attack because it is after the time for egg laying.

Aphids (green and black)

These can affect most plants and in large numbers they can do serious damage. Regular checking for these pests is essential so that they can be dealt with before they build up to an infestation. There are proprietary pesticides that can be sprayed on food crops, or a solution of washing up liquid can be used if preferred. In the case of broad beans it is possible to minimise black fly attack by pinching out the tips of the plant when they have grown to their allotted height.

Whitefly

A real pest that is extremely difficult to control if it becomes an infestation. It mainly affects greenhouse crops and brassicas. Regular checking for this pest is necessary and as soon as it is seen it needs to be sprayed with an appropriate pesticide, preferably earl morning or evening.

Slugs and snails

They are indiscriminate feeders and will damage most crops if not controlled.
Unfortunately there are no silver bullets to eradicate these pests and the legion of so-called remedies are too numerous to list here, but here are a few:
 Slug pellets are quite effective. Slug traps, if you have enough of them can also be quite effective. Caffeine solution (cheap instant coffee), or dilute copper solution can be used to spray plants under threat. Wood ash or broken eggshells sprinkled liberally around vulnerable plants can act as a deterrent.

Leek moth

Adult moths overwinter in plant debris and lay their eggs in April and May. The caterpillars hatch about a week later and tunnel into the leaves to feed. They mine the leaves, leaving the outer skin intact, eating down through the outer leaves to feed on the inner leaves and growing points of stems. On onions, they mine the hollow leaves, sometimes boring down into the bulb. The caterpillars feed for about a month before crawling back up the leaves to pupate in cocoons. These produce a second generation of caterpillars to cause damage from August to October.
To protect against leek moth clear away all plant debris at harvest. Dig over the soil to disturb overwintering adults and pupae.
Check leek plants for damage in the spring (i.e. white streaks on the leaves). Remove and destroy any caterpillars and pupae visible on the leaves. Destroy severely infested plants.
Protect the crop, from seedling stage onwards, with horticultural fleece to prevent adult moths from laying eggs.
Later plantings after May, may avoid the first generation of caterpillars.

Caterpillars

These are mainly a problem with brassicas and emerge from the eggs of cabbage white and similar butterflies. There are proprietary pesticides that will get rid of caterpillars, but a better solution is to cover the plants with a fine mesh or horticultural fleece, which prevents the butterflies laying eggs on the plants. This solution has the added benefit of protecting the plants against birds.

Flea beetle

This pest attacks all members of the brassicas family, including swede, radish, turnip and rocket, by drilling holes in the leaves of the plant. Apart from being unsightly (e.g. rocket leaves) it has the effect of weakening the plant by reducing the amount of leaf area available for photosynthesis. It is a real problem in the Meon Valley, as it breeds in the fields of oil seed rape (also a brassica). There are pyrethrum based pesticides that can be used for control, but covering the plants with fine mesh (enviromesh) or horticultural fleece is more effective.

Cabbage root fly

This is a serious pest affecting all brassicas. The fly lays its eggs near the stem of the plant and when the larvae emerge below soil they eat the roots of the plant. Two ways of minimising risk of attack are to either dip the roots of the plants in a dilute solution (1-5%) of Jeyes fluid before planting, or to lay down felt or fibre mats at the base of the plants.

Seed sowing

Compost for seed sowing should be moist or damp not wet. The temptation to give a bit of extra water to trays or pots of seeds should be resisted; it can easily cause seeds to rot.

Seedlings

Seedlings too only require minimal water (moist or damp compost). If the compost is too wet the seedlings will succumb to a variety of fungal infections and damping off will occur. i.e. the seedlings will rot and die.
If damping off occurs remove affected seedlings and spray the remaining ones with a copper fungicide (Cheshunt compound).

Watering

This is probably the most important aspect of vegetable culture and the one that can cause many problems if not done correctly at all stages in the cultivation of plants.
Regular watering of established plants is crucial; it will ensure healthy, fully developed crops and avoid many of the problems caused by irregular watering, including the following.
Tomatoes – blossom end rot, splitting, blossom drop
Carrots – split roots, woody core
Cabbage – split hearts
Cauliflower, potato, runner bean, broad bean – undersized crops
Radish, beetroot – woody, undersized roots.

Companion planting

This is a way of reducing the risk of attack from certain pests by growing certain plants close to each other, as with onions and carrots referred to above. Another example is the use of plants such as calendula, which attract hoverflies (an aphid predator) to deter aphids. A further example it the use of African or French marigolds in the green house, where their aromatic leaves is said to deter whitefly.

Fungicides and herbicides

When using proprietary products it is important to read the instructions on the label.
As a general rule fungicides fall into two types: contact and systemic.
For vegetable treatment use only contact herbicides and pesticides, as these products are active for relatively short periods and can be washed off any produce before consumption.
Systemic products are absorbed by the plant and remain active in the tissues of the plant for up to six months and are generally considered inappropriate for use with vegetables.
There are, however, some exceptions such as Provado Ultimate Bug Killer, which can be used with selected crops such as tomatoes.

Physical barriers in pest and disease control

Some people prefer not to use chemicals when growing vegetables and those that do are finding it increasingly difficult to find effective products as most have been withdrawn from sale.
One alternative is to use biological control for some pests, but this is relatively expensive and is only moderately effective.
The most effective control of pests and some diseases is achieved with various forms of physical barriers that prevent the pest coming into contact with the vegetable crops in the first place.
Simply laying fleece or mesh over plants, as suggested in many books and catalogues, is not the best method. It is better to provide some form of framework to support the barrier so that it is not in contact with the growing plants.
For most plants such as carrots, salad crops, potatoes, French beans, leeks and cabbage the fleece or mesh can be supported with large hoops to form cloches.
For larger plants such as sprouts and purple sprouting broccoli larger supports are needed that are strong enough to deter large birds (woodpigeons). Something along the lines of a mini fruit cage.
It requires a lot of effort to erect and dismantle physical barriers, but they are probably the best way of ensuring that you and not pests enjoy the fruits of your labour in the vegetable garden.

References

Essential reading: The Vegetable Expert – Dr. D G Hessayon
Knowle Nets (01308 424342) Netting and screening materials
G-tex (01933 664411) Horticultural fleece and weed control (membrane)
Agralan (01285 860015) Pest control products (inc. enviromesh)

Web sites: 
www.gardeningdata.co.uk
www.gardenaction.co.uk
www.gardenorganic.org.uk