NURSERY PRACTICE FOR PRAIRIE-PLAINS PLANTING 75 



an impermeable seed coat are preferably spring sown, following the pre- 

 scribed pretreatment of rendering the seed coat permeable. Species 

 possessing no dormancy are preferably spring sown. 



Several guiding principles can be stated with respect to spring 

 sowing. If the seed has had some form of pretreatment involving 

 the absorption of water, such as stratification, water soaking, or 

 acid scarification followed by water soaking, it should be placed in 

 direct contact with moist soil when sown, and the soil kept moist until 

 germination is completed. Such seed should not be sown in dry soil, 

 unless irrigation immediately follows sowing, because the dry soil 

 may absorb moisture from the seed, thereby retarding or delaying 

 germination and thus tending to reduce the viability of the seed. If 

 seed has had no pretreatment, or the pretreatment did not involve 

 the absorption of water, it can be sown in moderately dry soil with 

 no loss in germination or vitality, provided adequate moisture for 

 germination is received in due time. 



Some variation in time of spring sowing is necessary when handling 

 a number of species. Seed that has been in stratification the required 

 period will usually be sown as soon as the ground is in condition and 

 will germinate and grow even though the soil may be comparatively 

 cold. Other species not requiring stratification vary somewhat as 

 to their temperature requirements for germination, and sowing time 

 may be adjusted accordingly. Leguminous species, for example, 

 appear to respond better if their sowing is delayed until the soil has 

 warmed up appreciably. A safe ride to follow for such species is to 

 wait until farmers in the same locality start planting corn. 



Some attention should be paid to past weather records and no 

 sowings should be made so early that seedlings will be up prior to 

 the average date of the last killing frost. Likewise, sowing should 

 not be delayed when conditions are right, since late sowings are ex- 

 posed to the hazard of loss from heat. 



Summer sowing is sometimes resorted to for the production of 

 seedlings of a desired size. For example, sowing of black locust i< 

 often delayed until late June in order to hold down the size of the 

 stock. In the Northern States, certain species, notably Siberian 

 pea-tree, require more than 1 year in the nursery to attain planting 

 size, but if given 2 full years are likely to develop into oversize seed- 

 lings. Sowing of such species is often delayed until midsummer of 

 the first year in order that growth the first season may be retarded. 



Heat injury is the main hazard encountered in summer sowing. 

 Germinating seedlings are quite soft and succulent, and high tempera- 

 tures, especially when associated with high summer winds, burn such 

 seedlings regardless of available soil moisture. Insect attacks also 

 are more serious, and hardening-off is more difficult than with spring 

 sowing. 



Although fall sowing exposes the seed to certain hazards not en- 

 countered in spring sowing, it will produce a larger seedling. It has 

 a further advantage from the nurseryman's viewpoint, in that it does 

 away with the necessity for stratifying and otherwise handling the 

 seed over winter. These advantages are not net gains, however, since 

 fall sowings are subject to a number of dangers that may cause com- 

 plete failure. 



