How to Grow Rockmelons in Australia

Rockmelon (Cucumis melo) is a frost-tender annual vine in the family Cucurbitaceae, grown for its sweet, scented fruit. Honeydew, Canary and Piel de Sapo melons belong to the same species and grow the same way. A long, hot Australian summer suits them, and a melon picked ripe at home is far more fragrant than most shop fruit. The mistake most gardeners make is picking too early.

Three mistakes that matter

1. Sowing into cold soil. Seed can then take two weeks to come up, and much of it rots, leaving weak survivors. Wait for the soil temperature in When to plant, or start seed in pots somewhere warm.
2. Feeding too much nitrogen. Rich, leafy feeds make big, bushy vines that set little fruit, and late nitrogen gives soft, split melons. Feed lightly while vines run, switch to potassium at flowering, and stop soon after the fruit set.
3. Picking by size or by the calendar. Almost half of a melon's sugar builds in its last week on the vine, and none is added after picking. Wait for the ripeness signs for each type in Harvesting Fruit.

When to plant

Sow once the last frost has passed and the soil holds 18°C or more at sowing depth. Seed comes up fastest in soil of about 23 to 35°C, usually in 4 to 10 days. The first fruit ripen 10 to 16 weeks from sowing, so sow early in your window.

At the cool edge of a window, start seed in pots under cover and plant out once frost is past. Crops that ripen into cool autumn weather grow slowly and often colour poorly.

Site, soil and setup

Sowing Seeds

Sow into warm mounds where the vines will grow, or start seed in pots where spring is slow.

Sowing direct

• Sow three or four seeds per mound, 10 to 20 mm deep.
• Space mounds 60 cm to 1 m apart, in rows about 1.5 m apart; compact vines such as 'Petit Gris de Rennes' can sit closer.
• Keep the soil moist but not wet until seedlings show.
• At two or three true leaves, snip off all but the strongest seedling at soil level.
• Mice dig up and eat melon seed; where they are a problem, raise seedlings in pots instead.

Some packets hold seed treated with a fungicide, which may be dyed. It is for sowing only, never for eating or feeding to animals. Wear gloves, wash your hands after sowing, and keep treated seed away from children and animals.

Starting in pots

• Sow two or three seeds per biodegradable pot, 4 to 6 weeks before the last frost, keep them warm, and thin to the strongest.
• Harden off (accustom seedlings to sun and wind over about a week) before planting out.
• Plant out when roots fill the pot, usually at the second or third true leaf, without breaking up the root ball.
• Keep the potting mix moist until roots reach the soil, since dry mix shrinks and strands them.

Pollination

Each vine carries male and female flowers, and most melon females hold pollen too. Only a female, with a tiny melon behind its petals, can become fruit. The first flowers are usually male, and males often outnumber females ten to one, so early flowers that drop are normal.

Each flower opens for a single morning, and bees must visit it many times before noon. Poorly pollinated fruit often yellow and fall, or grow flat-sided and misshapen. Hot, dry wind kills pollen, and wet, windy or overcast weather keeps bees from working.

• When bees are scarce, pollinate by hand early in the morning, while the pollen is fresh.
• Pick an open male flower and strip off its petals.
• Dab its pollen onto the centre (stigma) of an open female flower, or carry the pollen across on a soft brush.

Rockmelons, honeydews and the other melons here cross with one another, but not with cucumber, pumpkin or watermelon. A cross does not change this season's fruit; it shows only in plants grown from saved seed.

Care by growth stage

Water and potassium decide the crop: steady moisture from flowering to full size, then less as fruit ripen. Weeks count from sowing direct, and transplants run a little ahead.

Slide a board, tile or thick pad of straw under each young fruit to keep it off damp soil. Water at the base in the morning so the leaves dry before night, which slows mildew.

If you prefer a conventional feed, mix a controlled release granular (NPK around 14-5-10) into the mounds at sowing. Water on an all-purpose soluble (NPK around 23-4-18) fortnightly while the vines run. From the first flowers until fruit reach golf-ball size, switch to a fruiting and flowering soluble (NPK around 15-4-26), all at their label rates.

Companion planting

Melons pair with tall, upright crops, because the vines ramble beneath them.

Grows well with

• Sweet corn, whose tall stalks leave the ground free for the vine to cover as a living mulch.
• Climbing beans, in a three sisters bed where the beans climb the corn and the melon covers the soil.
• Sunflowers, which stand clear above the vines and take little ground.

Keep apart

• Older plantings of pumpkin, zucchini or cucumber, which pass mildew, aphid-borne viruses and pumpkin beetle on to a young crop.
• Tall plantings on the sunny side of the bed, which shade vines that need 6 to 8 hours of sun.

