Potomac Elementary School (PES) began an experiment in February 2000 to determine the effects of planting date upon the germination, survival and growth vigor of Virginia long-leaf pines. The experiment was focused on seeds planted in flats placed in a flooded, solar-heated, passively ventilated enclosure. The intent is to plant seeds at approximately 30-day intervals to determine an optimum time of year from February through May for planting.

The enclosure was built using untreated lumber and crystal clear plastic sheeting. Two side-mounted thermostatic louvered vents provide passive ventilation. Access to the enclosure is provided through a large, top-mounted door that is attached with a piano hinge. Thermometers were placed in the front of the enclosure and at the soil surface to monitor air and soil surface temperature. Figures 1 and 2 show the enclosure.

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   Figure 1. Enclosure (Closed)                                                                          Figure 2. Enclosure (Open)

Originally, it was intended to start planting in January, but deep snow damaged the enclosure and prevented repair and planting for nearly a month. The first seeds were planted on February 21. Eight flats, each containing 45 separate planting cells, were used. An artificial planting mixture of 50% peat moss and 50% sand was used. Figure 3 shows PES students planting the seeds, figure 4 shows two fully planted flats in the enclosure. Note that the seeds were planted vertically, one seed per cell.

Figure 3. February Planting                                                         Figure 4. Two Flats of Long-Leaf Seeds

Two weeks after planting, the first seeds began to germinate, examples are shown in figure 5. The first germination count was performed on March 18, a few days prior to the second planting. Figure 6 shows one flat at this time, figure 7 shows the layout of the February-planted flats. A histogram of germination count of all the February-planted flats is shown in figure 8. Table 1 shows the germination count and rate of each flat as of that date.

               
Figure 5. Seeds at Two Weeks                                                     Figure 6. Seeds at 25 days
 

Figure 7. Layout of February Flats                                              Figure 8. Germination Histogram of February Seeds

                                                                                                                                                               At 25 Days