How to Grow Cress in Australia

Cress is the shared name of three peppery salad plants in the cabbage family, Brassicaceae. They are garden cress (Lepidium sativum), land cress (Barbarea verna) and watercress (Nasturtium officinale). Garden cress can be cut two to three weeks after sowing. Land cress gives weeks of picking, and watercress grows in a pot standing in water. The flowering nasturtium and rocket are separate crops. The usual mistake is sowing cress into summer heat.

Three mistakes that matter

1. Sowing into summer heat. Cress is a cool-season crop, and hot weather sends plants to flower early, after which the leaves lose their flavour. Sow in the cooler months, or give warm-weather sowings shade, as set out in When to plant.
2. Letting the seedbed or pot dry out. Cress seed and its young roots sit in the top few millimetres of soil, so they dry out fast in warm, windy weather. Water lightly every day until plants are growing strongly.
3. Burying or crowding the seed. Fine cress seed holds little stored energy, so seed sown deep may never reach the surface. Seed dropped in clumps stays wet and can rot. Scatter it thinly and barely cover it, as in Sowing Seeds.

When to plant

Cress germinates best in cool soil, about 10°C to 20°C, and grows best through the cooler months. Sow garden cress every week or two for a steady supply; land cress and watercress crop for weeks from one sowing.

At the hot edge of a window, sow in afternoon shade. A tray of garden cress on a bright windowsill grows at any time of year. At the cold edge, start trays indoors and move pots outside once hard frosts pass.

Site, soil and setup

Garden cress and land cress need moist soil that still drains, while watercress grows with its roots in mud or shallow water.

Keep watercress to tubs, ponds and damp garden beds. It already grows wild in waterways across Australia and is a common aquatic weed of lowland creeks and drains in southern Victoria.

Container growing

Use trays and pots with drainage holes. Garden cress needs only a shallow tray holding at least 2 cm of seed-raising mix. Land cress and watercress need a pot about 30 cm across, holding 10 to 15 L of premium potting mix. Stand the watercress pot in a tray or bucket holding 5 to 8 cm of water. For small spaces, 'Extra Curled' and 'Aqua Large Leaved' suit windowsill trays, 'American Upland' a pot, and 'True Water' a pot in water.

• Water: check trays every day, and water pots daily in summer heat. Tip out the watercress tray at least weekly, wipe it inside to remove mosquito eggs, and refill it with fresh water.
• Feed: fish and seaweed blend at 25 mL per 9 L, fortnightly, for land cress and watercress; trays of garden cress need none.
• Position: a bright windowsill for trays; morning sun and afternoon shade for pots outdoors.

Sowing Seeds

Sow cress straight into its bed, tray or pot; only watercress is worth raising first in small pots.

Choosing a type

Sowing garden cress

• In trays, scatter seed thinly over damp seed-raising mix and press it in without covering it.
• In the garden, sow in rows 7 to 10 cm apart and cover lightly, no deeper than 5 mm.
• Keep the surface damp; seedlings emerge in 2 to 7 days.

Sowing land cress and watercress

Both have small seed and a slower start, so sow a pinch in each spot and thin later, as in Thinning. Watercress seedlings raised indoors need hardening off (getting used to sun and wind over about a week) before they go outside.

• Land cress: sow about 5 mm deep in rows 30 cm apart; seedlings emerge in 7 to 14 days.
• Watercress: sow on wet mix in small pots and barely cover, 1 to 2 mm deep; seedlings show in 5 to 14 days.
• Stand watercress pots in a saucer of water from the day of sowing.
• Plant watercress out at about 5 cm tall, 15 to 20 cm apart, into a wet bed or a pot in water.

Care by growth stage

Steady moisture and cool weather decide how long cress keeps cropping. Weeks count from sowing.

If land cress or watercress stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10) can help. Scratch it in at label rate. In hot spells, move trays and watercress pots into shade, which can lengthen the cropping season.

Thinning

Thin land cress and watercress once seedlings have their first true leaves, so the plants you keep grow broad rosettes and strong stems. Garden cress that will be cut as seedlings needs no thinning.

• Snip unwanted seedlings at soil level with scissors, so the roots you keep stay undisturbed.
• Eat the thinnings in salads.
• Pinch out flower stems on land cress and watercress as they appear.
• Cut leggy watercress back to about 10 cm and let it regrow.
• Pull garden cress once it flowers and sow again.

Companion planting

Good neighbours give cress summer shade or confuse the cabbage white butterfly.

