Welcome to Top of the Crops! Today you will learn about growing grapes in a polytunnel. For prosperous grape crops, follow our advice below. Don't forget to check out our blog Polytunnel Gardening for more gardening tips.
Grapes are an increasingly popular crop in the UK. As our climate warms, it is becoming easier to grow them outdoors in more locations. But a polytunnel certainly still makes growing grapes a lot easier for most UK gardeners.
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If you are interested in growing grapes where you live, then of course you will need to decide which type you would like to grow. There are dessert types, and wine grapes, though also some cultivars that can be both.
Grape vines do need plenty of space to grow. But tend them correctly and you can grow them even in more restricted spaces. And can get a worthwhile crop after expending some care and attention. These are great edimental plants which produce a yield and look very attractive too.
To grow grapes successfully, you need to choose the right variety, grow them in the right place with the right conditions, and care for your crop correctly. Read on to find out more.
Grapes need:
Full sun or only a very little light, dappled shade in warm locations.
A location that is as warm and sheltered as possible. Either outside in milder areas, or in a polytunnel or greenhouse.
Well-drained, fertile soil, rich in organic matter, with a pH of between 6.5 and 6.8.
Some kind of support to which they can cling/ be tied as they grow.
They are vigorous, fast-growing vines that will need space to grow in order to meet their full potential.
To grow grapes you will need:
Grapevine or vines.
A suitable growing location (usually in the ground, though potentially in a large container).
A polytunnel or other protection for most grape varieties in most parts of the UK.
A trellis or other support structure.
Facility to provide water for your grapevine.
A garden spade.
Pruning tools.
Organic mulch material and other organic materials for feeding.
Grapevines are best planted in winter or early spring, during the dormant period, when they can be purchased as bare root plants or in pots. Ideally, it is best to plant in around March to prevent any potential problems with winter damage.
If planting in the ground, make sure that the planting area is well prepared – weed free and amended with plenty of organic matter.
The grape vine can be planted inside a polytunnel, or with its roots just outside and its growth directed inside, as is common with greenhouse growing. This is a good idea because it reduces maintenance when the plant can be watered by natural rainfall while providing a more protected and warmer environment for the above ground portions of the plant.
When planting, it is of course important to think about how the vine will be supported as it grows and which pruning and training system you will implement.
Usually, one grape vine will take up a lot of space in a smaller polytunnel. In a larger structure, you may plant more than one but make sure these are at least 1m apart.
Grapes can also potentially be grown in large containers. Choose a container that is as large as possible, with good drainage at the base. It should be at least 35cm wide and deep, filled with John Innes no. 3 or an equivalent.
Specific training can allow grape vines to be grown in smaller spaces, though of course yields won't tend to be as high and maintenance will be more time consuming when it comes to watering etc. when grapes are grown in containers.
Grapes are relatively easy to grow, as long as you have chosen the right location and follow care requirements to the letter. The most important things when it comes to care are placement, watering, feeding, and pruning and training.
Here are the basic things you need to know to care for your grapes and grapevines successfully:
Grapes are fairly drought-tolerant as a rule, and will not typically need a lot of additional watering when they are grown outdoors in the UK. Take note of placement however – sometimes vines may be planted within the rain shadow of a wall or fence and so may require additional watering.
Where they do not get natural rainfall, of course, and during prolonged dry spells, you will need to take things into your own hands. And plants that are just getting established and grown in pots will typically need to be watered more often.
It is a good idea to apply an organic mulch such as homemade compost or well-rotted manure around the base of grapevines upon planting, and to replenish this each late winter or early spring. This adds slow-release fertility, helps to conserve soil moisture, suppresses weed growth to a degree and protects the precious soil ecosystem.
Companion planting can also potentially help grapes to thrive in a polytunnel or elsewhere in your garden.
As well as adding an organic mulch to provide nutrients, grapevines are hungry plants and will also benefit from additional feeding. Add a high potassium general organic fertilizer around the vines in the early spring before growth resumes for the year.
