Unlike many vegetables which require warmer temperatures to germinate, most greens are “cold hardy”, meaning that you can plant them long before the last frost. But just planting your greens doesn’t ensure a healthy crop. Here are a few tips to help you achieve success when cultivating early spring greens in your garden.
1. Ensure your soil is ready
The seeds of most greens will germinate at temperatures as low as 40 degrees F, which means you can begin planting as soon as the soil has thawed and is dry enough to rake smoothly. Overly wet soils may rot your seed, so if you live in an area with a high water table or copious rainfall, be sure you aren’t rushing the season. A good way to test your soil for readiness is to squeeze a fist full in your hand. If the soil forms a ball that separates easily or crumbles through your fingers, it’s dry enough to begin planting. If the soil forms a ball that doesn’t separate when jiggled, wait a few more days and try again.
If your soil is too wet, consider installing raised beds to improve early-season growing conditions. Raising your beds 12-24” above the ground is often all you need to improve soil conditions and ensure adequate drainage. You can also install sub-drainage or ditches if your space is large enough to warrant the cost.
Lastly, if your soil is too wet because of a high clay content, consider improving soil quality by adding some sand and organic matter such as compost and rotted manure. The ideal soil type for growing vegetables is sandy-loam.
2. Provide adequate nutrients for healthy growth
Like all plants, lettuces and other salad greens require nitrogen, phosphorous and potassium to grow. However, in salad greens the bulk of the plant’s energy is used up making green leaves. For this reason, these plants rely most heavily on nitrogen for healthy production. Fertilizing your soil with finished compost or rotted animal manure before planting is one way to deliver nitrogen to your plants’ roots. We also top dress with compost after the seeds have emerged (if planting in rows) or water with diluted fish fertilizer or compost tea. Other sources of nitrogen include organic alfalfa or kelp meal worked into the soil before planting.
3. Keep soil evenly moist
One of the mistakes many gardeners make when growing early greens is overwatering. Although the soil is warming up along with the air, those cold spring temperatures mean less evaporation. While some experts advocate misting your greens, particularly before germination, we’ve found a light watering twice per week is enough to quench our plants’ thirst and ensure strong, healthy development. Frequency will depend on your soil (whether it is sand, clay, or loam), the temperatures in your region, and whether your crop is outside or in a greenhouse.
4. Provide primary and secondary cover
To get a head start on the season, you can plant greens in a greenhouse or hoop tunnel a full month before their outdoor planting dates. You can also go one step further: although seeds grown in a greenhouse already benefit from warmer-than-average temperatures, an extra layer of protection can speed growth and improve germination. In The Winter Harvest Handbook, Eliot Coleman describes how floating row covers (a thin layer of light-permeable cloth) can substantially increase the temperature and relative humidity of a growing area inside a greenhouse. This “double coverage” modifies the climate enough to spur on growth and protect plants from unexpected dips in temperature. Lightweight, floating row covers are now widely available at most garden suppliers. After starting a selection of early greens in our greenhouse, we cover our seeds for the first few weeks after planting to speed germination and maintain an even soil moisture early in the season.
5. Choose cold-hardy varieties
Although most greens are tolerant of the cold, some are more likely to germinate and thrive in unpredictable, swinging temperatures than others. Arugula, spinach, kale, cress, mustard greens, and corn salad are all good choices for an early spring sowing. In most locations, lettuces will germinate in a greenhouse in early spring. Though they may grow more slowly than other greens at the beginning of the season and they require protection from hard frosts, lettuces add bulk and sweetness to the mix. Keep in mind that most lettuces require light to germinate, so a thin covering of soil is all they need to get started. See our list below of favorite cold-hardy greens below for more details.
Favorite Cold-Hardy Greens
The following greens will germinate and thrive in cool temperatures. We start a variety in our greenhouse in early spring to use in salad mixes, making sure to select for texture, colour, and nutrients. We also sow directly into the garden in consecutive plantings spaced 2-3 weeks apart to ensure a continuous harvest.
(Also known as “rocket”) is an easy-to-grow early spring green that will germinate in the coldest spring soil, earlier in a greenhouse. Sow in rows or broadcast the seed evenly, but thin to 4-6” (10-15 cm) apart after emergence or the plants will bolt prematurely. When the plants do produce flowers, you can prolong production by pinching them off.
