Question: Can I kill a new seedling by leaving it out in the weather?
Answer: Great question! Yes, you certainly can. Leaving that new and to be planted baby tree exposed to the drying sun and wind will make quick work of it.
Horticulturist Richard Harris, author of Arboriculture: Care of Trees, Shrubs and Vines in the Landscape, says you should "plant them soon after delivery. The roots must be kept moist and initially protected from temperature increases."

