Vegetables And Herbs For The Greenhouse

Tomatoes
SOW DEC, JAN, FEB, MAR
harvest MAY, JUN, JUL, AUG, SEP, OCT

Tomatoes are the classic greenhouse plant and one of the most popular grow-your-own crops. When grown successfully, they are notoriously heavy croppers, but it is probably the huge range of types available that makes them so seductive. In recent years, supermarkets have begun to pick up on our interest in very small or very large — and above all very tasty — tomatoes, but not before plenty of gardeners had already resorted to growing their own, happily and successfully. Tomatoes are generally considered a reasonable challenge to grow, so that means there are a lot of good gardeners out there!

Cultivation
DIFFICULTY They require plenty of attention, but the rewards are great.
SOW Two seeds to a pot in modules or small pots. Put them in a heated propagator at 16-18°C (60-65°F). Sow in mid- to late winter for growing on in a heated greenhouse (13°C/55°F), delay by about a month for an unheated one. If two seedlings emerge, nip out the weaker one.

PLANT Pot on into larger pots as necessary; don't over-pot, but don't allow the plants to become pot bound either: they need to be able to grow fast and freely. When they have reached about 20-25cm (8-10in), plant them out into the soil borders — spacing them 60cm (2ft) apart — or two to a growing bag or into 30cm (12in) pots.
'Sung°Id' has long trusses of small fruit with a sweet flavor that develops well under cover.

CARE Immediately after planting, give each plant a good watering in, then continue watering, but not over- generously, until the first flowers open. Increase the amount you water as the fruits start to swell. Start feeding with liquid tomato feed as soon as the plants reach about 15cm (6in) tall, or even before. After planting, feed once a week, increasing to twice a week once the first fruit have set. Although tomatoes like warmth, they don't like excessive heat. Ventilate well, especially as temperatures reach 21°C (70°F) or more. Support cordon types on canes, or strings fixed to overhead supports, and pinch out the sideshoots that appear in leaf axils when they are about 2.5cm (1n) long. Bush varieties can be left to get on with it unsupported and without any pinching.

HARVEST Pick tomatoes as soon as they turn fully red; left on the vine they will soften and split. In a heated greenhouse you can look forward to crops from late spring; an unheated one will start ripening fruit in early summer. The fruit will continue to ripen until mid-autumn in a good year. When the plants have to be cleared away, any final green fruits can usually be ripened in a dark place indoors. You can also pull up the entire vine and hang it upside down to ripen.
STORAGE If you have a glut, try roasting them in the oven with olive oil and garlic, then freezing them for using in sauces later in the year. Alternatively, make chutneys and relishes.

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Propagating From Seed

Carrots
SOW JAN, FEB, MAR, SEP harvest MAY, DEC
Baby carrots are a sweet addition to salads and are great cooked, too. You won't get huge roots under cover, but they are worth having. They're best in soil borders, or early crops can be grown under cold frames and cloches in the garden.

Cultivation
DIFFICULTY Easy; average input.
SOW Thinly in shallow drills in greenhouse borders or under cover in the garden. Cultivate the soil well beforehand so it is not lumpy. Avoid areas that have had manure added in the last year. Allow 10-15cm (4-6in) between rows.
CARE Water well and regularly. Thin if necessary as the plants develop. Remove weeds carefully to avoid disturbing the developing roots.
HARVEST Pull baby or salad carrots as soon as the first ones are big enough to use. Take alternate roots — this gives the remainder a little more space to grow. STORAGE Best pulled and eaten immediately. If necessary, store them in a plastic bag in the fridge for a few days.

Catch crops
Catch crops are a very popular notion out in the vegetable garden and there is no reason why they can't be equally successful in the greenhouse. Basically, they consist of fast-growing vegetables or those that can be eaten when still quite young or small, often called baby, or mini, veg. You plant them early or late in the year to get an extra crop, or squeeze them in any space that appears among other longer-term plants to get a quick crop during the main growing season. Because they are not there for long, they don't need much room and don't restrict the growing activities of their bedfellows. You do need to be well organized to get the seeds in whenever and wherever there is a space, and then be patient to allow them to do their thing. Beetroot, carrots, radishes, a huge variety of salad leaves and turnips are all proven (see under the individual entries), but you could try others.