Grows well with

• Dill and coriander, whose strong scent helps confuse egg-laying cabbage white butterflies.
• Lettuce, which suits the same cool, moist bed and is not a cabbage white host.
• Tall amaranth or tomatoes on the sunny side, for afternoon shade in warm months.

Keep apart

• Cabbage, broccoli and kale, which share cabbage white caterpillars and aphids.
• Rocket and mustard, cabbage-family salad crops with the same pests.
• Land cress beside brassicas; grown at the far end of the garden, it lures egg-laying cabbage whites away from them. Pull and bin it once caterpillars build up, as they survive on it.

Harvesting Leaves

Cut garden cress with scissors when seedlings reach 5 to 8 cm, usually 2 to 3 weeks after sowing. Pick land cress once plants are established and about 10 cm high, and watercress from the age given in Choosing a type. Keep picking both before they flower.

• Cut garden cress seedlings in one go, then resow; a second cut is rarely worth the wait.
• Take the outer leaves of land cress with scissors and leave the centre to regrow.
• Snip watercress stems above a leaf joint, and the plant branches and regrows.
• Rinse all cress well before eating.

Cress is best eaten the day it is cut. Watercress keeps for about a week, washed and bagged in the fridge crisper. Eat cress raw in salads and sandwiches, or stir it through soup at the end of cooking.

Do not eat raw watercress picked from creeks. Water in grazing country can carry liver fluke (Fasciola hepatica), a parasite of sheep and cattle that occasionally infects people. Cress sprouted in a jar is a separate job. Like all raw sprouts, it can carry E. coli, Listeria and Salmonella, and even strict hygiene cannot make sprouts bacteria free. Tray-grown seedlings carry less risk, but people with lower immunity should avoid eating either raw.

Common problems

Plants flowering within weeks. Heat and dry soil push cress to flower early, and the leaves lose flavour; see Three mistakes, then resow in a cooler, shadier spot.

Tall, pale, floppy seedlings. Trays kept in too little light stretch towards the window; move the next tray to the brightest sill. Read more

Seedlings bunched in patches. Cress seed turns sticky once wet and clings together; mix it with dry sand before scattering. Read more

Slimy water and rotting stems. Stale, stagnant water around watercress roots lets them rot; change it as in Container growing.

Yellowing between the veins of new watercress leaves. Often iron shortage, most common in winter; confirm it, then apply a soluble trace element mix at label rate.

Pests and diseases

Cress shares the pests of cabbage and broccoli. Use only sprays labelled for the pest on leafy vegetables, and keep to any withholding period before picking.

Common garden snail (Cornu aspersum) and slugs. They feed at night and after rain, chewing seedlings and soft watercress leaves. Pick them off by torchlight and set beer traps among the plants. Read more

Cabbage white butterfly (Pieris rapae). Its blue-green caterpillars chew holes in watercress and land cress leaves. Cover plants with fine mesh and pick caterpillars off by hand. Read more

Cabbage aphid (Brevicoryne brassicae) and other aphids. Small sap-suckers cluster on shoot tips and leaf undersides, most often on watercress and land cress. Knock them off with a strong jet of water, or spray insecticidal soap under the leaves. Read more

Whitefly (Aleyrodidae). Tiny white insects rise from the undersides of watercress leaves in warm weather. Spray insecticidal soap under the leaves. Read more

Damping off (Pythium species and Rhizoctonia solani). Seed rots before it emerges, or seedlings collapse at soil level, most often in thick, wet trays. Thin crowded seedlings for airflow, and water only enough to keep the surface damp. Read more

Downy mildew (Hyaloperonospora parasitica). A fluffy white mass of spores grows under seed leaves, then black speckling shows above and leaves yellow. It attacks cabbage-family seedlings, watercress among them, most in the cooler months. Pull out badly infected seedlings. Read more

Prevention first

• Use clean trays and fresh seed-raising mix, since damping off spreads in old mix and on dirty tools.
• Check leaf undersides weekly for eggs, caterpillars and aphids.
• Clear logs, rocks and leaf litter from bed edges, where snails shelter.
• Water the mix rather than the leaves, and space trays so air moves between them.

Tips

1. Grow cress heads with children. Pierce a drainage hole in empty eggshells, fill them with seed-raising mix, sprinkle seed on top and cut the green hair in about a week. See growing from seed with kids.
2. Start watercress from stems: stood in a glass of water, they grow roots at the leaf joints and can then be potted up.
3. Sow garden cress between slower crops such as carrots; it is cut long before they need the room.