210 VEGETABLE FORCING 



be made to determine the merits of the seed. Germina- 

 tion trials should be made from time to time, and the seed 

 may be sown thicker, if necessary, in order to obtain a 

 satisfactory stand of plants. 



Soil. Most of the large lettuce-forcing establishments 

 are located where the soil contains considerable sand, 

 and this is especially true regarding greenhouses devoted 

 to the culture of head lettuce. Cos lettuce seems also to 

 require soil that contains a fairly large percentage of 

 sand. Grand Rapids lettuce is grown with entire success 

 in practically all classes of soils, including the heaviest 

 with the smallest proportion of sand. The general ad- 

 vantages of sand for greenhouse use have been discussed 

 in Chapters III and V, and these should be fully con- 

 sidered in connection with the selection and preparation 

 of soils for the forcing of lettuce. Greater weight of 

 Grand Rapids may be obtained in heavy soils, but, not- 

 withstanding this fact, growers prefer soils that are not 

 too heavy. 



For the production of head lettuce, the soil must be 

 well aerated. This can be accomplished to a great ex- 

 tent by the liberal use of stable manure and sometimes 

 by mixing muck with the soil. Experienced growers, 

 however, claim that one or both of these materials cannot 

 entirely take the place of sand. An open, porous soil is 

 essential, though it is possible to make it too light and 

 fluffy. 



Beach made some interesting experiments at the New 

 York Station; they were reported in Bulletin 146. Soils 

 of various composition were used, but reference will be 

 made to only two. What is referred to as the Geneva 

 clay loam contained 3.32 per cent fine gravel, 5.20 per 

 cent coarse sand, 20.71 per cent medium sand, 43.43 per 

 cent fine sand, 0.94 per cent very fine sand, 7.96 per cent 

 silt, 1.64 per cent fine silt and 9.86 per cent clay. The 

 Geneva sandy loam contained 0.51 per cent fine gravel, 

 0.69 per cent coarse sand, 9.49 per cent medium sand, 



