Swiss chard is a leafy green vegetable, related to the common beet, prized for its colorful stalks and nutrient-dense leaves. This resilient plant is simple to grow, but successful, long-lasting harvests depend on planting during the cool seasons it prefers. Precise timing helps the plant avoid the stress of extreme summer heat, which can slow growth and reduce leaf quality.
Preparing Seeds Indoors
Starting seeds indoors offers gardeners a significant head start on the spring growing season. The optimal window for this is typically four to six weeks before the last expected spring frost date for your specific region. Sow seeds about a half-inch deep in a sterile seed-starting mix, placing two seeds per cell to ensure germination. While Swiss chard can germinate in soil temperatures as low as 50°F (10°C), an environment of 70°F to 85°F (21°C to 29°C) encourages the fastest sprouting.
After the seedlings emerge, place them immediately under strong light to prevent the stems from becoming weak and elongated, a condition known as legginess. Seedlings should be thinned to one plant per cell once they have developed their first set of true leaves. Before moving the young plants to the garden, they must undergo a hardening-off process, which involves gradually exposing them to sun and wind over a week or more.
Initial Outdoor Sowing Dates
Direct outdoor sowing is the most common method for planting Swiss chard, which thrives in cool soil. As a cold-tolerant crop, planting can begin two to four weeks before the average date of your last expected spring frost.
The most reliable indicator for initial planting is the soil temperature, not the air temperature. Swiss chard seeds will germinate in soil as cool as 40°F (5°C). For consistent sprouting, the soil should ideally reach at least 50°F (10°C).
When direct sowing, place seeds approximately six inches apart in rows spaced 12 to 18 inches apart. Since Swiss chard seeds often contain multiple embryos, thinning is necessary once seedlings are a few inches tall. Leave the strongest plant at each position to ensure proper spacing for mature, robust leaves and stalks.
Planting Strategy for Continuous Harvest
To maintain a steady supply of greens, gardeners should employ succession planting. This involves sowing small batches of seeds every two to three weeks following the initial spring planting. Continuing this staggered sowing until mid-summer prevents the entire crop from reaching maturity and bolting (going to seed). This strategy ensures a continuous yield of tender, flavorful leaves and stalks.
Swiss chard is highly tolerant of summer heat compared to other leafy greens, but its growth may slow in the hottest months. For a significant fall and winter harvest, a second major planting should occur in mid-to-late summer. Plant new seeds approximately six to eight weeks before the first expected fall frost.
Chard planted for a fall harvest often benefits from the season’s cooler temperatures. The flavor of the leaves tends to sweeten after they have been exposed to a light frost. These late-season plantings are exceptionally productive and can often be harvested well into the winter months in milder climates.