Are great for color. The bright red-and-green combination adds brilliance to salads and tastes delicious when harvested at the baby-green stage (less than 4” or 10cm). Like other early greens, beets can be sown in a greenhouse as soon as the soil can be worked. Cool temperatures will intensify the colour in some varieties.
Or “Miner’s Lettuce”, has long been considered a weed in North America, but its succulent texture and tolerance for cold temperatures has made inroads with gardeners and upscale restaurants over the last few decades. Its small, white flowers are equally edible and add interest to salad mixes.
(Also known as mȃche) is a favorite cool-weather crop with a mild, nutty flavour. Harvest the outer leaves or cut the entire inner rosette and watch it regrow. Although corn salad takes as long as lettuce to mature (about 50 days), it germinates faster and earlier, making it a great addition to early salads.
(Or shungiku) is an early green with Asian origins. Harvest the leaves or the edible flowers for a mildly bitter addition to salads and stir fries.
Is a year-round staple at our house, but one of our favorite ways to eat this calcium-rich plant is as a baby green in a mixed salad. If planted in spring, kale will germinate at soil temperatures at 40° F or higher. In a greenhouse, kale will produce quickly and flesh out salads with its vast array of colours and textures. We prefer Red Russian for our salad mix—its purple veins and frilly edges add a touch of fancy to any meal. Harvest the outer leaves of each plant when they are no more than 4” (10cm) long and sow more thickly than you would for mature plants.
Is a staple in any salad, but the vast array of varieties available today mean choices in colour, texture, and flavour. One thing to keep in mind if growing lettuce in a greenhouse is that some varieties will hold better than others into the heat of summer, ensuring a longer harvest and a steady supply. If you would like to keep your plants going after the weather warms up (or while waiting for those outdoor plantings to begin producing), choose a bolt-resistant variety (one that will not go to seed quickly). Oak leaf lettuces such as Salad Bowl have performed incredibly well in our greenhouses over the years. Other favorites include Red Sails and Lovelock.
Mustard greens, such as Mizuna, Giant Red, and Tah Tsai add spice to salads and can also be cooked in stir fries or soups. All belong to the Brassica family (the same family as broccoli, cabbages, and arugula), which means they share some of the same pests. Unlike broccoli and cabbages, however, mustards grow quickly and then go to seed. Although you can plant them outside your greenhouse in the coolest of temperatures, greenhouse growing ensures an earlier, more even harvest.
Pea greens include the top 3-4” (7.5-10 cm) of any edible pea plant. I first encountered pea greens while working on an organic greens farm where workers harvested the leafy, vining tops rather than waiting for the pods to develop. Pea greens are only tender enough if you harvest them when plants are young. Cut the entire plant top once or twice before trellising and allowing to mature for your pea crop.
Sorrel stands out as a must-have in our garden. As one of the few perennial greens available today, sorrel produces first in the spring when most other greens are just going into the ground as seeds. Sorrel’s large and delicious leaves have a distinct, lemon flavor. They make a great edition to any salad or sandwich.
Spinach is another early staple that fleshes out salad mixes and adds vital nutrients to meals. We harvest our greenhouse spinach at the baby-green stage, taking the outer leaves and allowing plants to regrow. Spinach does best in fertile soil that is well-drained and warmer than 35° F. Sow early, but remember that spinach will go to seed in a greenhouse as soon as the weather warms up. Although you can sow outside almost as soon as the soil can be worked, we’ve found a greenhouse crop of spinach out-produces its outdoor cousins by up to 4 weeks, making both plantings worthwhile.
Favorite Spring Mixes:
If space is limited, consider growing a selection of greens to suit your palate. Here are some of our favorite blends organized by taste:
Looseleaf lettuce (e.g. Salad Bowl or Red Salad Bowl), Butterhead lettuce (Buttercrunch), Romaine lettuce (Freckles or Conquistador), spinach, claytonia, beet greens, pea shoots.
Looseleaf lettuce (choose one red and one green variety), Romaine lettuce, arugula, tah tsai, mizuna, edible chrysanthemum (shungiku).
Looseleaf lettuce, Romaine lettuce, arugula, claytonia, kale, corn salad, beet greens, sorrel.
A Final Word
Growing spring greens for salad mixes is a satisfying way to get started in the garden before long days and warmer soil temperatures arrive in full force. It’s also one way to save money and improve the quality of your salads with just a little bit of effort.