524 



Gardening for Amateurs 



the surface or the part nearest the water 

 actually approaches a temperature of 200, 

 and there is little danger. Careful regula- 

 tion of the high - pressure steam heat is 

 necessary, and the temperature should 

 never pass beyond 180. In baking soil the 

 danger is even greater, and careful atten- 

 tion is absolutely required. 



A curious point about heat-sterilised soils 

 is that plants grown in it seem to lag and 

 make slow progress at first ; roasted soil 

 is the worst in this respect, but in all cases 

 nitrification eventually becomes more rapid, 

 and the final results are highly satisfactory. 

 For Tomato, Cucumber, and all potting 

 composts sterilisation should be carried out 

 at least a week before the soil is required. 



Sterilisation by Frost. Very great 

 cold is effective in killing many soil pests, 

 and full advantage should be taken of the 

 little frost we get during our winters. 

 Ridged soil, or soil with a lumpy, rough 

 surface, will always be found advisable, 

 and if a garden can be re-ridged occasion- 

 ally the renewed exposure allows a benefi- 

 cent Nature to assist man in his battles 

 with horticultural diseases. 



CHEMICAL METHODS 



Certain soil fumigants may be used when 

 the plants are in full growth, and others 

 should only be placed near roots during 

 winter. To obtain a full, sterilising effect, 

 however, such substances are not powerful 

 enough, hence the milder fumigants will be 

 mentioned in the section on soil pests, and 

 only the more penetrating, drastic chemicals 

 dealt with here. 



Carbon Disulphide. This liquid, a pene- 

 trating sulphur compound, is often used 

 for soil sterilising ; it does no harm to the 

 soil, nor yet to plants, unless it actually 

 comes in contact with their roots. Six-inch 

 holes are dibbled in the garden every 2 feet 

 or so, and into each is poured a tablespoon- 

 ful of the heavy liquid ; the holes are then 

 tightly plugged with soil and the ground 

 covered with mats or bags to keep in the 

 fumes. If the soil is not too compact the 

 method is an excellent one ; the carbon 

 disulphide kills all life and then slowly dissi- 

 pates into the atmosphere as vapour, leav- 

 ing the soil as before, minus the pests. The 



commercial liquid is not too expensive ; it 

 is highly inflammable, and all lights should 

 be kept back from it. A teaspoonful in 

 each large pot of compost is sufficient, 

 although in all cases no harm will come 

 from using much greater amounts. Soil is 

 ready for use three or four days after treat- 

 ment. 



Carbon disulphide can be mixed in all 

 proportions with petroleum or paraffin oil, 

 and if this is done the effects are more pro- 

 longed and lingering, because the fumes 

 do not pass away so readily. Such a mix- 

 ture should only be used for outside work, 

 and some two or three weeks allowed for the 

 fumigant to percolate through the soil. 



Formalin. Formaldehyde, or the com- 

 mercial formalin, which contains over 40 

 per cent, of formaldehyde, is also widely 

 used. This liquid may be mixed with water 

 in all proportions and sprayed on the soil 

 from a watering can, bags or mats being 

 again used to preserve the fumes. A pound 

 of formalin is poured into from 3 to 5 gallons 

 of water, and this liquid is used at least a 

 week before planting. Holes may be dibbled 

 in the garden as before, or the liquid may 

 simply be sprayed on the soil and then more 

 compost spread on top. A tablespoonful of 

 dilute liquid per 6-inch pot of soil is highly 

 effective, although it is quite common 

 practice to spray the pots after they are 

 filled with compost and then to cover 

 them closely with bags. After treatment 

 with formalin, which has a preservative 

 action, soils are generally slow to respond, 

 as when heat is employed for sterilisation. 

 This method is, I believe, the best chemical 

 means for the amateur who wishes to 

 sterilise his soil. 



Naphthaline. The most common fumi- 

 gant in solid form is naphthaline. This 

 substance is obtained as a by-product in 

 the distillation of coal ; it is the main 

 constituent of moth balls, deodorants and 

 the like, and it enters into the constitution 

 of many soil disinfectants and fumigants. 

 The lumps are ground fine, and then mixed 

 with some 15 parts of ground lime ; this 

 is spread along every second or third trench 

 when digging the soil, or in some other way 

 worked well into it ; a handful per 2 yards 

 of trench or from two to three handfuls per 



