76 MANAGEMENT OF THE FORCING-HOUSE. 



caused by the dying of the lower leaves, but it does reach a 

 marketable size sooner. It is customary to allow the plants 

 to stand as long as they continue to improve, but in case it 

 is desirable to cut before that time it will be found that the 

 sub-irrigated lettuce will be a week to ten days ahead of the 

 other. Should the size to which surface- watered lettuce can 

 be grown be set as a standard, and the sub-irrigated cut 

 when it reaches that size, it will be found that the latter will 

 be ready four to six weeks from the time of planting in the 

 beds, and the surface-watered must be allowed to remain 

 from six to eight weeks to attain the same size Whether 

 we reckon in this manner, or by the actual weight of the 

 crops harvested during the season, there is a gain in one 

 season of about one crop by sub-irrigation. Both the yield 

 and price vary, of course ; but for a house 20 x 100 feet the 

 difference in a single season between surface- and sub-irriga- 

 tion might safely be estimated at from $50 to $100. The 

 latter figure might not be reached, except on very heavy 

 clay soil, and on soil specially adapted to lettuce the dif- 

 ference might be even less than the lowest, but experience 

 has shown that it is more likely to exceed than to fall below 

 $50. The difference is likely to be greater with new begin- 

 ners than with those of experience, as more skill is required 

 to manage a crop by surface- than by sub-irrigation. It is an 

 established fact that good head lettuce cannot be grown on 

 heavy soil by surface watering, and the same is, in a meas- 

 ure, true of all varieties. It is evident, therefore, that sub- 

 irrigation greatly enlarges the possibilities of lettuce culture 

 under glass. It not only makes the work easier for new 

 beginners, but it makes it possible to use soil that would 

 otherwise be precluded. More than that, it solves the prob- 

 lem of meeting competition from the south, which competi- 

 tion bids fair to ruin the business of vegetable forcing at the 

 north, unless improved methods are adopted by northern 

 gardeners." 



Very similar results with lettuce have been secured by 

 Rane, who also found much less trouble with rot in sub- 



