Arugula is a popular, fast-growing annual green known for its distinct peppery flavor. Successful cultivation starts with the correct planting technique, particularly determining the appropriate number of seeds for each location. Getting the seeding rate right is important because it directly affects the health of the mature plants and the efficiency of the garden space.
Site Preparation for Arugula
Arugula thrives best in cooler weather, typically planted in early spring or late summer and fall. The ideal soil should be well-draining, loose, and rich in organic matter, achieved by incorporating compost before planting. Arugula prefers a soil pH that is slightly acidic to neutral, generally between 6.0 and 7.0.
The plant grows well in full sun (at least six hours of direct light) but tolerates partial shade, especially in warmer climates. Afternoon shade helps prevent premature bolting, or going to seed, which is triggered by high heat. Arugula seeds can germinate in soil temperatures as low as 40°F (4°C), allowing them to be sown outdoors as soon as the ground is workable.
Recommended Seeding Rate and Rationale
For consistent results, the recommended practice is to sow two to three seeds at each intended planting spot. This method acts as germination insurance, acknowledging that not every seed will sprout successfully. Planting multiple small seeds significantly increases the probability of having at least one viable seedling emerge.
Using this higher seeding rate accounts for potential variations in seed viability or less-than-perfect soil conditions. If only one seed were planted, a single failure would result in a noticeable gap in the garden row. Using two or three seeds ensures a full stand of plants, though it requires a follow-up action known as thinning.
Planting Depth and Row Spacing
Because arugula seeds are small, they must be planted very shallowly to ensure they have enough energy to reach the soil surface. The optimal planting depth is about one-quarter inch deep. Planting any deeper may prevent seedlings from emerging and can reduce the germination rate.
Once the seeding rate is determined, consider the spacing between planting spots. For rows, seeds should initially be spaced about one inch apart, with rows separated by 10 to 12 inches for adequate air circulation. If growing arugula to a mature size, a final spacing of six inches between plants is required after thinning.
Management After Germination
Arugula seeds typically germinate quickly, often within seven days of planting, especially when the soil is kept consistently moist. Once seedlings emerge, management focuses on preventing overcrowding. Competition for sunlight, water, and nutrients will weaken the plants if they are left too close together.
Thinning should occur once the seedlings develop their first set of “true leaves” (the second pair of leaves that emerge after the initial cotyledons). To thin, select the strongest seedling at each spot and gently snip the others at the soil line using small scissors. Pulling unwanted seedlings out is not recommended, as this can disturb the shallow roots of the remaining plant. The thinned seedlings are edible and can be used immediately as microgreens. Consistent watering is important throughout the growing period, as dry soil can cause the plant to bolt prematurely, leading to a bitter flavor.