Planting seasons for herbaceous perennials are divided into spring and autumn in the North. One of the first factors when planting older plants is the blooming period of the species under consideration. As the blooming period is one of great activity above the ground, those plants which bloom late in the season, like Japanese windflowers and chrysanthemums, should be moved in the spring when they can make root growth more quickly and thus recover from the shock. On the other hand, those plants which bloom and mature early are practically dormant in late summer and early autumn. Thus, irises and peonies can be moved safely about September 1st, and will recover quickly and make new roots before cold weather sets in, whereas they are very active in the spring and often do not recover from the shock of being moved at that time unless the work is done very early. These are probably the first sorts fit to move in the autumn season, and other sorts follow along as they mature. The planting season for perennials would open earlier in the spring on a light soil than on a heavy one, both because the ground mellows earlier and because a heavy soil warms up more slowly. The texture of the soil is a factor affecting the planting season of perennials more than it does the other larger-rooted plants, and it is better to delay spring planting until the soil is in good condition to handle and is warm. Thus, the spring perennial season is likely to start later and last longer than that for woody deciduous plants, and also start earlier and stop earlier in the autumn. Pot-grown plants and seedlings can be transplanted at odd seasons whenever the weather is right, but it is generally best to wait till spring for all young herbaceous plants. Thus they are given the whole growing season in which to get established. Care should be taken not to bring tender plants out too early, before they have been hardened off, or too late, when the torrid summer days will wilt them down before they take root.
The spring seeding season for lawn grass starts in the Lower Austral Zone in February, about the middle of the month, and continues to May 1st, but may be shut off by the advent of hot weather as early as March 1st. As one goes farther north, the season does not lengthen very much, but merely opens later, extending from about April 15th to June 1st. Thus, this seeding season, to a great extent, overlaps the planting season and cannot be protracted past the closing date for planting without great risk of the bad effect of hot weather on the young grass. The autumn season starts in the North as early as August 1st, and closes not later than October 1st, but generally by the 15th or 20th of September, thus not overlapping the autumn planting season to any extent. As one goes southward, the season again merely shifts along, so that, in the Upper Austral Zone, it opens about September 15th and closes about November 1st, while in the Lower Austral it is pushed along to October 15th. Here the practice of seeding stops, except for the use of English rye as a green winter carpet, and is superseded by the practice of "sprigging" or planting pieces of Bermuda and St. Augustine grass. This grass planting is commonly done in southern Florida in June, while farther north, and especially in Alabama, it is done through the winter months so as to take advantage of the then abundant rains (See Page 59).
Grass seed sown too early in the autumn and not artificially watered will generally lie dormant until the fall rains start germination, and, likewise, seed sown too late in the autumn or too early in the spring will lie dormant until the ground warms up sufficiently to start sprouting. The grass seeding season is from the time the ground gets warm enough in the spring until it gets too cold in the autumn to start the germination process, but this season is as a matter of practice divided into two parts by the period in the summer when the ground is too dry to start germination and the weather is so hot as to require constant artificial watering, both to start germination of the seed and to keep the young plants alive. It is also generally considered wiser not to seed so late in the autumn, in the North, that the young grass plants will not be well established before freezing weather. These are the factors which influence the establishment of the lawn seeding season dates diagrammatically shown on the chart (Plate III). Making lawns in the South is a process of seeding when adaptable mixtures of northern lawn seed are used, and a process of planting roots when the native Bermuda and St. Augustine grasses are used. Northern grass is seeded in the period from September to January. Italian rye is seeded from October to January, and native grass roots are planted as shown on the chart in stations 21 and 22.
Plate III. A chart to aid in determining the most favourable period for transplanting, and for seeding of lawns in various sections of the United States. Note the long winter periods of the Northern Zones, and the continuous planting seasons of the Southern Zones. It is of great importance to be able to plan ahead and to order plants for delivery at the proper time for any section of the country. These are average seasons resulting from observations of normal seasons during a period of years. For supplementary information refer to Plate No. II on page No. 6.