Transplanting shock in seedlings can be avoided, if the soil temperature is checked before planting. Most seeds require a warm soil to a depth of at least 3 inches in order to encourage germination. Planting by the calendar disregards weather variations from year to year. Timing planting based on soil temperature helps assure plants get a good start. Plants which have been planted in soil which is too cold exhibit symptoms similar to those planted in soil which has poor nutrient values. Once the soil warms up they begin to grow vigorously, if they have survived the cold conditions.The Soil Thermometer has a durable aluminum casting which measures 3/8 inch x 9 inches. Each thermometer is accompanied by a guide giving the minimum and optimum planting temperatures for many popular vegetables.