The Grapevine Bonsai: The Charm of Miniature Bunches

The common grapevine (Vitis vinifera) is a bonsai with an ancient charm, deeply tied to our culture and our landscapes. It is an extremely vigorous deciduous climber that over time develops a twisted, massive trunk covered with fibrous bark that peels away in strips. In a pot it gives great satisfaction: in spring it buds strongly, in summer it can produce real miniature bunches of grapes, and in autumn its leaves turn spectacular colours, from golden yellow to deep red. The main challenge with the grapevine is controlling its vigour and reducing leaf size.

Origin & species

Native to the Mediterranean basin, the Middle East and Central Asia, the grapevine belongs to the Vitaceae family. In bonsai, besides the classic Vitis vinifera, ornamental vines or related species such as the Virginia creeper or American vine (Parthenocissus) are often grown, much loved for their autumn colours, although they produce inedible berries instead of the classic grapes.

Position and microclimate

The grapevine is a sun-loving plant: it demands full sun.
Strong direct sunlight is the only way to obtain short internodes, reduce the size of the leaves (naturally very large) and ripen the bunches properly.
It likes a well-ventilated position. Air circulation is essential to prevent the classic fungal diseases to which it is very prone (powdery mildew and downy mildew).

Watering

In a pot, the grapevine is a "sponge".
Water generously when the surface of the soil mix starts to dry out. In summer the large leaves transpire a great deal of moisture, so the water requirement is very high: never let it run short of water, especially if the plant is ripening its bunches. A serious lack of water will dry up the fruit and make it drop immediately.

Water quality

Extremely tolerant and hardy.
It accepts tap water well, even hard water. It needs neither acidic soils nor demineralised water.

Substrate

It needs a rich soil but with perfect drainage to avoid rot.

• Recommended mix: 40% pumice, 30% akadama and 30% high quality general purpose soil mix.
• A good organic component is needed to support the vigorous growth and the swelling of the fruit.

Repotting

Repot every 1-2 years for young plants and every 2-3 years for mature specimens.
When: Absolutely at the end of winter (February-March), before the buds swell. If you repot late, when the sap is already moving, the plant will "bleed" copiously from the cut roots and risks being weakened.
Prune the fleshy roots decisively to encourage the production of fine feeder roots.

Fertilising

The grapevine is a "hungry" plant.
Start spring feeding with a balanced organic fertilizer. When the small bunches form, switch to a fertilizer richer in potassium and phosphorus to support the fruit, reducing nitrogen so that the leaves do not become giant.

Flowering and fruiting

The flowers are panicle-shaped inflorescences, insignificant to look at but fragrant.
If fruit set is successful, the bunches will form. On a bonsai, a single bunch can absorb enormous energy: if the plant is young or in the training stage, remove the bunches early. If it is mature, leave only 1 or 2 to balance aesthetics with the health of the tree.

Structural pruning

Carried out in midwinter (December-January).
Beware of "vine bleeding": If you prune in late winter/early spring, sap will run from the cuts continuously for days. Prune when the plant is in deep dormancy.
The grapevine suffers from strong sap die-back: when you cut a branch, always leave a long stub above the last bud, because the cut portion of wood will dry out internally. Never cut flush with the trunk!

Maintenance pruning

During the summer the shoots extend enormously (even by metres!).
Let the shoot grow until it has developed 6-7 leaves, then shorten it back to 2 or 3 nodes. This "grow and cut" thickens the base of the branch and densifies the ramification.

Pinching and defoliation

To obtain small leaves, defoliation (partial or total) is often used at the end of May/beginning of June, cutting away the large leaves and leaving the petiole. This will stimulate a second flush of much smaller leaves. Do not defoliate if the plant is producing grapes, otherwise you will halt ripening.

Wiring & bending

Young branches lignify quickly and become brittle.
The wire should be applied to shoots that are still semi-herbaceous or just lignified in summer. As growth is very fast, the wire can bite in within a few weeks. Old branches will not bend without snapping: for those, use only directional pruning and guy wires.

Diseases and pests

Fungal diseases are the real enemy:

• Powdery mildew: White, dusty coating on the leaves. Prevented and treated with sulphur and plenty of ventilation.
• Downy mildew: Translucent oil-spot markings on the upper leaf surface and white mould on the underside. Prevention with copper products (Bordeaux mixture).
• Red spider mite or yellow mite: Causes yellowing and leaf drop in high summer.

Winter & protection

The grapevine is a very hardy plant that tolerates frost well.
It can spend the winter outdoors. Only in the case of very small pots and continuous frosts below -5°C is it advisable to protect the roots by mulching the pot or moving it into a cold greenhouse.

Yearly calendar

• December-January: Structural pruning (to avoid "bleeding"), copper treatments.
• February-March: Repotting (compulsory before bud break).
• April-May: Explosive growth, prevention of powdery and downy mildew.
• June-July: Frequent green pruning, defoliation (if needed), plenty of water.
• August: Ripening of the bunches, vegetative rest.
• September-October: Autumn colour, PK fertilizer.
• November: Leaf fall, dormancy.

Useful products for this bonsai

• Sifted pumice (For optimal drainage)
• Hanagokoro organic fertilizer (Slow, balanced feeding)
• Powdery mildew treatment / sulphur (To fight powdery mildew)
• Angled cutter (For cutting vigorous shoots)
• Copper-coloured aluminium wire (To guide young branches)
• cut paste (Essential on every cut to avoid rot and sap loss)

Frequently asked questions about the grapevine

What does "vine bleeding" mean?
In spring, before the buds open, the sap rises from the roots under great pressure. If you prune the plant at this time, liquid sap will flow abundantly from the cuts (it looks as if the plant is weeping), wasting precious energy. For this reason, major pruning is done in midwinter.

Why do my bunches dry up while they are still small?
This often happens if the plant goes thirsty even for just half a very hot day. Another cause can be an attack of microscopic fungi (such as downy mildew) on the stalk of the bunch. Keep watering regular and carry out preventive treatments.

Can I eat the grapes from my bonsai?
Certainly! The grapes produced are identical to those of large vineyards, just on a smaller scale. Naturally, wash the berries well and make sure you have not applied insecticides or fungicides unsuitable for agricultural use in the weeks before harvest.