How to Grow Grapes in a Greenhouse Guide

How to Grow Grapes in a Greenhouse

Growing grapes in a greenhouse is a rewarding experience that can yield delicious fruit even in cooler climates. The controlled environment of a greenhouse provides ideal conditions for grape cultivation, allowing for better temperature management, protection from pests, and extended growing seasons. Whether you're a seasoned gardener or a curious beginner, this guide will walk you through the process of cultivating grapes under glass.

Cultivation Tips

Successful grape cultivation in a greenhouse requires attention to several key factors:

• Ensure proper ventilation to prevent fungal diseases
• Maintain consistent watering and feeding schedules
• Prune regularly to control growth and improve fruit yield
• Monitor for pests and diseases closely
• Provide adequate support for the vines as they grow

Remember, growing grapes is similar to growing strawberries in a greenhouse in terms of care and attention needed, but with some unique requirements.

Site and soil preparation

Proper site and soil preparation is crucial for successful grape cultivation. Choose a sunny location within your greenhouse, ideally with southern exposure. Test your soil and amend as necessary to achieve a slightly acidic pH between 6.0 and 6.5. Incorporate organic matter like compost to improve soil structure and fertility. Ensure good drainage by adding perlite or coarse sand if needed, as grapes dislike waterlogged soil.

Planting

Planting with the roots outside

This method involves creating a small hole in the greenhouse wall and training the vine through it. It allows for natural root spread and reduces watering needs.

Planting with the roots inside

This can lead to earlier fruit production due to warmer soil, but requires more attention to watering and feeding.

Growing grapes in containers

Ideal for smaller greenhouses or if you want to grow multiple varieties. It allows for better control over soil conditions and makes it easier to move plants if needed.

Feeding

Grapes are heavy feeders, especially when grown in a greenhouse. In spring, apply a balanced NPK fertilizer. During summer, switch to a high potassium fertilizer to support fruit development. In autumn, use a low nitrogen, high potassium fertilizer to prepare the plant for dormancy. Avoid feeding during winter when the plant is dormant.

Watering

Consistent watering is crucial for grape cultivation. Water deeply but infrequently to encourage deep root growth. In a greenhouse, you'll need to water more often than outdoor vines. Use a drip irrigation system for efficient watering and to keep foliage dry, as wet leaves can promote disease.

Mulching

Mulching helps retain soil moisture, suppress weeds, and regulate soil temperature. Apply a 5-7cm layer of organic mulch around your grapevines, keeping it away from the stem to prevent rot. Good mulch options include straw, wood chips, compost, and leaf mould.

Growing grapes in containers

Container growing is an excellent option for smaller greenhouses. Choose a large container with good drainage holes. Use a high-quality potting mix designed for fruit trees, and add some slow-release fertilizer. Be prepared to water and feed more frequently than in-ground plants.

Improving yield

Aiding pollination

Gently shake the vines or use a small brush to transfer pollen between flowers during the flowering period.

Thinning dessert grapes

Remove about half of the developing grapes from each bunch to improve the size and quality of the remaining fruits.

Removing tendrils

Cut off tendrils near fruit clusters to direct more energy into fruit development.

Maintaining greenhouse conditions

Sunlight

Grapes need full sun, so position them where they'll receive at least 6-8 hours of direct sunlight daily.

Temperature

Maintain temperatures between 21-26°C (70-80°F) during the day and 15-18°C (60-65°F) at night.

Reduce Heat Loss

Use thermal screens or bubble wrap to reduce heat loss during colder months.

Pruning and training

Proper pruning and training are essential for grape cultivation. The two main systems are the rod and spur system and the Guyot system. For greenhouse grapes, the rod and spur system is often preferred. Prune in late winter when the plant is dormant, removing about 90% of the previous year's growth.

Propagation

Grapevines can be propagated through cuttings or layering. Take hardwood cuttings in late autumn or winter, and plant them in a mix of sand and compost. Keep them in a cool, frost-free place until spring, then plant out in your greenhouse.

Cultivar Selection

Muscat of Alexandria

A classic dessert grape with a rich, musky flavour.

Muscat Hamburg

Also known as Black Hamburg, it produces large, sweet black grapes.

Golden Muscat

A hardy variety with large, golden-yellow grapes.

Canadice

A seedless red grape variety that's great for eating fresh.