Feed from around a month after growth starts with a high potassium, organic liquid plant feed every couple of weeks or so. You may also increase to feeding once a week once the vine is in full leaf. But stop feeding when grapes begin to ripen as excessive feeding at this time can spoil the way they taste.
Grapes, depending on the variety, will be ready to harvest some time between late summer and late autumn. When ripe they will be at their sweetest, and will have changed to their full, rich colour. Tasting a grape is usually the best way to see if they are ready to harvest. Once they are ripe, cut the bunches from the vine.
Note that you may also harvest leaves from your vines as a secondary yield. These are used in stuffed vine leaves and other recipes.
If you have grown dessert grapes these are best eaten right away. They will keep in your fridge for a couple of weeks.
Wine grapes can be eaten fresh, but since they usually have thicker skins and a more acidic taste, they are usually, as the name suggests, used to make wine.
Propagating grape vines is not an operation usually undertaken by beginners or home gardeners, as it often involves complex grafting processes. They are often propagated by whip and tongue grafting onto a suitable rootstock.
Hardwood cuttings and even softwood or semi-ripe cuttings can also sometimes be successful. But growing from pips is not recommended. The process is slow and the plant will typically produce lower quality fruits than the parent plant.
One of the most important things when caring for grapes is to make sure you understand the basics of pruning and training. Grape vines will need some form of support structure up which to grow, such as a trellis, wire system, or cordon. What is required exactly depends of where you are growing your grapes and which system you choose.
There are a couple of main pruning methods. The first is the Guyot method, the second is the cordon, or rod and spur method. The former is often used in vineyards, outdoors. The latter is typically more useful for polytunnels and greenhouse growers. Also an option in very small spaces is growing a grape vine as a standard, with a lolly pop like shape.
The main pruning is typically carried out in the winter, whichever method is used.
On newly planted grapevines, it is also best to remove all flowers from the vine for the first two years so that the plant can focus on healthy establishment. In the third year, it is best to then only allow three bunches of grapes to grow – then more (usually five or so) in subsequent years.
When growing dessert grapes in a polytunnel, thinning bunches of grapes is a fiddly job, but one that can be worthwhile to improve air circulation and the quality of grapes that remain. Remove around one in three of the grapes from each bunch.
Through the growing season, you may also remove tendrils, or unwanted shoots in order to keep your vines in tip top health. Pruning well throughout the year will increase significantly the size and quality of your grape harvest.
There are numerous cultivars of dessert and wine grapes to choose from that are suited to UK cultivation. Some highly regarded varieties, which have an award of garden merit from the RHS are:
Unfortunately, grapes can be prone to a number of different pest and disease problems. Pests to look out for include birds and wasps, which can get to the fruits before you do and cause a lot of damage.
Fungal diseases that can arise include powdery mildew, grey mould, and downy mildew. Keeping good airflow is key to reducing the chances of these issues taking hold.
Environmental issues due to nutrient deficiencies, lack of water or waterlogging, too little sun, frost damage etc. are also relatively common. Ensure that you place and care for grapes correctly to reduce the chances of any issues.
If grapes are small and disappointing, try reducing the number of bunches you keep, thin the fruits, and prune correctly and you should get bigger, better grapes in future.
Grow with the roots outside or inside the polytunnel, but make sure you remember watering needs will differ depending on your choice. Having the roots outside makes maintenance easier.
Keep on top of ventilation and ensure good airflow throughout the summer.
When growing undercover, pollination may sometimes be patchy with some varieties. Improve pollination by shaking the vines, or by running a cupped hand over each bunch of flowers to transfer some pollen between them.
Consider companion plants for grapes in a polytunnel. Good companions for grapes include aromatic herbs such as rosemary, thyme, hyssop, lavender and sage, for example.
Grapes may not be the easiest crop to grow. But get it right when it comes to placement and care and you should be able to enjoy harvesting grapes from your own garden in increasing quantities over the years to come.
