Leafy Greens - Planting and Spacing
Most of the leafy green vegetables will germinate at soil temperatures of 32-35°F, with an optimum germination range of 55-70°F. Soil temperatures above 80°F cause the seeds of some crops (lettuce, spinach, others) to go dormant and they will not germinate until cooler soil temperatures return. When conditions are cooler, water after seeding and plant later in the day to overcome dormancy effects. Once the crops are established (emerged), high temperatures (80+°F) cause many to bolt and form a seed head. Since many of these vegetables mature quickly (40 to 60 days), and days to harvest is impacted by temperature, it is crucial to use sequential plantings to get consistent production. Seeds are commonly planted ¼ - ⅓ inches deep and thus are regularly subjected to warmer soil conditions.
Most of the leafy green crops have similar spacing and seeding requirements (Seed Quantities Table). Growers should purchase the best quality seed available to help ensure uniformity of germination which then leads to more even plant growth. Use modern precision planters when seeding and purchase seeds that are coated to allow singulation of seed placement. Fungicides should be used (in coatings or applied to raw seed) particularly if establishment issues have been encountered (see Diseases). Always plant in well-prepared seedbeds to ensure uniform planting depths. Seeds that are primed can help speed up seedling establishment particularly in harsh (cold or hot) growing environments. Doing all of these helps ensure rapid and uniform establishment. It is fairly common to irrigate after seeding to promote more uniform emergence.
Final spacing on heading crops (lettuce, endive, and escarole) varies depending on plant size at harvest. Other types (leaf lettuce, spinach, baby greens, kale, and arugula) are planted at tighter row widths. Regardless of the crop, spacing should allow good air movement around the plants to minimize common diseases like grey mold (Botrytis), bottom rot (Rhizoctonia), and leaf drop (Sclerotinia). Planting on raised beds (3-4 feet wide; 4 inches high; 3-4 rows per bed) helps with air movement and encourages drier soil conditions. As with all crops, rotate planting sites wherever possible.
Transplants are often used for early lettuce production but can be used on most of the leafy green vegetables. Transplants can be used in all production seasons and are particularly suited for very early spring (February-April) or late fall (September-November) plantings in tunnels or the field. Transplants should be planted when they are 3 to 4 weeks old (grown in 128 or 256 cell trays). Use floating row covers or low tunnels over the beds in combination with early transplanting. Don’t over harden transplants, use a starter fertilizer to reduce transplant shock, and irrigate immediately after planting. Summer transplanting works well when slow-bolting, heat tolerant varieties are selected. In hot summer conditions, remember to germinate seeds in a cool location before growing out plants in the greenhouse or shade house (pay careful attention to air temperatures).
Leafy green mixes are commonly seeded at very high densities with seeding rates depending on seed size and crop species. Spacing between plants is often less than 1 inch; with rows about 2 to 3 inches apart on 30-36 inches wide beds. Seeds can be broadcast on the soil surface and raked in, or spread on rows with a hand-operated precision seeder. Because seedling emergence may vary from 3 to 15 days at the optimum germination temperatures (55 - 70°F), each crop of a mix is typically grown separately. Multiple varieties or crops may be grown together, however, different germination times and rates of growth makes harvest coordination difficult. Leafy green mixes are very short season crops (25-40 days). The time from planting to harvest is longer for fall to winter (September – February) plantings than for early spring to summer (March – June).
For all leafy green crops, winter production in Utah is possible. Low light and cold temperatures in winter (particularly December-January) make production times quite long, so cold-hardy species and transplants should be used. Always use low tunnels or row covers in winter since repeated exposure to freezing temperatures will reduce the quality of even the hardiest plants. The best way to determine timing is to experiment in your own system. For a starting point, see the lettuce or spinach high tunnel publications (USU) or consult the Winter Growing Guide (Johnny’s Seed).
Seed quantities, field seeding rates, and common row spacing for leafy green vegetables
|Leafy Green Vegetable||Seeds (per unit weight)||Field Seeding (lbs/acre)1||Row Spacing (inches)|
|*seeding rates depend on plant type; some are commonly transplanted
1Lower quantities of seed will be needed if transplanting