Cool Season Ornamental Grasses start growing early in Spring, once temperatures stay above freezing. Some are evergreen and require little cutting back in the Spring. They often look their best when actively growing in Spring. They flower shortly after Summer arrives and foliage growth will slow down. The higher temperatures and decreased rainfall will cause them to go into partial dormancy and their color will gradually fade. Some of the most attractive cool season grasses that we have are: Calamagrostis x acutiflora 'Karl Foerster' & 'Overdam', Carex, Deschampsia, Helictotrichon sempervirens (BlueOat), Festuca & Sesleria. Cool Season grasses are the first ones for sale in the Spring. When the weather cools they will start growing again. They can be moved in early Fall and have time to root in before the ground freezes.
Warm Season Ornamental Grasses are slow to emerge in Spring and show little signs of growth until soil and air temperatures get quite warm. When it finally gets hot in July they can grow very quickly. They flower later in the season than cool season grasses and a lot of Miscanthus varieties will not flower at all in our climate because our warm season isn't long enough (not always a bad thing if you worry about plants seeding out). Warm season grasses can handle heat & drought better than Cool season grasses. Warm season grasses that we grow include: Andropogon gerardii (Big Bluestem), Boutelouacurtipendula & gracillis, Miscanthus Purpurascens, Miscanthus Giganteus, Miscanthus sinensis varieties, Panicum virgatum (Switchgrass), Pennisetum, Schizachyrium scoparium (Little Bluestem), Sorghastrum nutans (Indian Grass), & Sporobolus heterolepis (Dropseed).
Warm season grass sales start later than Cool season. They shouldn't be moved or divided until they show signs of growth. Since they stop actively growing when it cools down in the fall they shouldn't be moved then. It is also not a good idea to move any grass when they are in flower for that will put them under too much stress. Late Spring to Early Summer is the best time for moving Warm season grasses.