How to Grow Carrots in Australia

Carrot (Daucus carota subsp. sativus) is a biennial root vegetable in the carrot family, Apiaceae, grown as an annual for its sweet, crisp taproot. It suits almost every Australian garden, and one packet gives months of picking. The usual failure is a row that never comes up, and the cause is nearly always a dry seedbed.

Three mistakes that matter

1. Sowing into fresh manure or rough soil. A root that meets a stone, a clod or a lump of manure forks, twists and grows hairy. Dig at least 25 cm deep, rake out stones and skip the manure: see Site, soil and setup.
2. Letting the row dry out. Carrot seed sits near the surface for two to three weeks, and one dry afternoon can end the germination. Soak the bed first, cover the row with a board or damp hessian, and check daily: see Sowing Seeds.
3. Skipping the thinning. Crowded seedlings stay spindly and twist around each other, so none forms a proper root. Thin to 5 cm at the first true leaves and eat the second thinning: see Thinning.

When to plant

Carrot seed germinates in soil from about 8°C to 30°C, quickest between 20°C and 30°C, and it stalls above 35°C. The plants grow best through days of 15°C to 21°C, so aim to finish the crop in mild weather. Sow a short row every two to four weeks, and the picking runs for months.

At the hot edge of the window, choose a quick short type and shade the row until the seedlings show. At the cold edge, wait for soil above 10°C. Growth below that is slow, and six to eight weeks of cold can send plants to flower.

Site, soil and setup

Carrots want full sun, though they still crop on three or four hours of direct sun a day. The taproot decides everything, so the soil must be loose, deep and free of stones. The sandy soils around Perth show why: Western Australia grows most of the country's export carrots on them.

Fresh manure and coarse, half-rotted compost make roots rough, spongy and branched, so anything organic goes in fine, aged and weeks ahead. Carrots are not heavy feeders and do well in the bed a manured crop has just left.

Container growing

A pot at least 30 cm wide and 30 cm deep, about 13 L, grows a worthwhile crop of short carrots. Fill it with a potting mix made for vegetables, never garden soil. Choose a light-coloured pot for warm-season sowings, and 'Paris Market', 'Little Finger' or 'Baby Amsterdam' for the seed.

• Water daily in warm weather until the seedlings are up, then whenever the top few centimetres are dry. A pot that dries out and floods again splits roots.
• Feed seaweed solution at half strength, 15 mL per 9 L, fortnightly from the first true leaves. As roots swell, switch to fish and seaweed blend at 25 mL per 9 L fortnightly. Or mix a controlled release granular (NPK around 14-5-10) into the mix at sowing and add nothing more.
• Full sun in the cool months; morning sun only once summer heat arrives.

Sowing Seeds

Sow direct, because a moved seedling forks, and keep the top centimetre damp until the grass-like seedlings show.

Sowing direct

• Soak the bed the day before, then draw a furrow 5 to 10 mm deep, with rows 25 to 30 cm apart. On clay, fill it with sieved compost or seed-raising mix.
• Mix the seed with four to ten parts of dry sand and dribble it along the row, roughly a seed a centimetre. Cover lightly and press the soil down with a board.
• Lay the board or damp hessian over the row and lift it daily to check the moisture. Remove it the day the first seedlings appear.
• Expect seedlings in 10 to 21 days, sooner in warm soil. The first leaves look like grass, so mark the row with a few radish seeds.

Seed keeps for a few years in a cool, dry drawer, but old seed germinates thinly.

Care by growth stage

Even water and restraint with nitrogen decide this crop. Weeks count from sowing and suit a Nantes type; baby carrots run ahead and long types behind.

Those water figures suit open beds in dry weather; rain and mulch cut them. Hold the nitrogen: high-nitrogen feeds such as fish emulsion grow big, bushy tops and do nothing for the roots.

Thinning

Thinning gives each root its 5 cm, and it is done twice: at the first true leaves, then at 12 to 15 cm tall. A crowded row grows thin, twisted roots whatever the soil.

• Thin after watering, when the soil is soft and the seedlings lift cleanly.
• Snip or pinch the extras at soil level rather than pulling, so the keepers stay put.
• Leave one plant every 5 cm for baby and round types. Widen long types to 10 cm as you pull the second thinning to eat.
• Firm the soil back around the keepers, water them in, and take the thinnings away.

Companion planting

Carrots are low, slow and lightly fed, so the best neighbours leave early or cast no shade.

Grows well with

• Lettuce, which is picked before the carrots need the space.
• Radish, the row marker, pulled before the carrots thicken.
• Spring onions and leeks, upright and shallow, which cast no shade.
• Dwarf beans and peas, which fix their own nitrogen and leave a lightly fed bed behind them.

