Light Reduces Poinsettia Root Growth
Roberto G. Lopez, Ph.D., Assistant Professor and Floriculture Extension Specialist, Purdue University
Light penetrating through containers into the rooting substrate is known to inhibit poinsettia root growth (Figure 1). In severe cases, marginal leaf yellowing will occur due to very poor root growth (Figure 2). Therefore, poinsettias, including stock plants, should not be grown in translucent or thin-walled white, gray, green, or terra cotta plastic pots that allow light to penetrate into the substrate. Plants grown in non-translucent black pots have normal root development (Figure 3). In order to determine if your pots are appropriate for poinsettia production, pots should be held up to the sunlight to see if light penetrates.
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Figure 1. Poinsettia with no roots present on the sides of the pot due to light penetration into the translucent white pot.
Figure 2. Light penetration into the translucent terra cotta colored plastic pot results in poor poinsettia root growth and marginal leaf yellowing.
Figure 3. Normal root growth in a poinsettia grown in a non-translucent black plastic pot.