Water is necessary to initiate the germination process in seeds. As the seed imbibes water, enzymatic reactions within the seed trigger the germination process. Enzymes breakdown the energy stored inside the seed endosperm and this energy is used by the seed embryo for growth. The first visible step in the germination process is the emergence of the radicle (this is the first root)(Figure 1). Next, the coleoptile (an opaque protective sheath) emerges. The coleoptile functions to protect the emerging leaf. Lastly, the green color of the first leaf can be seen as it emerges through the coleoptile. Once the first green leaf emerges, the plant can begin to make its own energy through photosynthesis and it no longer relies on the energy that was stored in the endosperm.
Figure 1. Pictured left to right in the order of the germination process are a newly planted seed, a seed with the radicle emerging, the coleoptile emerging, the leaf emerging through the coleoptile, and the leaf and root elongating.
Once the first irrigation or rainfall occurs after seeding, it is important to keep watering! Seedlings are very susceptible to moisture stress during the first few weeks after seeding (Figure 2). The upper 1 inch of soil should be kept moist with frequent irrigation for the first two or three weeks after planting. Germination will occur in 5 to 14 days depending on the temperature and the species planted (Figure 3).
Figure 2. Tall fescue seedlings emerging in a hydroseeded area. As new seedlings germinate they need to be watered frequently enough to avoid drying.
After the seed germinates and seedlings develop roots into the soil, the lawn can be watered less often. Once established, the lawn should be watered deeply and infrequently only when the plant shows signs of water stress.
Aaron Patton, Turfgrass Extension Specialist