Salad Mix and Microgreens

Introduction

Salad mix, mesclun mix, and spring mix are interchangeable terms used to describe assorted mixed greens harvested at the seedling, or "baby leaf," stage (3–5 weeks after seeding). Blends usually include 5–7 types of greens with a range of leaf sizes, colors, shapes, and textures. Most mixes include leaf lettuces and other greens (most commonly Brassica species) to add diversity in flavor, texture, and color. Pre-mixed seed blends can be purchased, or a custom mix can be made by combining individual varieties. Mixes can be mild or spicy, and can be harvested young for use in salads or older as "braising" mixes.

Microgreens, like salad mix, can be grown and sold as either individual species or a mix. They are most commonly used as garnishes, where small quantities add touches of unique flavors. Therefore, in addition to species typically grown for salad mix, popular microgreens also include certain herbs and vegetables. Microgreens are harvested at 1 or 2 true leaves (depending on the species) and therefore can be produced quickly, usually in trays in a greenhouse. 

Types and Varieties

In general, Brassica species contribute spicy or pungent flavors, while the lettuces and amaranths are mild and sweet. Varieties are selected not only for flavor and leaf texture, but also for color. Red varieties that are well-suited for salad mix production are those that develop good red color even under low light conditions. For cool-weather or winter production, cold-hardy species such as spinach, claytonia (miner's lettuce), kale, and other brassicas are recommended. Choosing lettuce and spinach cultivars with resistance to a wide array of races of downy mildew is especially important for cool season production.

Types and Varieties of Crops used in Salad Mix

In addition to the crops and cultivars listed above, microgreens may include the following:

Soil Fertility

Salad mix crops grow rapidly and require relatively little fertilizer. Sidedressing is usually not needed. If planted following another crop, additional fertilizer for salad mix may not be necessary. Microgreens require very little to no fertility; they can be grown directly in trays of quality potting mix with no supplemental fertility.

Plant Nutrient Recommendations According to Soil Test Results for Salad Mix

Planting

Salad mixes are typically seeded at high densities to ensure good yields and to shade out weeds. Seeding rates vary with seed size and species, but common spacing is less than 1" between plants with 2"–3" between rows on 30" wide beds. Seed can be broadcast, but is often seeded 1–6 rows at a time using a hand- or tractor-driven precision seeder. For larger-scale production, 17-row mechanical seeders are often used. Germination may take anywhere from 2–15 days at the optimum germination temperature (55ºF–70ºF). Follow specific germination requirements for each component of the mix. Generally, salad mix components are cool-season crops that will germinate poorly when night temperatures exceed 80ºF. Germination of some species can be inhibited by heat and light; shading may be necessary for adequate germination and growth in mid-summer.

When creating a custom mix, each component is often grown separately and mixed after harvesting since growth rates vary greatly with species, day length, total light, and temperature. In general, lettuces take 10–14 days longer from seed to harvest than most brassicas. Note, though, that mixing species postharvest, rather than mixing seed and harvesting as a salad mix, may lead to the finished product being interpreted as a processed rather than raw agricultural product for food safety purposes, according to some regulatory agencies. Be aware of how local regulators view these products.

The time from planting to harvest will be 2–3 times longer for fall (September to February) plantings than for late spring or early summer plantings. Consistent harvest throughout the growing season requires carefully planned succession plantings. Winter production in New England is possible, but low light and cool temperatures make production time longer than in summer, and cold-hardy species should be used. Prolonged exposure to temperatures below freezing (32ºF) will reduce the quality of even the hardiest species. The best way to determine timing is to experiment in your own system. See the Johnny’s Selected Seeds Winter Growing Guide for starting point recommendations.

Microgreens are grown in potting media in row trays or shallow, flat trays. Since microgreens are harvested so young, their root systems do not need full-depth trays, and both row trays and shallow, flat trays help conserve media. Optimal seeding densities and growing conditions vary by species. Heating mats are beneficial for winter greenhouse conditions.

Harvest and Storage

Salad mix greens can be harvested 3–5 weeks after seeding, depending on the species and growing conditions. Flavors intensify and leaf textures change with age, so optimum harvest time will depend on yields required and the intended use of the final mix. Harvesting can be done by hand-cutting approximately 1" above the soil line using scissors or knives. Mechanical or hand-driven saw-like harvesters are used for large-scale production. Some varieties will re-grow to permit multiple harvests, but the second harvest will be less uniform and may be of lower quality. After harvest, salad mix components should be washed, dried, and cooled prior to packaging in bags or plastic-lined boxes. Young leaves are tender and susceptible to bruising, and therefore must be handled very gently after harvest. Rapid cooling by washing with near-freezing water will greatly prolong shelf life. Greens are then dried using salad spinners or custom-made commercial spinners with larger capacity. 

Microgreens can be harvested 2–3 weeks after sowing, after the development of 1–2 true leaves, which confer visual interest, texture, and loft to the final product. Some species, including fennel, only develop their characteristic flavor when they have 2 true leaves. Like salad mix greens, time to harvest depends on species and growing conditions. Microgreens are cut with scissors as close to the soil as possible, and may be washed and dried in salad spinners. Microgreens are highly perishable and do not typically keep beyond 5 days.

Salad mix and microgreens should be stored as close to 32ºF as possible with 98%–100% relative humidity. Food safety issues from microbial contamination are often linked to leafy greens that are eaten raw. It is important to follow some basic practices that are in accord with the guidance outlined in the Food Safety section of this guide.