Lettuce (Lactuva sativa) is an annual plant that belongs to the family Asteraceae. It is native to Southern Europe and Western Asia. This plant descended from wild lettuce latica scariola, a common weed of roadsides and wastelands in both ancient and modern times.
Lettuce is a very nutritious food source and generally the darker the leaf the more nutritional value it has. It is a very good source of vitamins A, K, C, folate, manganese and chromium.
Probably the leafiest and greenest of the leafy greens, lettuce is ‘The King’ when it comes to getting antioxidants and vitamins. A reason why it is gradually gaining much popularity in Nigeria and Africa.
Lettuce is easily cultivated, and it requires low temperatures to prevent the plant from flowering quickly.
Growing lettuce could be a very profitable agribusiness for agripreneurs when properly done. It is therefore imperative to note the following guidelines while embarking on lettuce farming.

KNOWING YOUR VARIETIES
There are four distinct types of lettuce – leaf (also known as looseleaf), Cos or romaine, crisphead, and butterhead.
SOIL REQUIREMENTS
The plant grows well on a wide variety of soils ranging from light sand to heavy clay, however, best results are obtained on fertile loams that are rich in organic matter.
A pH between 5,5 and 7 is optimum. Lettuce should be grown on soils with a high water-holding capacity and proper drainage for good root growth and plant performance.
Soil test your farm and lime the soil to raise the pH above.
PLANTING REQUIREMENTS
Before you plant your lettuce seeds, make sure the soil is prepared. It should be loose and drained well so it’s moist without staying soggy.
To keep the soil fertile, feed it with organic matter about one week before you seed or transplant. Since the seed is so small, a well-tilled seedbed is essential.
Lettuce is regularly sown directly in the field to a depth of 10 to 15 mm. The seedlings are later thinned out to the desired spacing and they are sometimes used for transplanting.
TRANSPLANTING SEEDLINGS
Seedlings should be transplanted between 4 – 6 weeks after sowing. Seedlings must be transplanted at the correct depth in a little planting hole that has been made in the ground prior to planting.
If the seedlings are forced into the ground, without a hole being prepared for them to be inserted into, the root system will be damaged and the plant will experience stress resulting in poor yield.
Once the seedling is placed inside the hole the area should be firmed so that sufficient contact is made between the seedling and the soil.
CLIMATIC REQUIREMENTS
Temperature
Lettuce is a cool season crop that grows best within a temperature range of 12 °C to 20 °C. It does not suffer from light frosts and winter cold except near maturity.
Severe frost before harvest can scorch leaves and heads. Temperatures above 27 °C affect head development and plant edible quality and also promote premature seed stalk development. High temperatures also inhibit germination and can cause a high incidence of tip burn.
Rainfall
The crop has high moisture requirements and not more than 50% of the available water in the root zone should be depleted before irrigation.
FERTILIZER APPLICATION
Apply phosphorus and potassium fertilizers prior to planting. Nitrogen fertilization should be kept to a minimum prior to planting.
Apply nitrogen as a side-dress application once the crop is established. Frequent, light watering will cause the leaves to develop rapidly, resulting in high-quality lettuce.
Watering lettuce early in the morning will reduce the number of hours of leaf wetness and limit foliar diseases. Overwatering, especially in heavy, tight soils, can lead to diseases, soft growth and scalding or burning of the leaf margins.
Fertilize three weeks after transplanting. Lettuce prefers soil that is high in humus, with plenty of compost and a steady supply of nitrogen to keep if growing fast. Use organic alfalfa meal or a slow-release fertilizer.
WEED CONTROL
Weeds are controlled mechanically, manually or chemically. Mechanical weed control can only be practiced before planting because of close spacings.
Weeds are removed by hand hoeing or pulling between plants in the rows. Chemical control can be achieved through the application of propyzamide shortly after sowing, which can last 12 months and longer in the soil.
PEST CONTROL
Like most crops, lettuce is vulnerable to pests. These vary by region and time of year. Fortunately, growing plants off the ground is one of the best ways to avoid pests.
Aphids
Aphids are small, soft-bodied insects that are most commonly green and black in colour, but may also be gray, brown, pink, red, yellow, or lavender. They tend to feed on tender, young growth causing it to appear puckered or deformed.
There are numerous methods of aphid control, including botanical sprays such as insecticidal soap, pyrethrum, rotenone, and horticultural oils. Beneficial insects such as ladybugs will also help to eradicate the pest.
Other major pests of lettuce are Cabbage LoopersCucumber Beetles.
HARVESTING AND STORAGE
Leaf lettuce may be cut whenever it is large enough to use. Cutting every other plant at ground level will give the remaining plants more space for growth.
Leaf lettuce reaches a maximum size (6 to 12 ounces) in 50 to 60 days.
Butterhead varieties form small, loose heads that weigh from 4 to 8 ounces at harvest (60 to 70 days). The innermost leaves, which tend to blanch themselves, are a delicacy.
Cos varieties have an upright growth habit and form a large head. To store lettuce, wash, drip dry and place it in a plastic bag in the refrigerator.
Lettuce keeps best at 32 degrees F and at high (95 percent) humidity.
https://www.agricinfo.com/2018/12/how-to-start-lettuce-farming.html