How to Grow Cucumbers in Australia

Cucumber (Cucumis sativus) is a frost-tender annual vine in the gourd family, Cucurbitaceae, grown for fruit picked young and crisp. It suits Australian summers, with two crops a year in the subtropics and a full season in cool gardens. Uneven watering is the usual failure, because it turns fruit bitter and misshapen.

Three mistakes that matter

1. Sowing into cold soil. Seed sown into cold soil often rots, and seedlings set out into cold ground stall. Wait for the soil temperature in When to plant, or start seed in pots no more than four weeks ahead.
2. Letting the soil dry out. Water stress makes fruit bitter, curved and hollow, and flowers drop. Give plants about 25 mm a week from rain and hose together, more in heat, under straw mulch.
3. Leaving fruit to fatten. A fruit left to swell and yellow holds the plant back, and fewer new fruit set. Pick every two to three days at eating size.

When to plant

Cucumber seed germinates in soil between 16°C and 35°C. Sow direct into warm soil, or start seed in pots so plants go out with the taproot undisturbed. A second batch sown in January can keep fruit coming into autumn.

At the cold edge of the window, a seedling heat mat gives pots the 21°C that seed prefers. At the hot edge, shadecloth over the trellis carries plants through an Alice Springs or Perth heatwave.

Site, soil and setup

Cucumbers want full sun, shelter from wind, and rich, free-draining soil that never dries right out. Their roots run close to the surface, so fix the trellis before sowing rather than driving stakes through them later.

Fresh manure burns young roots, and old cucurbit vines carry gummy stem blight (Stagonosporopsis cucurbitacearum) into the next season, so rotate beds.

Container growing

One plant needs a pot at least 40 cm across, holding about 28 L, with a trellis or tripod fixed in it. Fill it with premium potting mix blended with compost. Bush types suit pots best: 'Spacemaster' keeps its vines under 1 m and 'Richmond Green' stays fairly compact.

• Water: daily in summer heat, until it runs from the base.
• Feed: fish and seaweed blend at 25 mL per 9 L fortnightly, then liquid potash per label fortnightly from the first flowers.
• Position: full sun out of the wind, where the vine can climb rather than trail.

Sowing Seeds

Sow direct once the soil is warm, or start in pots where spring is slow or slugs are thick.

Sowing direct

• Sow 10 to 20 mm deep, two or three seeds to a station.
• On a trellis, space stations 30 to 40 cm apart; on the ground, 40 to 60 cm apart in rows 1.2 to 1.5 m apart.
• Keep the surface moist; seedlings show in 4 to 10 days, then thin each station to the strongest.
• Mulch with 5 to 7 cm of straw once the soil is warm, clear of the stems.

Starting in pots

• Sow one seed per small pot and keep it warm, as in When to plant.
• Plant out 3 to 4 weeks after sowing, once nights are warm, without breaking the root ball.
• Harden off (accustom seedlings to sun and wind over about a week) before planting at the spacing above.

Pollination

Cucumbers carry separate male and female flowers on one plant, and bees move the pollen. Male flowers open first on thin stalks, often 10 to 20 before the first female, which sits on a tiny fruit. Flowers without fruit in the first weeks are normal, and cold, wet or cloudy weather keeps bees home.

Gynoecious (all-female) F1 types set more fruit, but those that need pollen often come with a few seeds of a standard variety. Parthenocarpic types set seedless fruit without pollination, which suits greenhouses and insect netting. Where bees are scarce, pollinate by hand in the morning, before the female flowers close.

• Pick a freshly opened male flower and strip its petals to expose the pollen-coated centre.
• Press it into the centre of each open female flower; one male can serve several females.

Care by growth stage

Water and potassium decide this crop. Weeks count from sowing.

That 25 mm is 25 L per square metre; sandy soils take less at a time, more often. If you prefer a conventional feed, use each at its label rate. Mix a controlled release granular (NPK around 14-5-10) into the bed at planting. Water on an all-purpose soluble (NPK around 23-4-18) fortnightly while vines grow. From the first flowers, switch to a fruiting and flowering soluble (NPK around 15-4-26) fortnightly.

Pruning and Training

A trellised vine takes less room, leaves dry fast so mildew spreads slower, and fruit hangs straight and clean. Tie the young stem loosely to the trellis until the tendrils take hold.

• Standard vines ('Marketmore', 'Lemon', Lebanese types): pinch the tip after 5 to 7 leaves, since these fruit on laterals (side shoots), not the leader.
• Laterals: pinch two leaves past a female flower; remove any lateral reaching 8 to 10 leaves without one.
• Parthenocarpic hybrids: train to a single leader like a tomato, removing side shoots, because they flower at each leaf joint on the main stem.
• Bush types such as 'Spacemaster': no pruning and no trellis.

Companion planting

Good partners feed the insects that protect cucumbers, or lend shade and support.

