Choosing the Right Annuals for Your Garden
By The National Gardening Association, Bob Beckstrom, Karan Davis Cutler, Kathleen Fisher, Phillip Giroux, Judy Glattstein, Mike MacCaskey, Bill Marken, Charlie Nardozzi, Sally Roth, Marcia Tatroe, Lance Walheim, and Ann Whitman from Gardening All-in-One For Dummies
To grow annuals, you don’t need to worry about your precise climate zone and temperature extremes as much as you do with permanent plants, such as perennials, trees, and shrubs. The first thing you need to know about any annual that you want to add to your garden is whether it’s a warm-season or a cool-season annual. The difference is vital to planting annuals at the right time of year in your area.
Cool season and warm season are, of course, relative terms. Where summers are cool (such as along the foggy California coast or other overcast climates) you can grow cool-season annuals all summer. Where winters are warm and nearly frost-free (such as in low-elevation Arizona) fall through spring is an ideal time to grow cool-season annuals, such as Iceland poppies and stock, and even some warm-season annuals, such as petunias. In fact, winter and early spring make up the main flower-growing season in Arizona — summer there is too hot to grow any annuals except the most heat-tolerant warm-season varieties.
Cool-season annuals
Cool-season annuals are those that perform best when temperatures are mild — about 70°F (21°C) — days are short, and soil is cool. In most parts of the United States and Canada, these conditions are typical in early spring and early fall. Temperatures may be similarly mild all season in mountain regions or in regions to the far north (or the far south, in the Southern Hemisphere). In some coastal regions, temperatures stay mild year-round. Cool-season annuals can stand varying amounts of frost; some types, in fact, are quite hardy and are actually perennials that live through the winter in many areas. The enemies are hot weather and long days, which cause cool-season annuals to produce fewer blooms and ultimately die. Examples of cool-season favorites are calendulas, pansies, and snapdragons.
In the typical cold-winter/hot-summer climate, the time to plant cool-season annuals is early spring — from four to eight weeks before the typical last frost or as soon as you can work the ground (dig and turn over the soil). Their season ends with the arrival of hot weather, when you can replace them with warm-season annuals. Where summers rarely heat up, many cool-season annuals can thrive all summer right alongside warm-season annuals that don’t demand hot weather.
Warm-season annuals
Warm-season annuals are those that thrive in hot summer weather. Most are tender, and freezing temperatures damage — or destroy — them. Examples are celosias, marigolds, vinca rosea (also called Madagascar periwinkle), and zinnias. Plant these heat-seekers after soil and air temperatures begin to warm up and expect them to reach their peak in midsummer.
The magic date for planting warm-season annuals depends on your climate. Suppose, for example, that you live in the most typical climate, the one that predominates over most of the northern United States, Canada, and northern Europe. This climate typically has cold winters (usually with snow) and warm, often humid summers. In this climate, you can generally grow warm-season annuals from late spring through late summer or early fall. The basic rule for planting is to wait until the danger of frost has passed and the weather has warmed up a bit. Note that some warm-season annuals need more heat than others.
The growing season is the typical number of days between spring’s last frost and fall’s first frost. Generally, the farther north, the shorter the growing season. Growing-season length can be a factor when you’re choosing annuals, especially from seed catalogs, which list the number of days to bloom. Days to bloom is an important number for annuals. It’s usually listed right on the seed packet or in the seed catalog, sometimes right after the plant name. Specifically, this figure refers to the average number of days a plant requires after you plant its seed for the flower to bloom. Your goal is to determine whether a plant’s days-to-bloom average fits comfortably within your growing season.
Gardening Glossary
annuals
Plants that complete their entire life cycle within one growing season. The plant germinates from seed, grows and blooms, and then produces seed and dies.
Gardening Glossary
biennials
A plant that take two growing seasons to complete its life cycle. It germinates and grows leaves and stems in the first year; produces flowers and fruit (seed) in the second, and then dies.
Gardening Glossary
bolt
When a plant flowers or produces seed prematurely.
Gardening Glossary
cold frame
A wooden or concrete block box in which you can grow plants or hold dormant during the cold winter months.
Gardening Glossary
cole crops
A family of vegetables, including broccoli, cabbage, cauliflower, kale, and Brussels sprouts. They thrive in cooler weather.
Gardening Glossary
complete fertilizer
Any fertilizer that contains all three of the primary nutrients, N-P-K (nitrogen, phosphorus, potassium). Phrase is based on regulations governing the fertilizer industry. Does not mean that the fertilizer literally contains everything a plant needs to thrive.
Gardening Glossary
deadheading
The practice of pinching or cutting off spent flowers
Gardening Glossary
evaporative-pad humidifier
A humidifier in which fans blow across a moisture-laden pad that sits in a reservoir of water.
Gardening Glossary
harden off
The process of acclimating plants grown indoors gradually to the brighter light and cooler temperatures of the outside world.
Gardening Glossary
hardiness
The ability of a plant to survive is called its hardiness.
Gardening Glossary
humus
A stable end product of organic-matter decomposition that's believed to increase microbial activity in soil, improve soil structure, and enhance the root development of plants.
Gardening Glossary
Bacillus thuringiensis Bt
An effective bacteria that attacks only the larvae of caterpillar family insects. It is safe to other insects, animals, and humans.
Gardening Glossary
macronutrients
Mineral nutrients that plants need in the largest quantities: nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur.
Gardening Glossary
mulch
Organic or inorganic material placed over the surface of soil, usually directly over the root zone of growing plants. Used to conserve moisture, kill weed seedlings, modify soil temperature, provide attractive covering to garden beds.
Gardening Glossary
organic matter
Once-living stuff like compost, sawdust, animal manure, ground bark, grass clippings, and leaf mold (composted tree leaves). Used to enrich soil and improve soil texture.
Gardening Glossary
perennials
Any plant with a life cycle of three or more years. Herbaceous (non-woody) perennials include flowering plants and herbs, mainly. Woody perennials include trees and shrubs. Longevity depends on the plant and growing conditions.
Gardening Glossary
pH
The measure of soil's acidity. Soil with low pH means it's too acidic; soil with high pH means it's alkaline. Most plants grow best in soil with a pH value between 6.5 and 7.2. Neutral soils measure 7.
Gardening Glossary
photosynthesis
The process through which plants take nutrients from the air and from the water in the soil to produce sugars that fuels the plant's growth.
Gardening Glossary
primary nutrients
Nitrogen, phosphorous, and potassium are the three nutrients plants need in the largest quantities.
Gardening Glossary
root crops
Plants with edible underground roots such as onions, carrots, beets, potatoes, turnips. Most root crops are cold-weather crops.
Gardening Glossary
self-blanching
A type of cauliflower with leaves that naturally curl over the head and exclude light. Requires cool temperatures for leaves to curl effectively.
Gardening Glossary
sets
Small onion bulbs, about 1/2-inch wide, that were started from seed the previous year. Grow onion sets with the pointy end up.
Gardening Glossary
side-dressing
The act of adding a small amount of fertilizer around or "on the side" of plants after they're growing.
Gardening Glossary
succession planting
Planting small, 2-to-4-foot patches of plants every two weeks throughout the growing season so that you can harvest a crop over an extended period of time.
Gardening Glossary
thinning
The act of cutting the least robust seedlings in your garden to give the healthier plants more room to grow.
Gardening Glossary
vining crops
Crops that grow on vines, such as cucumbers, melons, pumpkins, and winter squash. They usually require support (staking, trellising, etc.) to keep them off the ground.
