General
Cucumber (Cucumis sativus) is a heat-loving annual vegetable grown for crisp fruits. There are three common groups: greenhouse slicing types (often parthenocarpic, long and smooth), outdoor slicing types (shorter, often spined), and pickling/gherkin types (small, firm). They thrive with warmth, abundant organic matter, even moisture, and shelter from wind. Trellising saves space, improves airflow, and yields straighter fruits. Bitter taste is usually due to stress (cold, drought, heat spikes, irregular watering) causing cucurbitacin formation; keep conditions even to avoid this.
Light
Full sun; warm, sheltered position. Greenhouse or polytunnel extends season in all zones.
Soil type
Deep, fertile, well-drained yet moisture-retentive loam enriched with mature compost. Avoid cold, waterlogged soil.
Water requirement
High and steady moisture; never let the root zone dry out. Water at soil level with lukewarm water.
Nutrient requirement
High feeder; needs ample nitrogen early and potassium/magnesium during flowering and fruiting.
Precultivation
Sow indoors 3–4 weeks before planting out. Use 8–10 cm pots, 1 seed per pot, 1.5–2 cm deep, at 22–26°C for quick germination. Provide strong light (south window or 16 h under grow lights) and keep 18–22°C after emergence. Do not overwater; keep evenly moist and well drained. Pot up gently if roots fill the pot—cucumbers dislike root disturbance. Harden off for 7–10 days once nights are reliably above 8–10°C.
Planting
Plant out when nights consistently exceed 10–12°C and risk of frost has passed. For open ground in warm, sheltered beds or under cloche, space 60–90 cm between plants if trellised, 90–120 cm if sprawling. In greenhouse, one plant per 30–40 cm along a bed or grow bag with vertical twine support. Incorporate 3–5 L well-rotted compost per m² plus a balanced organic fertilizer at planting. Mulch immediately (straw, leaf mold, or compost) to stabilize moisture and soil temperature. Train up strings or a trellis; tie loosely and guide the leader as it grows.
Pruning
Greenhouse/parthenocarpic types: Remove lower leaves up to the first 3–4 nodes to improve airflow. Pinch lateral shoots to 1–2 leaves beyond a fruit to balance vigor, and remove yellowing or disease-marked leaves promptly. Outdoor/pickling types generally need little pruning beyond guiding and removing damaged leaves. Avoid heavy pruning in heat waves.
Maintenance
Keep soil evenly moist; water deeply 2–4 times weekly depending on weather, using tepid water. Feed weekly with a potassium-rich organic liquid (e.g., comfrey/nettle tea, seaweed) once flowering begins. Top-dress with compost mid-season. Maintain mulch and ventilate greenhouses daily to reduce humidity and mildew pressure. Monitor for pests; encourage beneficials with companion flowers. Rotate away from cucurbits for 3–4 years.
Harvest
Pick every 1–2 days as fruits size up; harvest in the cool of the morning for best crunch. Greenhouse slicers: 25–35 cm before seeds enlarge. Outdoor slicers: 15–25 cm. Gherkins: 5–10 cm, very firm. Always cut with snips to avoid tearing vines. Remove misshapen or oversized fruits promptly to keep plants setting. Avoid chilling injury—store at 10–13°C and high humidity; use within 3–5 days.
Common issues
Powdery mildew: favors dry leaves and high humidity—ensure airflow, avoid overhead watering, use sulfur/bicarbonate sprays if needed. Downy mildew: cool, humid spells—improve ventilation, use resistant varieties. Cucumber beetles (notable outside Scandinavia) and aphids: use row covers early, release beneficials, wash off aphids. Spider mites in greenhouses during heat: increase humidity, hose undersides, introduce predatory mites. Blossom-end rot–like symptoms usually from irregular moisture and low calcium uptake—keep watering even and mulch well. Bitter fruit: avoid stress, harvest younger.
Rotation schedule
Rotate on a 3–4 year cycle away from all cucurbits (cucumber, squash, pumpkin, melon). Follow heavy feeders with legumes or leafy greens; precede cucumbers with well-manured beds or cover crops like clover or field beans.
Pollination
Varies by cultivar. Parthenocarpic greenhouse cucumbers set fruit without pollination and should be isolated from bee pollination. Outdoor/pickling cucumbers typically require insect pollination.
Companion plants
Dill, nasturtium, marigold (tagetes), calendula, lettuce, bush beans, peas, sweet corn, borage.
Incompatible plants
Potato, fennel, sage/rosemary and other strong aromatic herbs; avoid planting with other cucurbits (pumpkin, squash, melon) to reduce disease carryover.
