Cold Frame Addon: Spinach, arugula extend season

Using a cold frame addon over a raised bed is an ideal way to harvest spinach and arugula long after the main garden season has ended. Both crops are exceptionally cold-hardy, and the microclimate created by the frame provides just enough protection to keep them productive through freezes and light snow. This method allows for a late fall and early winter harvest, as well as a jump-start on the spring season.

For a fall and winter harvest, sow spinach and arugula seeds directly into the raised bed in late summer or early fall, typically 6-8 weeks before your average first frost date. This gives the plants enough time to establish a solid root system and produce several sets of true leaves before severe cold arrives. Plant the seeds slightly deeper and denser than you would for a summer crop. Once the seedlings are established, or just before the first hard frost is predicted, install the cold frame lid over the bed.

The single most critical task for managing a cold frame for spinach and arugula is ventilation. On any sunny day, regardless of the outside air temperature, the inside of the frame can heat up dramatically, cooking your plants. You must prop the lid open in the morning to allow heat to escape and air to circulate. A simple block of wood works well. Close the lid in the late afternoon to trap residual warmth for the night. Aim to keep the internal temperature from exceeding 60°F. An automatic vent opener, which operates on a wax-filled piston that expands with heat, can automate this daily chore.

Watering needs are minimal during the cold months. The soil inside the frame will stay moist much longer than in an open garden. Check the soil moisture weekly by touch; only water when the top inch feels dry. When you do water, do so in the morning on a milder day to ensure the foliage has time to dry before temperatures drop at night, which helps prevent rot and fungal diseases.

Harvesting is best done using the cut-and-come-again method. Snip the larger, outer leaves from each plant with scissors, leaving the smaller inner leaves and the central growing crown intact. This encourages the plant to continue producing new leaves. You can harvest every week or two throughout the late fall and into the winter. Growth will slow significantly during the shortest, coldest days of December and January but will pick back up as the days lengthen in February.

For an extra-early spring crop, you can sow seeds directly into the soil inside the cold frame in late winter, often as early as February in many climates. The protected environment will allow the seeds to germinate and grow weeks before you could plant anything in the open garden. By the time your last frost date arrives, you will already be harvesting fresh greens. Once the weather warms consistently in spring and daytime temperatures are regularly above 50°F, you can remove the lid entirely to prevent the plants from bolting prematurely.