How Do I Grow a Grapevine in a Greenhouse or Indoors?

Growing a grapevine in a greenhouse, conservatory, or glasshouse is one of the most reliably successful ways to produce sweet dessert grapes in the UK and northern Europe. The additional warmth and shelter extends the growing season significantly, allows varieties that would fail outdoors to ripen reliably, and eliminates or drastically reduces the main pest and disease pressures. Many Victorian kitchen gardens had a dedicated grape house, and there is good reason to revive the approach.

Planting position — inside or outside the greenhouse

The best approach is to plant the vine outside the greenhouse at the base of the end wall and train the stem in through a small gap at ground level. This gives the vine access to the deep soil and natural rainfall outside while the fruiting canopy is completely under glass. The roots need no watering management beyond the natural soil moisture. Vines planted inside the greenhouse in restricted soil or containers must be watered and fed much more intensively to sustain a large canopy and crop.

Best varieties for greenhouse growing

The classic greenhouse grape for UK gardens is Muscat of Alexandria — a large, amber-skinned, intensely fragrant dessert grape that cannot ripen outdoors in most of Britain. Black Hamburg (also known as Schiava Grossa) is another traditional choice producing large, sweet purple-black grapes. For a slightly cooler or less heated greenhouse, Muscat Bleu and Lakemont (a seedless variety) perform well. Choose varieties specifically listed as suitable for protected growing rather than outdoor varieties, which will be fine but produce lower yields under glass.

Training on horizontal wires under the roof

Fix horizontal wires running the length of the greenhouse at 30 cm intervals under the roof glazing bars. Train the main rod vertically to the ridge, then train horizontal arms along the wires at each level. Fruiting spurs hang their shoots downward or grow upward from the horizontal arms — both work. Ensure the structure can carry the weight of a mature fruiting vine, which can be considerable.

Ventilation — the critical management factor

Adequate ventilation is the most important management challenge in a greenhouse vine. Inadequate airflow leads to powdery mildew, red spider mite, and botrytis as the primary problems. Ventilate freely through summer, opening roof vents and doors on all but the coldest days. During flowering, restrict ventilation slightly to maintain the warmth needed for good fruit set, but return to full ventilation once the berries have set.

Seasonal management through the year

From late winter, keep the greenhouse just frost-free to delay bud burst until frost risk is lower. As shoots extend in spring, tie in regularly and remove surplus growth to maintain the framework. Pinch out tips two leaves beyond the last bunch, remove leaves around the fruit zone from midsummer, and apply a high-potash feed from fruit set through to harvest. After leaf fall in autumn, clean down the glass, scrub the bark with a stiff brush to remove overwintering pest eggs, and apply a dormant lime-sulphur wash to reduce powdery mildew and spider mite overwintering populations.