AERATION OF POTTING MEDIA AND PLANT GROWTH

Providing optimum aeration for plants grown in small pots is a primary concern in the development of potting media. Aeration is defined as the percentage by volume of air-filled pores in a medium after it has been saturated with water and allowed to drain. This study describes how the physical properties of media, as well as the growth of potted plants, varied with changes in media aeration. A 1:1 (vol/vol) peat-vermiculite potting medium was adjusted to aerations of 1.0, 2.2, 5.0, 11.3, 13.3, 20.0, and 33.6%/vol by altering the particle size of the two constituents. Total pore space remained constant as aeration increased, but total moisture-holding capacity declined linearly. Water held above a matric potential of −30 cb increased slightly until aeration reached 10 to 15% and then declined. Water held below a matric potential of −30 cb decreased curvilin-early with increasing aeration. Four potted plants, begonia, coleus, impatiens and schefflera were grown in media with the seven different aerations. Although the plants varied in their sensitivity to aeration, plant growth was most limited when aeration was 5.0%/vol and below. Plants generally grew best in the aeration range of 11.3 to 20.0%/vol with a slight decrease in growth at the highest aeration of 33.6%/vol.