FLOWER POT COMPOSITION 151 



composition of the paper fibers. Tliis water-proofing material nnist also be 

 harmless to the root system, a part of which will be in direct contact with 

 the inside wall of the pot. Because of the lack of porosity in a properly made 

 paper flower pot, plants will frequently do better in these paper pots than 

 in the standard clay pots. 



In cooperation with an industrial concern in Massaciiusetts-, a thorough 

 investigation has been made of what the requirements of a paper pot should 

 be to insure proper growth of plants. Growers who were using paper pots, 

 water-proofed with paraffin, claimed that poor growth was obtained in these 

 pots because of an acid condition in the soil resulting from a lack of aeration 

 through the wall of the pot. That this premise probably is not well-fovmded 

 is shown by the fact that plants grt)wn in glass containers have proved to be 

 superior to plants grown in porous containers. In Figure 3 are shown 

 tomato, peppier, and calendula plants growing in i)orous pots (clay) and ex- 

 tremely non-porous containers (jelly glasses). Figure 3 also shows the poor 

 growth obtained in pots made of paraffined paper. It is quite evident that 

 the lack of porosity in the pa})er pot is not a factor that hinders nornu\l 

 growth. Sufficient aeration of the soil may be obtained easily through the 

 surface in the same way that aeration occurs in the field and forest. 



Since porosity is not a factor, attention was directed to the soil tenqiera- 

 ture as affected by the materials used in making plant containers (7). The 

 cooling effect by evaporation from a porous pot was sufficient to maintain a 

 soil temperature 20° F. lower than that of a glass container. The temperature 

 of the soil in a glass container followed closely the fluctuations of tempera- 

 ture of the air of the greenhouse. The tenqierature of the soil mass in a paper 

 pot lagged about 3° F. behind the soil temperature of the glass container. 



Table 3. — Tejiperatures of soil mass in three-inch plant containers of 

 different composition. 



In Table 3 is given the half-hourly readings of soil temperatures obtained 

 from a few types of plant containers. The paper pot, in a warm greenhous'^, 



^ Bird and Son, Kast Walpole, jMassacluisetts. 



