Cucumbers and cucurbits in hydroponics: varieties that need no pollination, trellising, settings, zucchini and melons

A single well-trained cucumber plant can bear fruit for weeks, while a lettuce is harvested only once. It is the star cucurbit of hydroponics, and the easiest in the family if you choose a variety that does without bees. Zucchini, melons and watermelons take up more room and ask you to play pollinator. Here is how to choose, set up, train, adjust and harvest.

Quick benchmarks are in the cucumber, zucchini, melon and compact watermelon crop guides. Here, we follow the plant from sowing to harvest.

1. The family at a glance

2. Choosing your cucumber

A “parthenocarpic” cucumber sets fruit without pollination. It is the cucumber of commercial hydroponic greenhouses, in two sizes (University of Florida; Auburn University):

Regular garden cucumbers and pickling cucumbers carry male and female flowers and need insects. For containers, NC State University compared many varieties in 12 L (3 gal) tubs: dwarf varieties (Spacemaster, for example) were among the most productive, and three plants per tub yielded more than one or two (Crane, Wehner and Naegele, 2018).

3. The right settings

Heat first. The cucumber is a midsummer plant: on a balcony in Belgium or northern France, set plants out once the nights are mild: a growing medium below 15 °C (59 °F) can be fatal to this summer plant (Penn State). Indoors, a warm spot near a south-facing window works, or a grow light (see the lighting calculator).

Light makes the fruit. In a very bright greenhouse, above 30 mol of light per m² per day, it takes only about ten days from flower to pickable fruit (Auburn University). Under weaker light, everything slows down: allow more time.

4. Which system?

The cucumber grows a big root system and a big plant: it needs a generous volume of water or growing medium and a sturdy support.

• Drip-fed bucket (Dutch bucket): the commercial greenhouse system, with perlite or coco coir. See drip irrigation and Dutch buckets.
• DWC reservoir with an air pump and air stone: very good for one or two plants, as long as the water stays cool and oxygenated. See DWC and oxygen in the nutrient solution.
• Vertical tower: poorly suited, the net cups are too small for such a big plant and the fruits too heavy.
• Kratky: possible for a dwarf plant in a large tub, but the level drops fast once the plant is mature: plan on topping up.

5. Trellising and pruning: the umbrella

1. Tie a string above the plant, to a wire or a sturdy bar, and gently wind it around the stem as it climbs.
2. No fruit at the bottom: remove all small fruits and all suckers on the first 60 to 75 cm (24 to 30 in) (University of Florida), or up to the sixth or seventh true leaf (Auburn University). The plant builds its leaves and roots first.
3. Above that, one fruit per leaf: keep the small fruit in the axil of each leaf, and pinch off every sucker as soon as it appears.
4. At the wire, pinch the tip and let two stems hang down, one on each side, with one fruit per leaf.
5. Remove old lower leaves that are yellow or damaged, to improve airflow.

Regular cucumbers can also sprawl on the ground or on a trellis with lighter pruning, but trellising improves yield and fruit quality (Penn State Extension).

6. Pollinating by hand

Zucchini, melons, watermelons and regular cucumbers have male flowers and female flowers. Without insects, indoors or under insect netting, hand pollination is the only way to get fruit (University of California Riverside).

• Spot the female: a small fruit under the flower. On zucchini, its stem is very short; on cucumber and melon, males come in clusters of three to five and the female is on its own.
• The right time: in the morning, on the day the flower opens. It is receptive for only one day.
• The technique: pick up the yellow pollen from the male with a soft paintbrush, or remove the male’s petals, and dab it onto the center of the female.
• Be patient at first: on cucumber and melon, the first flowers are all male; on hybrid zucchini, they are sometimes female, and they abort because no males are open yet (UC Riverside).

Zucchini without pollination. Parthenocarpic zucchini exist. At Purdue, six varieties, including Cavili, produced more than 2.7 kg (6 lb) per plant in a closed high tunnel, with no insects, with Cavili reaching 3.9 kg (8.6 lb) (Guan, 2020). A serious option for zucchini on a sheltered balcony.

7. Zucchini, melons, watermelons: what changes

8. Calculator: my cucumbers

Enter the number of plants, the type and the sowing date: the calculator gives the space you need, the earliest first harvest and the yield of a plant in top shape. The figures come from well-lit commercial greenhouses: indoors or on a balcony, expect less.

Benchmarks: 0.45 to 0.65 m² (5 to 7 sq ft) per plant; first harvest from 7 weeks after sowing; 0.45 to 1.4 kg (1 to 3 lb) per plant per week at peak, 9 to 11 kg (20 to 24 lb) per plant over 12 weeks of harvest (University of Florida; Auburn University).

9. Step by step: from sowing to the first cucumber

Time: 7 to 10 weeks. Level: intermediate.

1. Sow one seed per rockwool cube or coco coir plug, somewhere warm (see sowing and transplanting). Parthenocarpic cucumber seeds are expensive: no need to sow three per hole.
2. Transplant into the final system once two or three true leaves have formed and roots are coming out of the cube.
3. Set up the string the same day, before the plant flops over.
4. Clean up the bottom every week: fruits and suckers on the first 60 to 75 cm (24 to 30 in).
5. Measure EC and pH twice a week, top up the water every day in hot weather.
6. Pick minis at around 12 to 20 cm (5 to 8 in) and long ones at around 30 to 35 cm (12 to 14 in), with pruning shears, every two or three days at peak.

10. Problems to recognize

11. Common mistakes

12. Key takeaways

Are your cucumbers already climbing, or are your zucchini flowering without fruit? Share your photos on the forum: a photo of the flower is often enough for a diagnosis.