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New Zealand Journal of Agriculture, Volume 82, Issue 6, 15 June 1951, Page 499

thoroughly worked into the soil; this can comprise 2 parts of superphosphate and 1 part of blood and bone (by weight) and may be applied at the rate of lib. per 6ft. of bed (length). Seed should be sown thinly, preferably in rows 6in. apart, as crowding in the bed tends to increase the prevalence of damping off and other diseases and well-spaced . seedlings develop into sturdy plants by the time they are ready to plant out, usually 4 to 6 weeks from seeding. b For raising seedlings under glass the soil should not be too rich or the plants may become too soft and so more susceptible to damping off; for that reason the blood and bone in the fertiliser mixture may be replaced with hnnpdiKt wun ooneaust. . Suitably sized frames are sft. wide by 9ft. long with walls 12in. high at the back and Bin. high in front. These are covered with sliding glass sashes. Plants should be well hardened off, by gradually increasing ventilation each . day, before being transplanted to the field b me When raising seedlings in a propagating house the standard' seed box . 20in. x 12in. x 3in. will be found most convenient. A suitable compost for seedlings is 1 part of loam, 1 part of leaf mould, and 1 part of sharp river sand,. thoroughly mixed and sieved, The boxes should be filled with the prepared compost to within Jin. of the top and firmed ready for sowing. The seed should be sown thinly, approximately 300 seeds to the box, and covered with a thin layer of finely sifted soil. After being watered lightly boxes should be covered with a sheet of glass or paper. The optimum ternperature range for germination and growth of lettuce seedlings is from 50 to 55 degrees F. The seedlings should appear m from 4 to 6 days, when the glass or paper covering must be removed. Young seedlings will be ready for pricking out into other boxes in about 10 days; they should then be spaced IJin. apart each way. A suitable compost for pricking into is of 4 parts of

clean, turfy loam, 2 parts of leaf mould or well-rotted strawy stable manure, and 1 part of sharp sand to which has been added 21b. of superphosphate and 21b. of carbonate of lime per cubic ya^ d of compost. . Care must be taken when pricking n . m J ure the seedlings by squeezing the leaves or stems. The y ou ng plant should be firmed carefully J? the S( ?il Wl th the seed leaves just above soil level. The completed box ma then be watered lightly, using a very fine rose. Before being planted in the field plants should be hardened off by being removed from the glasshouse and placed in a sheltered position outside, . „ , ~ .. „ , , . , *^ n of raising plants in boxes is that they may be cut out in squares when being transplanted and do not receive such a check as plants lifted from beds. r. „ n . '-' ro P Rotation T . . • „ + ,++ „ • ls inadvisable to grow lettuces continually on the same soil, because some of the most serious diseases affecting lettuces are soil borne and continual cropping with lettuces may lead to a serious build up of disease in the soil; field sanitation and crop rotation are methods of preventing this build up. Most of the other vegetables may be used for rotations. Crop rotation is also of importance in maintaining soil fertility, as the different vegetables withdraw varying amounts of different plant foods. c o :| P rfsr) Aration ‘ 5011 re P ar ation Although they will grow on a wide range of soils, lettuces do best on the lighter friable loams. For summer production good moisture-holding qualities are essential unless ample water can be added by irrigation or sprinkler. Because lettuces develop an undesirable bitterness unless grown quickly, it is important that they be grown in good, rich soil or one that has been well fertilised. Green crops and farmyard manures will do much to provide

organic matter and improve the fertility of the soil, but any material should be incorporated sufficiently far ahead of planting of the crop to decompose thoroughly.

The land should be worked to a fine tilth before planting and carbonate of lime applied at the rate of lOcwt. per acre. Pasture seldom proves satisfactory for lettuce growing the first season it is worked and it is preferable to grow some other crop in the first season. If land from pasture has to be used for lettuces in the first season, the initial ploughing and working- up should be done sufficiently far ahead to secure thorough decomposition of the grass roots. Several cultivations will be advisable before planting to reduce weeds, which are often a problem on land from pasture in the first year.

The base application of fertiliser may be - made and worked into the soil with the final cultivation by tine harrows or by shallow discing. The bed is then ready for levelling, which is usually done with chain harrows or levelling board.

Fertilisers

As lettuces must be grown rapidly, an ample food supply should be available, and under most conditions it is necessary to supplement natural supplies by the addition of fertilisers. It is not possible to make recommendations which, will meet all needs; little more than broad recommendations can be given.

