If you only had space to grow a single food crop, you would be hard pressed to find a better choice than lettuce and other salad greens. The selection that is available and the fresh picked taste cannot be matched by anything that is available at the grocers. Greens don’t travel and store well, and gourmet greens are expensive. The good news is that lettuce is relatively easy to grow, lovely to look at and has a short time to harvest.
With over 800 recognized varieties in the United States alone, selecting varieties to grow can be quite daunting. For simplicity, lettuce varieties fall into three types of head lettuce and what are referred to as loose leaf varieties. Those with large gardens may have fun experimenting with various types of head lettuce, but for the average home gardener wanting a supply of fresh, nutritious salad greens, there are some advantages to starting with the loose-leaf varieties. One of the distinct advantages of loose-leaf varieties is that most of them are cut-and-come-again plants and can be harvested one leaf at a time so you can pick just enough for tonight’s salad and leave the plant to produce more. The loose-leaf varieties tend to be more heat tolerant, bolt resistant and quicker to mature. Before presenting some great sources for selecting seeds, it is important to arm yourself with some need-to-know terminology.
There is a growing trend in vegetable gardening to return to open pollinated (rather than hybrid) varieties, and salad greens are no exception. True heirloom varieties were produced at least 50 years ago and have some unique history associated with them. Perhaps the primary reason for the popularity of heirloom varieties is the belief among fans that they have superior taste.
All American Selections
This rating is a great way to help narrow the selection of seeds for growing great salad greens. The nonprofit organization does extensive testing on factors such as taste, earliness and ease of harvesting and resistance to disease and pests. Choosing AAS varieties is a great way to select the best varieties. Seed companies designate their AAS offerings and more can be found out about AAS at All-AmericaSelections.org.
Slow-Bolting and Heat Tolerant
Plant developers have had some success with developing varieties of lettuce that are more heat tolerant and slower to bolt but make no mistake about it lettuce is still primarily a cool weather crop. Still, for warmer climates or if you are trying to extend the spring season, it is worth considering these designations when selecting seeds.
Days to Maturity
One of the nice things about growing loose leaf varieties is that the leaves can be harvested any time they are large enough to eat. Baby greens are prized for their tenderness and mild taste. Leaves left on the plant too long tend to be tougher and may be bitter. Still, it is a good idea to consider the days to maturity listed for each variety. Some varieties may mature in as little as 30 days with others taking up to 90. In addition to staggering planting, selecting varieties with differing days to maturity is an effective means of extending the harvest season.
A great strategy for home gardeners is to plant some of the wonderful seed mixes that are available, rather than selecting single varieties, or trying to mix your own seeds at first. The gourmet salad greens that are increasing in popularity in the best restaurants and some grocery stores marketed under names like “mesclun”, “baby greens”, “designer greens” etc. are actually mixtures of several lettuce verities that have been carefully pared to complement one another both in the garden and on the plate.
Lettuce is a cool season crop and consequently is best grown in either spring or fall. It grows best when temperatures are between 60-70F, but many varieties can handle daytime temperatures up to the mid 80s with proper shade and watering. Pay close attention to the planting directions on the seed packet. Some lettuce seeds need light to germinate. Just barely cover the seed with soil or you can merely press the seeds into good contact with finely prepared soil without covering them. Care must be taken to keep the seedbed moist, but not soggy, until the seedlings emerge.
Lettuce can be direct seeded in the garden or containers, but a better option is to start seeds in proper seeding medium inside, or in a greenhouse. This allows one to start spring seeding a few weeks early while it is still too cold outside and fall seeding a few weeks early while it is still too hot outside. In any event, staggering starts every couple weeks will help keep supply constant and extend the harvest. By moving to more shady areas as the season heats up you may be surprised how long you can keep the lettuce coming.
It generally takes only a couple of weeks for roots to branch out to the sides of the seeding plugs and they are hardy enough to go in the ground after proper hardening off. This can be accomplished in a few days by gradually exposing the seedlings to the outdoor environment starting with two hours on day one and then doubling the time each day for four to five days. Start with a full shaded patio location and gradually move the seedlings into more open conditions.
Loose leaf varieties can be spaced at six-inch intervals, regardless of what it may say on the seed packet, but head lettuce varieties often require more space.
