Growing Annual Flowers


Luann Finke and Donald H. Steinegger

This Guide discusses using annuals in landscape design, how to select transplants, and proper seeding, planting and cultivating methods.

Annual flowers are a prime source of color that can accent and enliven the home landscape. While flowering trees and shrubs provide short periods of color, annuals begin blooming within a month of planting and continue until frost. The wide range of colors and sizes, and the wide variety of species that are adapted to either sun or shade plantings, make it possible to find an annual flower for almost any setting. For example, they can be used in beds, borders, rock gardens, window boxes, hanging baskets, or as temporary ground covers and fillers.

An annual is defined as a non-woody plant that completes its life cycle in one season, ending with the production of seed. Confusion can arise when an annual plant reseeds itself and appears to have a perennial habit. Or, when plants that are actually perennial bloom one season but fail to overwinter so they appear to be annual plants.

Use in the Landscape

Annual flowers are part of an overall landscape design, so the planting must be evaluated for color, texture, form and mass. Color is a primary consideration in developing a design. In general, a planting design with simple mixtures of color is recommended. Color themes using a variety of related colors, such as red, orange and yellow, or green, blue and purple, or shades of one color, are attractive and popular. Another pleasing effect comes from using complementary colors-those colors found directly opposite each other on a color wheel, such as orange and blue, or purple and yellow. In all cases, be aware of surrounding or backdrop colors to achieve a coordinated overall design.

Plant height is another important design consideration. A flower border typically has the tallest plants in the back, medium height plants in the middle, and the shortest plants in the front. An island planting locates the tallest plants in the middle of the bed, surrounded by plants of decreasing heights.

The style of the annual flower planting should also be compatible with the overall style of your landscape design. A planting can have either a formal or informal design, depending on the arrangements of the planting. Formal designs tend to be made up of geometric lines and symmetry, and have a strong focal point that attracts the eye. In contrast, informal designs typically have curved, flowing lines and natural forms, follow a natural terrain, and create an asymmetrical balance within the planting.

The physical characteristics of the planting site must also be evaluated. A site's sun exposure, wind, soil type, fertility and drainage are factors to consider. Compare site characteristics with specific plant requirements. An annual plant that is adapted to the site conditions grows and flowers more vigorously and has fewer pest problems.

A great advantage of annual flowers is the flexibility they offer in landscape design. A planting can easily be changed each growing season to create an entirely new design. Annual flowers are a source of quick color and can be used as a temporary solution in a problem site.

Seeds and Plants

Many annual flowers, such as marigolds, globe candytuft and zinnias, can be direct-seeded; that is, the seed is planted in the location in which it will be grown all season. Others should be started indoors and transplanted outdoors at the appropriate time. Growing seedlings indoors at home requires proper light and temperature, a sterilized growing medium, and many weeks of careful attention. It is very difficult to produce quality transplants in a home situation, so in many cases the gardener is better off to purchase transplants. Flower transplants are produced using the same methods as for vegetable transplants.

When selecting transplants, look for stocky plants with dense foliage and rich colors. Avoid seedlings that are leggy or dried looking. If possible, check the root system to see that the container is filled with roots. While it is tempting to choose plants that are already blooming, it is better to select those that have not yet bloomed.

Soil Preparation

Prepare a bed for annuals by digging or rototilling 8 to 12 inches deep. Amend the soil with organic matter such as well rotted manure, compost, sphagnum peat or leaf mold. Spread 1 or 2 inches of the organic matter over the soil and incorporate thoroughly to a depth of 6 to 8 inches. Plants will respond to a preplant incorporation of fertilizer. However, do not overfertilize as it can cause excess foliage growth at the expense of flowers. Apply 1 to 2 pounds of fertilizer, such as 5-10-5, per 100 square feet of bed and incorporate. Rake the bed smooth and remove any stones, clods, or old plant debris before planting.


