Determine Your Last Frost Date
There are three things all gardeners should know about their landscapes: the USDA Hardiness Zone, average last frost date in spring, and average first frost date in fall.
The hardiness zone denotes the average minimum winter temperature, so it helps determine which plants will be winter hardy where. It's just one tool to use in choosing plants because it doesn't take any other factors, such as high temperatures or humidity, into consideration.
Average frost dates give you an indication of when it's safe to plant. The average last frost date in spring signifies with a certain probability (perhaps 90 percent) that you won't get a frost after that date. That doesn't mean you won't get a frost, just that you probably won't. You'll often see instructions to transplant tomatoes outdoors after the last frost date, or to start seeds six weeks before your last frost date, so this is vital information.
The average first frost date in fall reminds you that you need to be prepared to cover tender plants if you hope to keep them going. (It's not uncommon to get one hard frost followed by weeks of frost-free weather.) It also helps you determine if your growing season is long enough for certain crops. The number of days between your last spring and first fall frosts is your frost-free growing season.
The easiest way to get this information is to ask someone. Experienced gardeners will know these facts off the top of their heads -- it's so important to successful growing. Or you can contact your Extension agent or visit the Web sites below. Note that maps don't take into account local microclimates, or variations over small distances due to elevation or proximity to lakes, so it pays to doublecheck with a gardener.
Freeze/Frost Maps from the National Climatic Data Center
USDA Hardiness Zone Map
Favorite or New Plant
To me the most important characteristics of an annual flower are beauty (of course), disease resistance, and tolerance for a range of conditions; African daisies fit the bill.
This common name is used to refer to more than one plant -- both Arctotis and Osteospermum species. Fortunately, these two have similar traits: they tolerate dry soils as well as both heat and light frosts, and they do well in containers. The Arctotis species I've seen are yellow or orange -- although they are available in a range of colors -- and they grow to a height of about a foot and a half. The Osteospermum are usually white, blue, or purple, with striking blue centers. They are taller than Arctotis, growing from 2 to 5 feet tall.
Both plants have very attractive satiny-shiny petals. The plants I've grown have tended to be a little rangy and sprawling, so plant them where this characteristic won't be a problem. I like to plant the shorter varieties in a container where they cascade over the sides and soften the look of more "prim and proper" upright plants such as salvia.