how to grow grapes in britain
There were only three entries for the glasshouse grapes at this year's RHS autumn show; the competitors were two dukes and a Ms M. Walshaw. The Duke of Marlborough went home empty-handed, Ms Walshaw bagged a First for a single bunch and the Duke of Devonshire won top prize for the pair with two bunches of his Chatsworth-grown 'Muscat of Alexandria'.
The lack of take-up for this particular class is not surprising. Growing muscats is a huge achievement and represents months of work, love and worry. They're expensive to produce, but one must remember that these are unbelievably luscious fruit, halfway to a plum, each grape so fat and full you feel it needs a bra. Each one a pure liquid sugar capsule. More of us with greenhouses should at least have a go.
To win competitions you need huge bunches with broad shoulders; every grape must be in good condition, no blemishes, no bruises, and the bloom – the smokiness that covers the skin – must be perfectly intact.
The grapes at Chatsworth are managed by garden custodian Ian Webster, who walks through the grape-houses most days. The thought of all the work he does is inspiring but leaves me feeling faintly exhausted. I ask Ian how much of his technique applies to those of us who grow more usual varieties such as 'Black Hamburg' or even the garden-centre variety 'Italia', which I have in my greenhouse.
If you want perfection, he says, all of his expertise can be applied to home-grown grapes – but you won't need to use any heat.
The grape year
Ian starts the grape year in early January, opening up all the doors and vents of the vinery to "let the cold pour in".
The gardeners have to remove the top 2in of soil from the raised beds every winter to refresh it. The soil is then pH-tested and lime is spread in areas that fall below 6.5. Ideal grape growing soil is between pH 6.5 and 6.7.
The soil is replaced by a mix of about two-thirds loam and one-third sharp sand (no peat) with some charcoal added to keep the soil sweet. This is spread over the beds and lightly watered in. After a week it is top-dressed with blood, fish and bone and again lightly watered.
So, with the doors open day and night, Ian then chooses the coldest day to prune the vines. If done in too mild a spell, the cut wood bleeds and weakens the plants. All new growth is reduced back to usually one bud per spur (which gives you bigger bunches), or sometimes two buds, with all others entirely removed and the spurs tied in firmly, using Flexi-Tie.
Next, Ian – using a blunt knife – scrapes all the loose bark from the main vine stems and around the spurs. This does two things – it gets rid of overwintering pests and, by loosening the bark around the spurs, allows the new shoots to grow through more easily in the spring. The whole place then has a massive spring clean, with every pane of glass, every metal strut, scrubbed down with Jeyes Fluid. With grapes and all their potential pests and fungal diseases, you have to be scrupulously clean.
Turn up the heat
There is then a pause until March, when heat is turned on in one of the houses to bring the grapes into harvest earlier than is natural. The temperature is brought up gradually (to 65C) and the floor damped down, increasing the humidity and creating a perfect microclimate to force fruit for the middle of August. By doing this in one house and not the other, the fruit then comes in succession. Ian closes all the ventilators and keeps the doors closed, ventilating only on the very hottest days. Any draughts on new growth can spell disaster.
Fit to be tied
When the growth reaches 6in, raffia ties are spaced 6in apart between the support wires. The growth is thinned down to one shoot (or sometimes two per spur) and these laterals are tied to the raffia. Without this, the new growth naturally reaches towards the glass and will be scorched.
A swell time
The vines start to flower in mid April – the whole glasshouse fills with a sweet honey scent – and Ian needs to ensure that every truss gets good pollination. He walks down the vines and "taps the rods" to distribute the pollen, doing so every day for a week while they're flowering.
Once the berries are set, they swell very quickly to the size of a pea – and must then be thinned. At least half of the berries in every bunch are taken out with scissors to allow the others to develop.
That's one heck of a job, but has to be done for fat and healthy fruit and it also helps to reduce the chances of powdery mildew. And at least half the total number of bunches are removed altogether to prevent the vine from becoming exhausted. Ian says that if you fail to do this, the plant will take a while to recover.
You also need to stop the new growth at least two leaves behind the bunch – and keep stopping them in the next few weeks. Any young shoots coming in the axils below the bunch should be removed, too. This encourages all the goodness into the one bunch per spur.
Keep your eyes peeled
As the season goes on, ventilation is increased. At this point you have to watch your fruit like a hawk "walking the crop over" – keeping your eyes peeled for the greyish dust on a berry with powdery mildew, or the cobwebs of red spider mite, or cotton wool on any joints of mealy bug.
At Chatsworth they use sulphur vapour to prevent the outbreak of fungal diseases and biological control for the likely pests in a greenhouse. Good old-fashioned jam pots – with a drop of water added – keep the wasps at bay.
Finally, the grapes swell and begin to colour in August, when Ian floods the beds with water and then covers them with white polythene.
This holds the moisture in the soil but also stops the damp rising into the fruit and encouraging botrytis. There is no water on the beds from that moment until the following spring.
In the later-cropping house, the beds are covered with reflective silver sheets, which throws any light up on to the fruit and gives the grapes more colour.
Tips for growing grapes at home
- Ian recommends three varieties for growing at home: 'Black Hamburg', 'Mrs Pince' (a black variety) and 'Foster's Seedling White'
- Grapes are hungry plants so feed regularly with a balanced feed such as blood, fish and bone every six weeks or a liquid feed (such as seaweed fertiliser) every three weeks
- Beware of extreme fluctuation in temperature – try to keep it constant by regulating ventilation
- Remember to renew any string ties that are tying up the rods every year
- Pollinate around midday when the atmosphere is dry
- When thinning, do not touch the grapes, use a small stick with a V notch in the end to steady them, and small pointed scissors
- Do not walk on the vine root area, this can cause compaction and damage the crop
- Never spray the foliage or grapes with water during the growing season
- A neglected vine can be restored with heavy pruning, but only in the depths of winter when it is very cold
- Always try to have the greenhouse floor dry in the evening and overnight
- Clean up shoots and prunings after thinning and de-shooting in summer or they will spread disease