Look out for...
Very early crops, especially those under cover, should not suffer from carrot fly, the biggest pest of carrots, which is active from late spring. If you find it is a problem, avoid thinning, as the smell attracts the females, or thin just before shutting up the greenhouse for the day. The smell will dissipate overnight.

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Containers For Greenhouses

And finally..

Water the pot really well, drenching it to settle all the compost around the roots. With some plants — such as alpines and cacti — you can add a mulch, for example grit or gravel chippings, for decoration and to stop weeds from growing on the surface. The mulch will also reduce water evaporation and prevents the surface compacting, which makes watering difficult.

Hardening off and planting out
If seedlings and cuttings are to go out into the garden, they need to be hardened off beforehand. Planting them straight out into the garden without some gentle acclimatization will give them a shock that sets them back, and may even kill them. You've spent weeks or even months getting them this far, so it isn't worth taking shortcuts at this stage. Young plants bought from under-cover displays at the garden centre should also be hardened off before planting out.

Take your time
Young plants raised in the protected environment of a greenhouse or poly tunnel will be delicate. All their shoots and leaves are soft and tender, and need to be toughened up gradually in order to survive outside. Start hardening off about two or three weeks before you want to plant out. Pay attention to the weather, not the date, and don't try to harden off in cold, wet or blustery weather — months of work can be destroyed overnight by impatience at this stage.

If you have a cold frame, stand trays and pots of plants in it. Open the lid on walnn, balmy days and keep it closed on cold, wet ones and at night. If you don't have a cold frame, you'll need to establish a daily routine of taking trays and pots in and out of the greenhouse. After a couple of weeks, leave them out on fine nights, covered with horticultural fleece.

Planting out
Choose a warm day to plant out. If you're planting tender vegetables or bedding plants, this must be after the last frost. Again, don't hurry — a few more days in the pot won't do as much damage as a frost at this point.
Even fairly tough plants like sweet peas need gradual acclimatization if they have been raised in the greenhouse. It is never worth hurrying hardening off.

Plant problems and remedies
Unfortunately, while you're carefully nurturing your plants inside your greenhouse or poly tunnel, there are many pests and diseases waiting for the opportunity to make the most of a free lunch. In fact, many of them are already present in the soil or among plants you bring in from elsewhere, so even if you raise your plants perfectly, you may experience problems. The best thing to do is to be vigilant and take action the moment that you spot anything going awry.

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A Healthy Greenhouse

Heated propagators

Heated propagators usually look like the better-quality unheated ones, and work in the same basic way, but have the advantage of a heating pad sandwiched into the rather thicker base. There are two types: fixed temperature and thermostatically controlled.

The fixed-temperature variety provides heat at approximately 19°C (66°F), which is ideal for germinating a range of seeds. They are generally reliable and really speed up germination of most seeds that require heat; they can mean the difference between success and failure with some of the more challenging ones. They are not expensive and are well worth the cost. Bear in mind that without a thermostatic control these propagators will provide heat even on the warmest days, so you'll need to check young plants regularly.

Don't forget
A small heated propagator is unlikely to be able to protect tender plants from frost in the greenhouse in winter.

Thermostats can go wrong. Check that your thermostat is always delivering the heat it should be by putting a thermometer inside the propagating unit.
Thermostatically controlled propagators.

The thermostat adds value but also expense to a heated propagator. These models are at least twice the price of the fixed-temperature sort for the same size, but they do have their benefits: they are more efficient, so they should use less electricity; they won't overheat your plants on a warm day; and they can be set at the precise temperature particular seeds need for germination or cuttings require to root. They are also available in larger sizes, making them suitable for overwintering a

Use a heated propagator with a thermostat for seeds that need a higher temperature to spring to life. small selection of plants if necessary. However, if you plan to go in for large-scale propagation, you might be better off making your own (see box, below).