The fertiliser mixture should be a complete mixture, that is, it should contain the three principal elements, nitrogen, phosphoric acid, and potassium. The main element required for the growth of lettuces is nitrogen and the proportion of this in any mixture should, be increased or decreased according to the amount of organic matter in the soil and its natural richness.

The following fertiliser mixture may be used in the average market garden: i part of sulphate of ammonia, 4 parts of blood and bone, 1 part of superphosphate, and J part of sulphate or muriate of potash, all by weight. The usual rate of application is 1 ton per acre, except where the previous crop was heavily manured. If growth is slow, especially during winter, when the natural nitrogen supply of the soil is low, a side dressing of nitrate of soda at the rate of 2cwt. per acre will be of advantage. This dressing must be given before hearting begins and care should be taken to see that it does not come in contact with the plants.

Planting

Lettuces are usually grown in beds of 6 rows. The beds are not raised in summer and are spaced Ift. 6in. to 2ft. apart, while rows of plants run lengthwise with 12in. between each row.

For winter and spring production raised beds are used to improve drainage and soil warmth. A common width of bed is 4ft. 6in., but this may be increased to sft. 6in. The rows of plants run crosswise instead of lengthwise as in summer beds and are 12in. apart; 2ft. is allowed between beds.

Sowing Direct in Field Although most growers prefer to raise plants in the nursery bed and transplant, it is not uncommon for lettuce to be sown direct in the field. Field sowing is done between October and March and is advisable only when the area planted is not subject to heavy weed growth. Advantages claimed for this system are the saving of transplanting and watering-in costs, less need for watering during dry weather because the plants being undisturbed have produced longer tap roots, and earlier maturity. The plants are also less likely to bolt than if transplanted. The chief disadvantages of this system are the difficulty of preventing weed growth from overrunning the young plants and the work of thinning the plants, which is done when the young seedlings are approximately 2in. high. Field sowing is done with mechanical seeders using from 1| to 21b. of seed per acre, and the seed is sown from J to jin. deep in rows 12in. apart. Flat Beds When the young seedlings are to be planted on flat beds the lines are marked out 12in. apart using a wooden marker; this is constructed like a large rake with 3 or 6 prongs spaced 12in. apart. The plants, from 40,000 to 45,000 per acre, should be dug carefully from the seed-bed or cold frame and placed carefully in covered boxes, baskets, or trays and carried to the field. It is usual for each planter to take a handful of plants and walk with one foot each side of the row and dibble the plants in 9 to 12in. apart. Care should be taken to see that the plants are not set any deeper than they were in the nursery. Each plant should be firmed securely. . , This work is sometimes done by contract and an experienced worker can set out as many as 1000 plants per hour. If conditions are dry at planting time, the newly set out plants should be watered. After a week in favourable weather the plants should be rooted and show-

ing signs of growth. The crop should be inspected at this stage and where plants have failed new ones should be set out. Raised Beds When planting is done on raised beds lines are drawn across the beds 12in. apart. The planter works from paths each side of the bed and so avoids consolidating the bed by walking on it. Cultivation and Irrigation Because the plants are shallow rooting, deep cultivation should not be done close to the rows. In friable soil not disposed to cracking during the dry weather cultivation should be shallow and only sufficient to control weeds. More frequent and slightly deeper cultivation may be necessary on heavier soils. As lettuces should be grown rapidly and without a check to secure best results, watering is generally necessary during dry weather. The usual method of applying water is by overhead sprinklers, the most favoured type being the revolving sprinkler. Watering should be thorough and sufficiently heavy to last the crop from 5 to 6 days in dry weather; 12,500 gallons of water per acre is equivalent to jin. of rain and this amount can be considered as about the optimum per application for most soils. Lettuces which have begun to heart should not be watered by sprinkler during . bright sunshine, as this may cause scorching. Harvesting and Packing When cutting, the heads should be tested for maturity by a gentle pressure of the palm or back of the hand, not the fingers. Each head should be cut just above the lowest leaves. Lettuces grown in summer should not be harvested during the heat of the day; they will retain their fresh appearance much longer if cut in the early morning while still wet with dew. If lettuces are packed and held overnight before dispatch to market, it is of advantage to sprinkle the heads with water.