Commercial arugula and rocket production

Commercial arugula production relies on two different species, the annual salad rocket (Eruca vesicaria subsp. sativa) and the perennial wild rocket (Diplotaxis tenuifolia), and serves mainly the fresh leaf and ready-to-eat salad market. Salad rocket gives its first cut from about 20 days and regrows for successive cuts, while wild rocket tolerates more cuts in the same cycle. In Italy, wild rocket accounts for about 50% of the area under leafy vegetables for ready-to-eat salads. The most important technical issue is nitrate, because the EU has set limits for rocket of 7,000 mg/kg in winter and 6,000 mg/kg in summer, and research shows that less nitrogen often gives the same yield. This guide covers the difference between the two species for the market, climate and soil, sowing and density, fertilisation and nitrates, irrigation, crop protection, harvest and shelf life.

Salad or wild rocket

Trait	Salad rocket	Wild rocket
Species	Eruca vesicaria subsp. sativa	Diplotaxis tenuifolia
Cycle	Annual, very fast growth	Perennial, slower establishment
Seed	Larger	Much smaller
Cuts	Fewer, because of early bolting	More successive cuts
Heat	Bolts quickly	More tolerant
Market	Bunches and baby leaf	Mainly baby leaf for ready-to-eat salads, preferred in Italy and Germany

Both species are described in the literature as baby-leaf salad crops of the brassica family, and they are often sold under the same name. Wild rocket was converted from a wild edible plant into a crop only about 25 years ago, and in Italy it is now grown on roughly 4,000 to 4,800 hectares.

Climate and seasons

Arugula is a cool-season crop, with an ideal growing temperature of around 14 to 20°C. The main obstacle to continuous production is early bolting, which appears as day length increases in spring. In Mediterranean regions, the main crops are therefore grown from autumn to spring, in the open field or in unheated greenhouses and tunnels. In Italian trials with wild rocket, marketable yield and mean leaf weight were highest in the winter cycle, compared with the autumn-winter and winter-spring cycles.

Soil

Arugula prefers fertile, well-drained soils rich in organic matter that hold steady moisture, and it is sensitive to soil salinity. To limit soilborne pests and diseases, it does not follow other brassicas, such as cabbage, broccoli or cauliflower, in the rotation.

Sowing and density

Arugula is almost always direct-seeded, because it does not transplant easily, although it germinates and grows very well in plug-tray systems. Density depends on the product:

For baby leaf: very dense sowing in bands about 5 cm wide, at around 2 seeds per centimetre of row, with rows 5 to 15 cm apart
For bunching: thinner sowing, about 1 seed per 2 cm of row, with rows 30 to 45 cm apart
In field trials with wild rocket, densities of 33 to 100 plants per square metre were tested, while in soilless baby-leaf systems densities exceed 1,000 plants per square metre

Because salad rocket grows so fast, growers supplying the market steadily sow in succession, with a new sowing every 2 to 3 weeks.

Fertilisation and nitrates

Rocket, and especially wild rocket, is known for high leaf nitrate levels that can exceed the limits of European legislation. Regulation (EU) No 1258/2011 set two maximum levels for rocket:

7,000 mg/kg fresh weight for produce harvested from 1 October to 31 March
6,000 mg/kg for produce harvested from 1 April to 30 September

Exceeding them is a real risk. In a study of commercial wild rocket crops in southern England, with an average nitrogen application of about 104 kg per hectare, two of the eight crops exceeded the 6,000 mg/kg limit. By contrast, in a trial with wild rocket on sandy soil, 66 to 82 kg of nitrogen per hectare gave the same yield as the conventional rate of 309 kg. Italian studies also show that higher nitrogen rates raise leaf nitrate, and that under water shortage they can even reduce yield.

The practical conclusion is to apply nitrogen with restraint, based on a soil analysis, preferably in small doses, and not shortly before harvest. Rotted manure or compost in the base dressing covers much of the requirement.

Irrigation

Water shortage reduces yield, because both the number and the size of the leaves fall, and it also makes the leaves tough and very hot. Drip or light, frequent irrigation keeps the soil evenly moist. Excess water, on the other hand, causes root rot and favours fungal diseases, especially under cover.

Crop protection

The main pest is flea beetles, small beetles that pepper the leaves with tiny holes and make the produce unmarketable, mainly on young plants. Aphids follow and, in humid conditions, fungal leaf diseases. Prevention rests on insect mesh, rotation, avoiding excess moisture and regular scouting. Every treatment uses only products registered for rocket, after diagnosis by an agronomist, with strict observance of the pre-harvest interval, which in a crop cut every few weeks also sets the spray schedule.

Harvest

Baby leaves are cut at about 10 to 15 cm tall, above the growing point, so the plant regrows for the next cut. In Italian trials, wild rocket gave four to five successive cuts in the same cycle. Salad rocket can be cut for the first time after about 20 days, and cutting continues until the plant bolts. In a plug-tray system with fertigation, in trials in Slovenia, salad rocket yielded 1.5 to 2.2 kg per square metre.

Two farm workers harvesting arugula by hand into plastic crates in the field

Rocket leaves are highly perishable, so the produce is cooled as quickly as possible after harvest.

Shelf life and post-harvest handling

Rocket leaves are highly perishable because of their high respiration rate, which limits shelf life. Harvest is best done in the cool hours, and the produce is cooled as quickly as possible. For ready-to-eat salads, leaves are washed, dried and packed under controlled conditions, so processors usually require clean produce, free of weeds and of holed or yellow leaves.

Frequently asked questions

What are the nitrate limits for rocket

Under Regulation (EU) No 1258/2011, 7,000 mg/kg for produce harvested from October to March and 6,000 mg/kg from April to September. These are almost double the limit for fresh spinach, but rocket, especially wild rocket, can exceed them with heavy nitrogen feeding.

How much nitrogen does arugula need

Less than is often applied. In a wild rocket trial, 66 to 82 kg of nitrogen per hectare gave the same yield as 309 kg, while higher rates raise leaf nitrate.

How many cuts can rocket give

In Italian trials, wild rocket gave four to five successive cuts in the same cycle. Salad rocket gives fewer, because it bolts sooner, especially with heat and long days.

Which rocket does the market prefer

For ready-to-eat salads, wild rocket is increasingly preferred, especially in Italy and Germany, where it covers a large share of the area. Salad rocket remains central for bunches and fast baby-leaf cycles.

What is the most damaging pest of arugula

Flea beetles, which make small holes in the leaves and render the produce unmarketable. The main protection is insect mesh on young plants.

Why does rocket spoil quickly after harvest

Because its leaves have a high respiration rate. Harvesting in the cool hours and rapid cooling are essential to keep quality.

Important notes

Densities, fertilisation and the number of cuts are adapted to the species, the growing system and the buyer's requirements, and treatment timing follows local plant protection guidance.

Use only products registered for rocket in your country, follow the label and the pre-harvest interval, and apply cultural measures first. For serious or persistent problems, consult a local agronomist for an accurate diagnosis.

For small plots and home use, growing arugula in the garden and in pots follows the same principles in simpler form.