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Greenhouse Alternatives, Paths And Other Hard Surfaces

Fans
Some greenhouses are fitted with a mechanical fan in the gable end opposite the door and work as the air flows through them. Opening the door or the vents should set them in motion, but their effect is minimal. Alternatively, if you have electricity installed, you could have a motorized fan. Extractor fans of the sort installed in bathrooms and kitchens are also suitable for greenhouses. Choose one with a thermostat so that it runs only when the greenhouse reaches a certain temperature, and make sure it has louvred 'storm guards', which drop into place when it is not working, to avoid draughts. Some greenhouse fan heaters can be set to run without the heating element. However, unless the thermostat set-up is particularly sophisticated (sensing heat as well as cold), they will run more or less continuously, which could prove to be quite costly.

Solar-powered extractor fans are available at a price comparable to electric ones, but their extracting abilities are not nearly as good. Fans are rated by the cubic volume of air they can shift in an hour. For a smallgreenhouse of 2 x 2.5m (6 x 8ft) you want a fan that shifts about 300cu m (10,000cu ft) an hour — solar ones provide less than one sixth of this.

Don't forget
If you open the door in summer, it is worth considering fixing a net over the space to keep birds out. A warm greenhouse is also a rather popular sleeping area for cats, who you may want to discourage.
When it comes to ventilation, sliding doors are best, because they can be opened just a crack during cooler weather and fully when it is warmer.

Door
The door is an invaluable source of extra ventilation on hot days, and can be used to increase air circulation on days that are too cool for the automatic vents to work. Sliding doors are the most versatile as they can be opened in tiny increments. They also don't need propping to prevent them slamming in a breeze. Nevertheless, be wary of opening them on windy days — strong draughts are not wanted inside a greenhouse, because they cause havoc among plants and can even adversely affect the structure itself.
Doors are usually the only form of ventilation in a polytunnel. Very basic, roll-up types can be secured partly open, as can pricier sliding ones; polythene hinged doors may slam, but at least they won't break.

Avoiding wind damage
On very windy days, check that your automatic openers are up to the job and don't allow your vents to bang to and fro. Tie them down temporarily if necessary. If the wind does get inside a greenhouse, it can behave like a set of bellows, creating quick changes of pressure, which may pop panes out of place. For this reason, if a glass pane ever gets broken you must replace it straight away, otherwise it will start a domino effect, and more will go.

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Choosing The Right Greenhouse

Conifers are shady all the year around, but on the plus side, they do make a good windbreak in an exposed site. They are also less likely to drop bits onto your greenhouse, although bear in mind that all trees lose their leaves and twigs at some time or other.

Don't take the idea of an 'open' site too literally, however. Greenhouses cannot withstand the full blast of winter storms, nor endless strong winds, which also have a detrimental cooling effect. If your site is particularly exposed, consider erecting (or growing) a windbreak on the windy side. This is usually the south-west side, since this is where the prevailing weather comes from, but bear in mind that northern and eastern winds are much colder and will have a much stronger influence on conditions inside your greenhouse in winter. If you think you might need a windbreak, position it to give your greenhouse the most efficient shelter possible.

The best windbreaks are those that slow the wind, rather than blocking it
altogether. This means that hedges are most suitable, while fences with an open structure are more likely to be successful than close-boarded varieties, such as larch lap. With the latter, you may end up tunnelling the wind through a narrow space, which will increase its strength, or creating turbulence on the lee side of the fence, just where your greenhouse is.

Frost pockets
It makes sense to avoid putting your greenhouse in or anywhere near a frost pocket. If you aren't sure whether your garden has any, take a look around it on a frosty day. The coldest places are where the ground stays white and frozen longer than anywhere else.

Hot air rises and cold air sinks, so in a sloping garden the low-lying areas get much colder than those higher up. Where the co d air is trapped by hedges or buildings, the area will stay colder for longer, too. If you must position your greenhouse in such a spot, you might be able to improve matters by making gaps in hedges or fences, which will allow the cold air to flow on down the hill.

Shelter
An open site is most suitable, or as open as you can manage; keep 10m (30ft) from any substantial trees if at all possible. This is not only because of the shade they might cast, but also because they shed leaves and twigs, which can cause damage and will certainly block gutters and increase the frequency with which you have to clean the glass. Some trees, particularly limes, are hosts to pests that drop sticky honeydew onto whatever is below them; this encourages moulds to grow — again, something to be avoided if possible.

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