Harvesting Fruit

Most netted rockmelons are ripe when a crack circles the stem and the fruit slips away with gentle pressure.

• Check the vines every day or two once the first fruit colour up, since each vine ripens over two to four weeks.
• On netted types, the tendril nearest the fruit often dries and hardens as it ripens.
• Cut honeydew and winter melons with secateurs, leaving a short stub of stem.
• Pick in the cool of the morning and handle fruit gently, since melons bruise easily.

Netted melons soften a little on the bench, so chill them once ripe and eat them within about a week. Honeydew and winter melons keep for weeks somewhere cool, but cold below 5°C damages honeydew. Store melons away from cucumbers, lettuce and zucchini, since the ethylene gas that ripening melons give off spoils them.

Before cutting, scrub a rockmelon's netted skin under cool running water with a produce brush, and chill cut melon within 2 hours. The NSW Food Authority advises pregnant women and people with low immunity not to eat rockmelon. Eat melons fresh, in fruit salads and smoothies, or freeze chunks for sorbet.

Common problems

Flowers but no fruit. Females fail without enough bee visits, in hot wind, or on overfed vines; see Pollination and Three mistakes that matter.

Bland, pale fruit. Heavy watering in the last week or leaves lost to mildew cut the sugar, as early picking does. Poorly netted fruit is the telltale sign.

Split fruit. Irregular watering or heavy rain as fruit near ripeness makes swelling fruit crack; keep moisture even until the final week.

Rotten patches underneath or bleached tops. Rind lying on wet soil lets rot fungi in, and fruit sunburn when mildew or rough picking strips their leaf cover.

Seedlings collapse at soil level. Damping off fungi thrive in cold, overwatered soil and in fresh, undecomposed organic matter; cutworms can do the same damage. Read more

Vines wilt and stay wilted. Leaves that droop at midday and recover by evening are normal. A vine that stays limp may have dry roots, fusarium wilt or gummy stem blight (Stagonosporopsis cucurbitacearum), which oozes reddish gum from stem cracks.

Pests and diseases

Downy mildew follows warm, wet weather, while powdery mildew and mites build up in dry spells.

Powdery mildew (Podosphaera xanthii). White powder spreads from the older leaves, worst in dry weather and on late crops. At the first spots, spray 1 part full-cream milk to 10 parts water, and repeat after heavy rain. Do not use sulphur, which damages melons. 'Hales Jumbo' and 'Infinite Gold' F1 carry resistance to it. Read more

Downy mildew (Pseudoperonospora cubensis). Yellow spots ringed by a halo appear on the upper leaf, with grey-purple fuzz beneath, in warm, moist weather. Spores need wet leaves, so outbreaks follow dews and rain; use a copper fungicide, as the label directs, on severe ones. Read more

Melon aphid (Aphis gossypii). Colonies of small green to almost black insects cluster under young leaves and shoots. They spread papaya ringspot and zucchini yellow mosaic viruses, which mottle and twist leaves and fruit and cannot be cured. Pull out infected vines, and spray insecticidal soap or horticultural oil at the label rate on the leaf undersides. Read more

Two-spotted mite (Tetranychus urticae). Leaves turn bronzed or mottled yellow, with fine webbing underneath, mostly in hot, dry weather. Predatory mites can keep them in check where sprays are avoided. Read more

Pumpkin beetle (Aulacophora hilaris). Adults are yellow-orange, 6 to 7 mm long, with four large black spots. They chew holes and neat circles in leaves and flowers, and seedlings and fresh transplants suffer most. Catch them early in the morning or at dusk, and grow seedlings fast so they outgrow the damage.

Cucumber fly (Zeugodacus cucumis). This native fruit fly readily infests melons, mostly in tropical Queensland and the Northern Territory, reaching Kununurra and at times the northern NSW coast. Spot a spinosad-based protein bait, as the label directs, on foliage about 1 m above the ground, never on the fruit. Destroy stung and fallen fruit by freezing it or burying it deep. Read more

Prevention first

• Pull out finished vines and fallen fruit straight after the last pick.
• Weed out self-sown pumpkins and wild cucurbits, which can carry viruses into the patch.
• Check the undersides of leaves twice a week from the time runners form.
• Spray only late in the afternoon, after bees have finished, and never use pyrethrum on open flowers.

Tips

1. In cool gardens, start seed on a seedling heat mat, as melon seed needs bottom heat.
2. Note the day each fruit sets. It is usually ready 5 to 7 weeks later, which tells you when to start checking daily.
3. Save seed only from open-pollinated heirlooms grown away from other melons. Seed from F1 hybrids such as 'Infinite Gold' does not come true.