It takes only a few mild days for everyone to get spring fever, and it's a great time get into the garden. Alas the rush to plant summer annuals before the unpredictable spring weather settles into a warm pattern leads to unhappy plants. Perennials and cool weather vegetables are fine in cold soil, but your annuals prefer warm soil to grow.
For gardeners, plants are divided into those that like cool soil and weather and those that demand summertime temperatures. In general, most perennials get a better start if you plant them when mild weather arrives, but before the heat of summer. The soil is cooler and rainfall more plentiful. Most newly planted perennials will even survive a light frost. This is not true for tender annuals such as petunias and basil, which cannot tolerate frost. So the last frost date is an important one on a gardener's calendar. The county extension office can tell you when your average last frost date occurs--it's an average of past 25 years of data and should only be taken as that. Sometimes an unseasonably cold weather front brings later frosts.
The daily air temperature heats up beautifully each spring, but cool nights still prevail, and the soil temperatures take much longer to reach a comfortable level for summer planting. Just because you do not have a frost does not mean you have warm soil, and tender summer annuals will sit and sulk until the days consistently get to 80 degrees when the sun's up and stay above 60 at night. Delay planting your annuals until the warm pattern arrives. Rushing leads to weak plants that are more prone to disease and other problems than robust plants. Planting perennials in cool soil is fine--they will thrive and become much better established. This is critical for shrubs and trees as well, so that they can cope with summer heat and dry conditions.
Spring planting is more successful because rainfall is more consistent. There are many sunny days though, and picking a good day to plant is important. Most commercial plants are grown in protected environments, and planting them when the sun is high in the sky causes stress. Aim for a cloudy day, or wait until the evening air cools slightly so the plant can concentrate on getting established, rather than conserving water. When you have finished your planting, water well unless rainfall is forecast. Continue watching the weather for a few weeks and water if it's dry. The best time to water is early morning, when water doesn't evaporate before seeping into the ground.
Mulch is an important step in spring planting because moisture is retained in the soil rather than evaporating as the day heats up. Mulch also keeps weeds from germinating and competing with your plants for nutrients. Most areas have mulch on sale either in bags or bulk, and there are lots of choices. Put the mulch close to the plant and cover the bed to about a 2-inch depth.
Spring is a great time to plant summer blooming flowers such as cannas, gladiolus and dahlias. These do not need the soil to be as warm as tender annuals, but the bulk of winter moisture should have drained away. One simple test is to take a small handful of soil; if you can squeeze water out, the soil is too wet and you should wait to plant summer bulbs. Cannas, iris and others are usually planted just below the surface. Look for a fuzzy base on dahlias to indicate the bottom, which should be placed down in the hole. For sprouting plants such as cannas, there is no top or base, and these are placed horizontally close to the surface.