Care and Feeding
Soil pH should be in the 6-7 range for best results. A wide range of well-drained soils can be used successfully to cultivate lettuce. Extra nitrogen can’t hurt, so soils high in well rotted manure or compost are desirable. The soil should be high in organic content and have good water holding capacity. Because of the shallow root system, deep cultivation is not necessary, but care should be taken to provide 3-6 inches of good quality soil. Sprinkling wood ash from the fireplace around lettuce plants helps aid vigorous growth and discourages slugs.
Watering and Feeding
Due to its shallow root system, lettuce needs regular watering, but sitting in soggy soil will increase the chance of harmful fungus problems and slugs. Drip irrigation is an effective watering tool for lettuce because it can deliver frequent light watering. Weeding is also imperative because lettuce, with its shallow root system cannot compete with weeds for water. Heavy nitrogen feeding, particularly as things heat up, helps to keep plants growing vigorously. Planting often, feeding well, and harvesting early is the name of the game with lettuce.
Keep Things Cool
The hotter it gets, the more likely lettuce is to bolt. Bolting is a term that refers to a sudden spurt of growth which results in long stems with few leaves almost overnight. Once lettuce bolts, the leaves will be bitter, and the plant will no longer be productive. The best defense against bolting is to grow lettuce in the cooler shoulder seasons, but there are a few things that can be done to help create a cooler micro climate when things get hot. Mulch helps to keep the ground cool and to keep weeds down, but if saturated, it can also attract fungus and slug problems. Using drip irrigation helps to keep soil moist without saturating mulch. Providing more shade as the weather gets hotter is also essential and lettuce does well in the shade.
Companion planting is a great strategy to use with lettuce. Because lettuce has a shallow root system, it can be grown close to taller plants like sweet corn without interfering with their deep roots. The taller plants will shade the lettuce, and the lettuce will provide ground cover; which, along with mulch, will help to keep the soil cool. Common companions for lettuce are carrots, cucumbers, radish, and strawberries. Onions and green onions interspersed with lettuce may even help to repel rabbits and some other pests. All the mints including hyssop, sage, and various balms, help to repel slugs, but can be a problem because of their invasive nature. To get around this, plant mint in small containers and sink these in the ground between lettuce plants. Read this article for more information on companion planting.
Harvesting and Enjoying
Harvesting lettuce at the correct time is important for maximizing its flavor and texture. If you let your lettuce crop sit in the garden too long, it will increase in bitterness and the leaves will become tougher. Early morning is the best time to harvest the lettuce needed for a night’s meal. This also allows for the lettuce to be washed, dried and chilled and helps avoid wilting. A few hours in the refrigerator can even help soften the bitterness of older leaves.
Use sharp scissors or a sharp knife to harvest when greens are 3 to 5 inches tall. Cut at least one inch above the soil level, always leaving the growing tip intact. Gently wash and dry the leaves. For this task, an inexpensive salad spinner is a great investment. Store the washed/dried cut greens in an airtight plastic bag in the refrigerator and use them as soon as possible. Do not store lettuce with apples, pears, or bananas. These fruits release ethylene gas, a natural ripening agent, which will cause the lettuce to develop brown spots and decay quickly. Always serve lettuce dry and add dressing at the last minute. Salad dressing will cling to dry lettuce leaves instead of sliding off to the bottom of the salad bowl. Toss with dressing just before serving or serve dressing on the side. Lettuce leaves covered with dressing will quickly wilt.
If manure or compost is used in your garden, it is best followed with an organic mulch to help keep harmful bacteria from splashing on the leaves. As an added precaution, greens grown in soil that has compost or manure can be washed with a 10% hydrogen peroxide solution to avoid the possibility of food poisoning. Be sure to rinse and dry greens well after washing.
Iceberg lettuce is the most popular lettuce in the United States. If you are growing leaf lettuce, you will be glad to know that the dark green leaves of most loose-leaf varieties always indicate higher fiber, flavor and nutritional value. Green lettuce is a good source of vitamin A from beta carotene and potassium and a moderately good source of vitamin C.
Dr. Christopher J. Kline is a master gardener and writer living in Paradise Valley Arizona.