Seeds of annual flowers vary in their hardiness and ability to germinate under certain soil temperatures. Hardy annuals are those that can be direct-seeded in early spring. Tender annuals should not be seeded until the soil has warmed to 60o F to allow good germination. Once the planting bed has been prepared, dig a shallow trench for planting the seed. Distribute the seed in the trench and cover very lightly with vermiculite or some other light soil media. Vermiculite will not crust over as soil often does and allows better establishment of the seedling. Water the planting site with a fine mist to prevent washing out the seed. Keep the bed moist with daily watering until the seeds have germinated. A cloth or board can be placed over the planting site to maintain soil moisture. However, remove it as soon as germination begins. Decrease the frequency of watering as the seeds begin to germinate. Thin out the seedlings before they become crowded.

Planting Transplants

Some annuals tolerate cooler conditions, but most should be planted outdoors only after danger of any frost is past. Try to plant during the coolest part of the day, preferably on a cloudy day. Moisten the plants before removing them from the containers for planting. Keep the soil ball around the roots as you remove the plants from their containers.

If you are using plantable peat pots, make tears in the pots to allow the roots to easily break through the sides. Tear off the top rim of the peat pot if it is to be exposed to the air, or it can act as a wick drawing moisture away from the soil ball and drying out the plant.

Set the plants at the recommended spacing and cover them with soil to the same depth they were in the container. Firm the soil around the roots and water immediately. It is beneficial in promoting root development to water the plants with a starter fertilizer that is high in phosphorus. Make this fertilizer solution by adding 1 tablespoon of fertilizer, such as 10-52-17, to 1 gallon of water.

Most plants respond well to pinching at planting time. By removing the early flowers, the plant's energies can be used to establish the plant rather than support flowers. And, pinching induces branching which will eventually increase the number of flowering stems. Pinch out the first and second set of top leaves for best results.


Annual flowers generally require 1 to 1 1/2 inches of water each week. Be sure that the water is penetrating at least 6 to 8 inches into the soil. Hand watering is generally not adequate to supply sufficient and uniform amounts of water. Soaker hoses or sprinklers are more satisfactory watering methods. Soaker hoses are the most efficient because there is very little runoff, and evaporation and soil compaction are slight. Avoid watering the plants in the evening so that the foliage is dry going into the night. This can help reduce the chance of foliar diseases developing.

An annual flower planting may or may not require additional fertilizing during the growing season. If the soil fertility is low, the plants can be fertilized at a rate of 1/2 to 1 pound of 5-10-5 per 100 square feet every 4 to 6 weeks. Sprinkle the fertilizer lightly along the row and scratch it into the soil. Additional fertilizer may be necessary if the planting is mulched with an organic mulch.

Weeds can be considered the "number one" problem in most annual flower plantings. Cultivation can be used to control weeds, but be careful when weeding not to injure the shallow rooted plants. Cultivate on a regular basis so that the weeds do not get out of control. Mulching is really the best means of weed control. Organic material such as wood chips, hay, leaves or pine needles work well as mulch. Apply 2 to 3 inches of material to the bed. Black plastic can also be used as a mulch. The plastic is anchored down and holes are cut in it for placing the plants. Whatever mulch is used, wait until after the soil has reached at least 60 F before applying it.

Although most weeds in home flower plantings can be adequately controlled with a combination of mulching and cultivation, herbicides are available for use in annual flowers. Dacthal, Treflan, Enide, and Betasan are herbicides labeled for use on some annual flowers. Read the label carefully to determine if the herbicide is safe for use on the specific flower you are growing.

Pinch off faded blooms at least weekly to stimulate blooming throughout the season. Trailing plants, such as fibrous begonia, petunias, pansies and coleus, can be pruned to keep the plants compact and to stimulate additional blooming.

There are relatively few insect and disease problems in annual flowers. However, specific problems will characteristically develop on some plants. Maintaining vigorous growth, having wellspaced plants that receive good air circulation, and planting in a site with good drainage and sun exposure suited to the plant will usually reduce disease problems. Quick identification and applying the proper insecticide or fungicide will minimize the damage of these pests.

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