Warm, sandy soils when properly fertilized are preferable for growing the very early crop; sandy loams furnish the best conditions for all classes of lettuce. Head lettuce never thrives in close, compact soils. For this reason the large plantings, in the open as well as under glass, are usually found on sandy soils. Grand Rapids can be grown in almost any soil properly enriched with stable manures. Big Boston is the best of the heading class for soils and conditions adverse to the best results. Some of the largest and most successful plantations of the North and South are in muck soils. Big Boston is almost invariably selected for these lands.
Most of the seed used in this country is grown in California. Professor Tracy reports, in the bulletin previously referred to, that 500 acres are planted in California every year for lettuce seed. The annual harvest in that state amounts to 250,000 pounds of seed. From 30 to 60 plants will produce a pound of seed.
The greatest care should be exercised in the production of lettuce seed. Some of the most careful commercial growers produce their own seed from specially selected plants. In many instances this has been the means of developing strains of superior merit.
The following methods are employed in starting early plants:
(1) Sow in the open ground the latter part of September or earlier in some sections. Transplant in the cold frames in October, and winter like cabbage plants; set in the field early the next spring. This method was formerly employed almost entirely, but it has not been so common in recent years.
(2) Sow in the hotbed or the cold frame 5 to 6 weeks before the ground can be worked in the spring, and set in the open without previous transplanting. The method is not very satisfactory, because it does not result in the strongest plants, and this necessarily delays maturity.
(3) A popular and satisfactory method is to sow in hotbeds or greenhouses, and to transplant, preferably to flats, which may be kept in cold frames until the plants are set in the open ground. The seed should be sown 8 to 10 weeks before the proper date for field planting, the plants being handled in the same manner as cabbage. If space will permit, it is an advantage to plant 2x2 inches apart in the flats rather than closer. To prevent spindling, the seedlings should usually be pricked out in three weeks from sowing. The soil for sowing and transplanting should abound in vegetable matter. Pure muck is probably the best medium, but if this is not available a compost of two parts of good soil, one of sand and one of rotten manure will provide excellent conditions. Mice are very fond of the tender seedlings. They are best guarded against by the use of corn soaked with a solution of strychnine. The plants must be thoroughly hardened before setting in the field if there is danger of hard freezing.
In the preparation of the soil growers should bear in mind that humus is an important constituent and that stable manures can be used with good effects. They help to secure the proper soil structure as well as to add plant food. Rapid growth is essential to crispness and high quality, and so there must be no want of plant food in available forms. High-grade complete fertilizers should be used at the rate of 1,000 pounds to a ton to the acre, depending upon the previous treatment of the land, and supplemented with dressings of nitrate of soda, which can often be applied at the rate of 150 pounds an acre at intervals of 10 days to two weeks after the plants are well established.
Soil preparation should be thorough. Plants that have been well hardened may be set in the open ground as early as cabbage. When planted alone, they are usually set 1 foot apart each way, although 14 inches gives a better chance for cultivation. Seed is sown in the open from early spring until late fall, and all winter in the far South. It is customary to drill in rows about 1 foot apart and to thin to a foot or less. (See Figure 85.) In home gardens the plants are often thinned at first to about 4 inches and later to I foot. This secures much better lettuce than when the seed is sown in beds, all the plants allowed to grow and the mass of leaves cut when wanted for the table. In the Norfolk region the plants are set 10 x 10 in beds with alleys between. With some protection, as a natural forest or a windbreak of hedges or a tight board fence, the plants usually winter in excellent condition. Lettuce is one of the most popular vegetables for companion cropping. See Chapter XXIII (Succession And Companion Cropping). It is also grown in succession on the same ground, several crops being marketed during the season.
Fig. 85. head lettuce on the left. cos lettuce on the right.
Wheel hoes and hand hoes are used frequently. When sowing in the open it is important to use land as free as possible from weed seeds, to avoid unnecessary expense in weeding and cultivating.
Few crops are benefited more than lettuce by irrigation. Crispness and high quality are the results of rapid growth, which is dependent upon a large amount of soil moisture. When the plants are provided with plenty of moisture they are not only more tender and of better quality, but they attain a marketable size much sooner, and the land thus becomes available in less time for another crop.
The half-barrel hamper (Figure 48, b) is the most popular package for shipping lettuce from the South. On Long Island and in Philadelphia County, Pa., barrels are often used. Various styles and sizes of baskets and crates are used on local markets. Refrigerator cars are utilized in shipping lettuce when weather conditions require their use.
An acre of lettuce should cut at least 30,000 heads, but a greater number is often produced. Henderson calls attention to a grower who realized a profit of $1,000 an acre. There are doubtless many small areas near good local markets that do as well. Prices for the shipped product vary greatly from year to year, or at different seasons of the same year. The crop is usually profitable when prices are satisfactory.
The enemies are not generally serious. Plant lice, which are troublesome under glass, sometimes cause injury to the field crop. Blights and other fungous diseases appear from time to time, but their attacks are seldom of a serious character.