Grows well with

• Dill and coriander left to flower, whose umbels feed hoverflies, and hoverfly larvae eat aphids.
• Nasturtium, a trap crop that draws aphids off the vines; squash the colonies it collects.
• Sweet corn or sunflower on the western side, a living stake and afternoon shade.

Keep apart

• Potato, which hosts the same 28-spotted ladybird.
• Pumpkin and zucchini, which share cucumber fly (Zeugodacus cucumis), both mildews and mosaic virus, and swamp a bed.
• Tomato, another host of cucumber fly and cucumber mosaic virus.

Harvesting Fruit

Pick from 8 to 10 weeks after sowing, while the skin is glossy and firm and before the seeds harden. Lebanese types are ready at 10 to 12 cm, gherkins at 5 to 6 cm and slicing types at 15 to 20 cm. Apple types are picked at tennis-ball size.

• Cut the stalk with secateurs; pulling tears the vine and the fruit.
• Remove any fruit that has yellowed or swollen, so the plant keeps setting.

Cucumbers keep 10 to 14 days at 10 to 12°C, in a cool room. Colder than that for more than two or three days, they pit and turn watery. Bananas and tomatoes stored nearby turn them yellow.

Eat them fresh, pickle the small ones, or grate them into tzatziki. Pickle only to a tested recipe, such as the National Center for Home Food Preservation's; too little acid lets botulism grow.

Common problems

Bitter fruit. Cucurbitacin, the bitter compound, rises when plants are stressed by heat, drought, uneven watering or poor soil. It sits mostly under the skin and towards the stem end, so peel and trim a mildly bitter fruit, and discard one that stays bitter. Nearby pumpkins or melons are not the cause, since they cannot cross with cucumbers. Burpless types carry little of it.

Flowers but no fruit. Small fruit that yellow and drop were never fertilised; see Pollination.

Curved, tapered or hollow fruit. Poor pollination, or a dry spell while the fruit filled; keep water steady and hand-pollinate when bees are scarce.

Leaves wilting on hot afternoons. Heat and dry soil; water deeply in the morning, and see When to plant for shade.

Pests and diseases

Cucumbers share their pests and diseases with pumpkin, zucchini and melon.

Cucumber fly (Zeugodacus cucumis). Native to Queensland, the Northern Territory and northern New South Wales, and a major pest of cucurbits there. Maggots tunnel through young fruit, which rots or drops. Net or bag fruit once pollinated, pick often, and freeze stung fruit for two days or boil it rather than composting it. It ignores the male lures in Queensland fruit fly (Bactrocera tryoni) traps, and cucumber is not on that fly's host lists. Read more

28-spotted ladybird (Epilachna vigintioctopunctata). Dull orange, 7 to 10 mm, with 28 black spots and a fine downy coat, unlike the glossy beneficial ladybirds. Adults chew holes and the yellow, spiny larvae graze leaf undersides; squash both, and the yellow egg clusters under leaves.

Green peach aphid (Myzus persicae) and melon aphid (Aphis gossypii). Both suck sap from shoot tips, but their real damage is the virus they carry. Hose small colonies off or use insecticidal soap, and pull sowthistle and nightshade, which host both. Read more

Cucumber mosaic virus (CMV). An aphid picks it up in under a minute and spreads it for a few hours, so no spray stops it. Infected plants stunt, with mottled, curled leaves and small, distorted fruit; pull and bin them, wash hands and secateurs, and grow resistant varieties like 'Marketmore'. Read more

Powdery mildew (Podosphaera xanthii). White powder on the older, shaded leaves first, spreading in warm weather whether leaves are wet or not. Cut out the worst leaves and spray 1 part full-cream milk to 10 parts water in the morning, repeating after rain. Resistant types include 'Marketmore' and 'Burpless Tasty Green F1'. Read more

Downy mildew (Pseudoperonospora cubensis). Angular yellow patches boxed in by the leaf veins, with grey-purple fuzz beneath on damp mornings. It thrives on 6 to 12 hours of wet leaf, so it follows rain and evening sprinklers. Thin the canopy and remove affected leaves; a copper fungicide registered for cucurbits protects new growth in a wet spell. Read more

Prevention first

• Grow on a trellis with space between plants, so leaves dry by mid-morning.
• Keep netting clear of the fruit, since fruit fly can sting through it.
• Turn leaves every few days for ladybird eggs, aphids and the first mildew spots.
• Bin spent vines and treated stung fruit rather than composting them.

Tips

1. Where cucumber fly is bad, grow a parthenocarpic type under fine insect mesh from planting, since it sets fruit without bees.
2. To save seed, use an open-pollinated variety such as 'Marketmore', since F1 seed does not come true, and leave a fruit until yellow and soft. Bag and hand-pollinate its flowers if other varieties grow nearby. Soak the scooped seed for 2 to 4 days, skim the pulp and dry the seed that sinks.
3. African Horned cucumber (Cucumis metuliferus) is a different species, a scrambling annual to 2.5 m whose horned fruit ripens golden yellow.