Interlaken Seedless

An early-ripening white seedless grape with a sweet flavour.

Problems

Diseases and pests to watch out for

• Powdery mildew: A fungal disease that appears as white powder on leaves
• Grey mould: Can affect fruits, especially in humid conditions
• Red spider mites: Tiny pests that can damage leaves
• Birds: Can be a problem if they find a way into your greenhouse

How To Plant Grapes In A Greenhouse

When planting grapes in a greenhouse, dig a hole for the roots of the vine, ensuring the soil is well fertilised. The hole should be the same depth as the pot you're transferring the vines from. Gently tease the roots out with your fingers as you plant it, as this will encourage the roots to spread out and grow.

Grape varieties to choose for a greenhouse

Some popular greenhouse grape varieties include Thompson Seedless, Black Hamburg, Black Muscat, Flame Seedless, Gros Colman, Regent, and Chasselas. Consider factors such as your greenhouse size, local climate, and personal taste preferences when selecting varieties.

Caring For Grapes In a Greenhouse

Regular care is essential for healthy grape growth. Water the grapevines every seven to ten days during the growing season. Apply a balanced fertilizer in spring and switch to a high-potassium feed as fruits develop. Prune regularly to maintain shape and encourage fruit production.

How to plant grapevines in a greenhouse

Choose a spot at the far end of the greenhouse from the main door to avoid blocking access. Prepare the soil by adding well-rotted compost or fertiliser. Plant the vine at the same depth it was in its nursery container, ensuring the graft union (if present) is above soil level.

How to care for grapevines in a greenhouse

Regular watering, feeding, and pruning are key to caring for grapevines. Monitor for pests and diseases, taking prompt action if any issues arise. Ensure good ventilation to prevent fungal diseases, especially in humid conditions. During the growing season, thin fruit clusters to improve the size and quality of remaining grapes.

How to train and prune grapevines in a greenhouse

Start training young vines by tying the main stem to a support, encouraging upward growth. As the vine grows, select strong side shoots to train horizontally along wires or trellis. Prune in late winter when the plant is dormant, removing about 90% of the previous year's growth. This encourages new growth and better fruit production.

When and how to harvest grapes

Grapes are typically ready for harvest 3-4 months after flowering. Look for signs of ripeness such as full colour development, slight softness when gently squeezed, and sweet taste when sampled. Use clean, sharp secateurs to cut whole bunches, handling them gently to avoid bruising.

Best grape varieties to grow in a greenhouse

Some of the best grape varieties for greenhouse cultivation include:

• Thompson Seedless: A popular green seedless variety
• Black Hamburg: Produces large, sweet black grapes
• Flame Seedless: A red seedless variety with excellent flavour
• Muscat of Alexandria: Known for its rich, musky flavour
• Boskoop Glory: A reliable and hardy variety

Grape Growth Temperature and Humidity Management Chart

Growing grapes in a greenhouse can be a rewarding experience, providing you with delicious fruit and a beautiful addition to your greenhouse. It's a great way to expand your home fruit growing repertoire. With proper care and attention, you can enjoy bountiful harvests of sweet, homegrown grapes.

For more ideas on what to grow alongside your grapes, check out our What to grow in a Greenhouse Beginners Guide.

FAQ

Can grapes be grown in a greenhouse?

Yes, grapes can be grown successfully in a greenhouse. In fact, greenhouse cultivation often leads to better yields and fruit quality, especially in cooler climates.

How long do grapes take to grow?

Grapevines typically take 3 years to produce their first harvestable crop. Once established, they will fruit annually, with grapes usually ready for harvest 3-4 months after flowering.

What compost is best for grape vines?

A well-draining, slightly acidic compost is best for grapevines. A mix of loam-based compost, well-rotted manure, and some grit or perlite for drainage works well. Aim for a pH between 6.0 and 6.5.

Are grapes hard to grow?

While grapes require regular care and attention, they are not particularly difficult to grow, especially in a greenhouse environment. With proper pruning, watering, and pest management, most gardeners can successfully grow grapes.

How to Control Pests and Diseases?

Regular inspection, good hygiene, and proper ventilation are key to pest and disease control. For specific issues, use appropriate organic or chemical treatments as needed. Pruning to improve air circulation can also help prevent fungal diseases.

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