Keep apart

• Parsnip, parsley and dill, which share carrot's leaf blight (Alternaria dauci) and other carrot-family troubles.
• Tomato, capsicum, potato and pumpkin as the crop before carrots on warm, sandy ground, because all build up root-knot nematode (Meloidogyne species).
• Brassicas, whose broad leaves shade a low row and whose beds are fed harder than carrots like.

Harvesting Roots

Pull the first roots when the shoulders reach 2 to 3.5 cm across, usually 9 to 18 weeks from sowing depending on the type.

• Water the bed a couple of hours before lifting, so the roots come out whole.
• Loosen alongside the row with a fork on heavy soil, pull the largest first and leave the rest to grow on.
• Twist or cut the tops off straight away, because they draw moisture from the root.
• Lift the row before roots turn woody, at about 16 to 18 weeks for most types.
• In cool districts, leave winter roots in the ground and pull as needed, but lift before spring growth restarts.

Store topped, unwashed roots in a sealed bag in the coldest part of the fridge, close to 0°C, where they keep for weeks. Keep them away from apples, pears and other ripening fruit, whose ethylene turns carrots bitter; bunched carrots with tops on last about ten days. Eat them raw, roasted, grated, juiced or pickled; purple and red types keep their colour when cooked.

Common problems

Split or cracked roots. Soil that dried right out and was then flooded, or a heavily fed bed, cracks roots lengthways; water evenly and mulch. Forked roots are the fault in Three mistakes.

Green shoulders. Light on a crown that has pushed above the soil turns it green; hill soil or mulch over shoulders as they show.

Bolting. Cold spells (see When to plant) then lengthening spring days make a young carrot bolt (run to flower), and the root goes woody. Sow after the coldest weeks and pull any plant that throws a stalk.

Woody or bitter roots. Long spells above 25°C give roots a strong, harsh flavour, and roots left too long turn starchy: see Harvesting Roots for the lifting time.

Pale, slow roots. Below 10°C growth stalls and roots come long, thin and pale, because colour develops best between 10°C and 20°C; winter rows simply need more weeks.

Pests and diseases

The carrot fly (Psila rosae) of overseas gardening books is not established in Australia; the pests that matter here are below. Read more

Root-knot nematode (Meloidogyne species). Microscopic soil worms enter near the root tip and raise lumps of 1 to 10 mm, so carrots fork, knot and grow hairy. They are common in warm, sandy soils and in Alice Springs backyards. Rotate, add compost, which feeds their predators, and sow for winter, when cool soil slows them. Read more

Green peach aphid (Myzus persicae) and carrot virus Y. This aphid is the most efficient carrier of carrot virus Y, which occurs in most Australian carrot districts. Infected plants show mottled, reddened or feathery leaves, and roots infected young come stubby and knobbly. Pull volunteer carrots and finished rows, the main source of the virus. Read more

Cutworm (Agrotis species). Fat, smooth caterpillars up to 50 mm long hide in the soil by day and cut seedlings off at ground level at night. Picked up, they curl into a C. Clear weeds three to four weeks before sowing and scratch the soil around a felled seedling. Read more

Vegetable weevil (Listroderes difficilis). A flightless grey-brown weevil about 8 mm long with a pale V on its back. Adults and legless larvae feed at night from autumn to spring, notching leaf edges or eating seedlings to the ground. Hunt by torch after dark and clear capeweed, its favourite weed host.

Alternaria leaf blight (Alternaria dauci). Dark brown to black angular spots with yellow halos on the older leaves after wet weather, merging until the tops blacken. Sow thinly so leaves dry quickly, remove spent tops and rotate.

Prevention first

• Rotate carrots and their relatives on a three to four year cycle, off ground that grew nematode-prone crops.
• Cover the row with fine insect mesh from sowing, edges buried, against moths, weevils and aphids alike.
• Weed early and often, since weeds host cutworm and weevil and outgrow a carrot seedling in days.
• Pull volunteer carrots and finished rows, and compost spent tops away from the next sowing.

Tips

1. In the tropics, sow into the dry season. Across Queensland and the north, choose 'Red Kuroda', bred for subtropical and tropical heat, or 'All Seasons', the main Queensland variety.
2. Anzac Day is a fair marker for the last autumn sowing in temperate and Mediterranean gardens; roots sown then fill through the cool months.
3. Leave one or two of your best plants to flower in their second spring. The flat white heads feed hoverflies and parasitic wasps that hunt aphids, and the seed can be saved.