By Sheri Hunter, Master Gardener, Colorado State University Cooperative Extension, Denver County

Lettuce has been grown and used by the Greeks and Persians since 500 B.C.

Today, a huge number of varieties of Lactuca sativa have been bred from early wild forms. Suitable for gardens large and small, ornamental or edible, these varieties are grown from the far north to the south of the North American continent.

The Seed Savers Exchange Garden Seed Inventory (fourth edition) lists 381 varieties of lettuce. Choice abounds. Do you want to grow leaf varieties, romaines or heads with foliage frilly and notched or broad and wavy? Available colors include deep green, white, yellow, bronze, deep red, or burgundy. Some produce perfect compact heads, while others form bright, informal leafy hedges. All add a sort of elegance rare in a vegetable garden.

Lettuces are not only esthetically appealing, nutritionally they are good sources of calcium. Green leafy varieties also supply vitamins A, C, B1 and B2.

Unfortunately, many lettuces are difficult to ship and preserve for marketing purposes. Commercial growers annually supply only a few varieties. In some months of the year lettuce becomes expensive, scarce or altogether unavailable.

There are many reasons to grow lettuce. Considering its popularity in salads, it is a wonder that lettuce isn't more prevalent than ornamental cabbage in Denver gardens.

The answer may lie in the problem of cultivating lettuce in our high desert plain. Lettuces require fertile soil, high in organic matter. Some lettuces prefer cooler, more humid conditions and become tough, scorched or bitter in harsh sunlight and heat.

For the vegetable gardener determined to enjoy the rewards of growing lettuce, here are the keys to success. In Colorado, soil amendment and water conservation are essential. Beyond that, it is simply important to plant the right lettuce, in the right place, at the right time of year.

Soil Amendment and Drip Irrigation

A fertile soil that retains moisture yet drains well, is ideal for growing lettuce. Most Colorado soils will require ample organic matter such as composted, coarse, fibrous material to shoulder apart soil particles. This enables moisture to drain and oxygen to filter into the root zone. Added nitrogen in some form--well-composted manure, or cottonseed meal--is important for the rapid leafy growth that produces the best lettuces.

Even soil moisture and constant surface humidity promote tender lettuce leaves. While overhead watering and surface irrigation enable slugs to travel and fungus to grow, a special technique provides for tender growth while conserving water resources in our arid environment.

Install a soaker hose an inch or more beneath the soil surface in a slightly mounded row before planting seed. This technique keeps the soil surface dry reducing the chances of predation and disease caused by birds, slugs, fungi, and other pests associated with moist conditions.

After seeding, cover the area with a floating row cover tunnel. Leave this tunnel in place throughout the growing season, removing it only to thin or harvest. Thin lettuce progressively. That is, keep the lettuce growth dense rather than widely spaced. Thin plants only as they develop and leaves begin to crowd. Lettuce thickly grown under a row cover holds in humidity for tender leaves even in warm conditions


Lettuce throughout the Year

Lettuce is generally sown directly into the soil, 1/4 to 1/2 inch deep.

Temperature is extremely important when growing lettuce. Generally, lettuces prefer cool temperatures. Lettuce seed sprouts best at 60-65 degrees Fahrenheit. At 80 degrees and above, lettuce seed will sometimes not germinate at all.

Once plants are up and growing, different temperature responses are also seen. Some types bred for northern areas tolerate very cool temperatures--even light frost--but wilt upon sustained exposure to cold. On the opposite end of the temperature spectrum, certain varieties do well in warmth while others bolt or become bitter. Consequently, it is important to select the right lettuce for the right time of year.

Lettuce planted in full sun, especially in south or southwest facing gardens, may experience a sudden rise in leaf temperature, producing a scorched appearance. Moderating this temperature change with floating row cover reduces leaf scorch. Lettuce can be successfully grown in partial shade during hot summer months. Winter lettuces grown in cold frames with southern exposure do produce well. However, gardeners may need to ventilate the frame during the midday hours of warmer days.

With an extra bit of effort at planting time, bountiful lettuce yields are possible on a year-round basis. The esthetic and nutritional, if not the economic reasons for growing lettuce make it a smart and rewarding choice for any Denver garden. The tables below offers a few suggestions of varieties for growing lettuce year round.

Spring/Fall Lettuces

Summer Lettuces

Winter Lettuces

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