Zucchini

Light and exposure

The zucchini wants full sun and warmth. Reserve an open spot for it, at least six to eight hours of direct sun a day, sheltered from cold prevailing winds. A corner near a wall that holds the heat suits it well where summers stay cool.

Give it room, because a plant spreads widely, often a square metre or more. A cramped plant is poorly ventilated, and foliage that does not dry quickly after rain catches powdery mildew more easily. Space the plants at least eighty centimetres to a metre apart.

Watering

The zucchini drinks a lot, especially in full production and in hot weather. Water generously and regularly, always at the base and never on the foliage. Foliage wet in the evening, in a damp summer, favours powdery mildew and rots.

A thick mulch at the base keeps the soil cool, limits watering and prevents the soil from splashing the lower leaves with each shower. If the young fruits turn yellow and rot at their tip instead of swelling, it is often a lack of regular water or poor pollination in cool weather.

Soil and repotting

It is a big feeder. It demands a deep, rich soil that holds moisture. Before planting, enrich the hole generously with mature compost or well-rotted manure. An old compost heap in fact makes an ideal growing medium for a zucchini.

The soil must stay cool but well drained, because the roots rot in waterlogged soil. In heavy, damp soil, planting on a small mound improves drainage and warms the roots.

Temperature and humidity

The zucchini only gets going in the warmth and tolerates no frost. It needs warmed soil, at least 12 degrees, to germinate and grow. Below 10 degrees, growth stops and the young plants take a hit.

This is the classic constraint of every temperate climate. Direct sowing in open ground is only feasible once the last frosts have passed and the soil is well warmed, otherwise the seeds rot before emerging. In cool spring weather, pollination goes badly and the first fruits abort, which is normal, production picks up again as soon as the warmth sets in.

Pruning and upkeep

The non-trailing zucchini is not really pruned, but a few old leaves in the centre can be removed during the season to air the heart of the plant and let the sun dry the foliage. It is a useful gesture against powdery mildew at the end of summer.

The real pruning here is the harvest. Pick the zucchini young, between fifteen and twenty centimetres, every two or three days in full season. The more you harvest, the more the plant produces. A forgotten zucchini that becomes a huge fruit exhausts the plant and slows the formation of the next ones.

Pests and diseases

Powdery mildew is the number one enemy of the zucchini in a temperate climate. It is recognised by a white powdery felt on the top of the leaves, appearing above all at the end of the season when the nights turn cool and the humidity rises. It weakens the plant without killing it outright, but reduces the harvest. Air the plants, water at the base and remove the most affected leaves.

Also watch out for slugs, which love the young plants in spring and can level a planting in a single night, as well as grey mould on the flowers and fruits in damp weather. Rot at the tip of young fruits is most often linked to poor pollination in cool weather rather than to a disease.

Propagation

Sowing is simple. Indoors, warm between 20 and 22 degrees, sow in pots four to five weeks before the last expected frost, one seed per pot laid on its edge two centimetres deep. Emergence is quick, often less than a week. Harden off the plants before putting them out.

Direct sowing in open ground is possible once the last frosts have passed, when the soil is well warmed. Sow two or three seeds per station and keep only the most vigorous plant. It is a crop that does not transplant willingly, so handle the root ball with care if you start from pots.

Toxicity

Shop-bought fruits are harmless, but a zucchini with a very bitter taste signals an excess of cucurbitacin, a toxic substance. If a fruit is frankly bitter, do not eat it and throw away the whole plant.

Month-by-month care calendar

Green Hub tips

• A single plant feeds a whole household. Two are amply enough even to give some away, the zucchini produces without counting once it gets going.
• Harvest young and often, every two or three days. A forgotten fruit that becomes a giant exhausts the plant and blocks the next ones.
• At the end of summer, remove the old leaves from the centre to air it and let the sun dry the foliage: it is your best defence against powdery mildew.
• Plant on a small mound enriched with compost. In heavy, damp soil it warms the roots and prevents rot.