Arugula is a fast-growing, peppery cool-season green popular in salads and culinary dishes. Starting seeds indoors extends the harvest season, allowing you to enjoy this crop earlier than if you waited for suitable outdoor conditions. This method provides a jump start on the growing season, especially in regions with late spring frosts. By controlling the initial growing environment, gardeners ensure sturdy seedlings and achieve quicker maturity.
Determining the Optimal Indoor Starting Window
Arugula is a cool-weather crop that matures quickly, often ready for harvest in as little as 40 days after seeding. The primary factor for calculating the indoor start date is your local average last expected frost date. Start seedlings indoors approximately four to six weeks before this date to ensure they are the correct size for transplanting once the danger of hard frost has passed.
Starting seeds too early can result in leggy, overgrown seedlings that become stressed and prone to bolting once moved outside. Their fast growth rate makes a long stay inside unnecessary. Count backward four to six weeks from your final spring planting date to pinpoint the ideal indoor sowing day.
To ensure a continuous supply of fresh leaves, succession planting is highly effective. Sow a small batch of seeds indoors every two to three weeks until about a month before the weather heats up in late spring. This staggered planting schedule provides a steady yield until the summer heat causes the plants to become bitter and bolt.
Essential Conditions for Indoor Seedling Success
When starting arugula indoors, use shallow containers with adequate drainage holes. Fill them with a sterile, fine-textured seed-starting mix rather than standard potting soil. Sow the tiny seeds about one-quarter inch deep, barely covering them with the mix, and keep the soil consistently moist.
Arugula seeds germinate quickly, often within five to seven days, and thrive in cooler conditions than many other garden vegetables. The ideal temperature range for germination is between 40 and 55 degrees Fahrenheit, though growth after sprouting benefits from temperatures up to 65°F. Placing the seed trays in a cooler room helps mimic the plant’s preference for mild temperatures.
After germination, providing strong, consistent light is essential to prevent the seedlings from becoming “leggy,” or long and weak. A sunny windowsill is often insufficient, as the light is directional and rarely intense enough for the necessary 14 to 16 hours per day. Use a dedicated grow light positioned just a few inches above the emerging seedlings. As the plants grow, adjust the light upward to maintain a close distance, ensuring they receive the necessary light energy for stocky, robust growth.
Preparing Arugula Seedlings for the Garden
Before moving indoor-grown seedlings into the garden bed, they must undergo a gradual process called hardening off. This procedure toughens the plants by slowly acclimating them to harsher outdoor elements, such as direct sunlight, wind, and temperature fluctuations. The entire process should take approximately seven to ten days to prevent transplant shock, which can severely stunt growth.
Begin hardening off by placing the arugula seedlings in a sheltered, shady spot protected from wind for just one or two hours on the first day. Over the next few days, gradually increase the time they spend outside, ensuring they are brought back indoors each evening. As the week progresses, introduce them to progressively longer periods of direct sunlight, avoiding the intense midday sun initially.
Transplant the arugula when the soil is workable and the nighttime temperatures consistently remain above freezing. Arugula is relatively cold-tolerant and can handle a light frost once established, but the hardening process ensures they can withstand the fluctuations of early spring weather.