EFFECTS OF FREEZES ON CITRUS IN CALIFORNIA 269 



them in place and to press them together, so that the free movement 

 of the air between them was prevented. In some cases earth was 

 thrown up around the base of the trees, so as to cover the lower ends 

 of the stalks a foot or so deep. There were young groves of two-year- 

 old trees wrapped in this way that received little injury except to 

 the exposed foliage of the last season's growth, while near-by groves 

 which were carelessly wrapped or which were left unwrapped were 

 badly frozen. 



One of the most marked cases of benefit from paper wraps was 

 observed in a four-year-old lemon grove, the trunks of which had been 

 scored during the summer preceding the freeze. All the trunks in 

 the lower half of this orchard were well wrapped with paper, but in 

 the upper half (the grove being on a gentle slope with south exposure) 

 no frost injury was expected, and this precaution of wrapping was 

 not taken. In the latter case severe bark-splitting occurred, it being 

 necessary to renew some trees from sprouts; but in the lower and 

 colder portion of the property there was no such injury beneath the 

 paper wraps. The degree of frost injury to the foliage and tops, 

 however, was in indirect proportion to the elevation. It is very 

 essential in wrapping the trunks to get the wrap well down to the 

 ground, and there is no reason why the entire trunk, instead of only 

 the lower half or three-quarters, cannot be protected if wraps of 

 sufficient length are obtained. 



The protectors made of yucca, paraffined paper, tar paper, and the 

 like, open at the top, furnished some protection, but are not equal to 

 good newspaper or cornstalk wrapping. The only serious objection 

 which has been raised to the use of protectors is that, under certain 

 conditions, they favor the development of gum disease. 



When young trees are tightly wrapped as a protection against 

 frost, it is important to remove the wrapping before hot weather, as 

 otherwise serious injury may result. 



Protection ~by Lath-houses, Burlap, or Cloth Coverings. Lath- 

 houses, burlap, or canvas coverings afforded good protection to 

 seed-bed stock up to a few degrees of frost. 



Lath-houses kept the temperatures within them warmer than the 

 temperatures outside. In one instance the temperature near the 

 middle of a large lath-house was 4 degrees higher than the outside 

 temperature. It was found in this case that it was a degree or so 

 warmer at the center of the house than nearer the sides. Even where 

 there was a covering of lath without any sides, the plants beneath the 

 lath were affected much less than those without any covering. Part 

 of the protection of the lath-house is due, doubtless, to the shading 



DIVISION OF SUbtKOPICAL HORTICULTURE 

 COLLEGE OF AGRICULTURE 



FV PAI IPORNIA 



