Landscaping: Flowering Annuals for Wyoming Karen L. Panter Extension Horticulture Specialist Department of Plant Sciences University of Wyoming B-1170 February 2006 Cooperative Extension Service Author Karen L. Panter, University of Wyoming Extension Horticulture Specialist, Department of Plant Sciences, P.O. Box 3354, Laramie, WY 82071-3354 Layout and Design: Jenna Norfolk, Agricultural Communications and Technology Intern Issued in furtherance of cooperative extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Glen Whipple, director, Cooperative Extension Service, University of Wyoming, Laramie, Wyoming 82071. Persons seeking admission, employment, or access to programs of the University of Wyoming shall be con- sidered without regard to race, color, religion, sex, national origin, disability, age, political belief, veteran status, sexual orientation, and marital or familial status. Persons with disabilities who require alterna- tive means for communication or program information (Braille, large print, audiotape, etc.) should contact their local UW CES Office. To file a complaint, write the UW Employment Practices/Affirmative Action Office, University of Wyoming, 1000 E. University Ave., Dept. 3434, Laramie, WY 82071. or bright splashes of color all summer, Fnothing beats annuals. Though many are technically perennials that simply won’t survive cold Wyoming winters, many are truly “annual.” The botanical definition of an annual plant is one that germinates from seed; grows and develops; forms flowers, fruits, and seeds; and then dies all in one growing season. True annuals include sunflowers while others, like impatiens, are perennial in their native Central America but are treated as annuals here. Annuals are highly important in Wyo- Soil and bed preparation ming gardens and landscapes because of Even though annuals are only in the their diversity in foliage color and texture, ground for one growing season, pre-plant flower color and size, and adaptability. An- soil preparation is still important. Most nual blossoms are quite colorful and plants annual flowers grow best in moderately will bloom all growing season. There are fertile, well-drained soil. Wyoming soils are hundreds of species and cultivars available, often low in organic matter, nitrogen and, most of which will thrive in Wyoming. sometimes, available phosphorus. Some Annual flower gardens require planning have poor drainage and high soluble salts. and care. An annual garden, by its very na- These problems need to be corrected be- ture, is very different from a perennial gar- fore planting. The work involved in proper den. Annuals bloom all summer long and soil preparation will pay dividends every must be replanted each spring and cleaned year. out each fall. Have a soil test done. Contact the local Wyoming’s climate can be stressful for county office of the University of Wyoming many plants. Low rainfall, low humidity, Cooperative Extension Service (UW CES) high wind, and high solar radiation, not for assistance. A test will report the soil to mention late frosts in spring and early texture, organic matter percentage, avail- frosts in fall, can make gardening with an- able phosphorus and nitrogen, pH, soluble nuals a challenge. A short growing season salt level, and lime content. Recommen- often limits plant growth. Plus, local soils dations will be included for fertilizer ap- almost always need improvement to sup- plications, if needed, along with other soil port gardens used each year for annuals. modifications. Most Wyoming soils are heavy clay, but occasionally sandy types occur. The best method for improving either clay or sandy soils is to add good quality organic matter. This can be well-aged compost, peat moss, or any clean, well-composted organic ma- terial. The usual recommendation is to add a layer 2 to 3 inches thick on the top of the Always purchase plants with proper garden bed and then spade or till it in to a labels on them. Labeling should include depth of about 6 inches. With annual gar- a plant’s Latin name, one or more com- dens, this should be done each year. Never mon names, picture, height and width at add sand as a soil amendment. Fertilization maturity, planting spacing, exposure needs, may or may not be necessary, depending fertilizer needs, water requirements, and upon the results of the soil test. any other important information specific to that plant. If a label is not present, choose something else. The vast majority of flowering annuals are not cold tolerant, so wait to plant them until after the last local frost date (see side- bar). Carefully remove each plant from its container or cell pack and plant it no deep- er than it was in the original pot or pack. Circling roots can be gently unwound and root-bound roots can be loosened. Lightly firm the soil around the plant. After plant- ing is complete, water each plant carefully Planting and thoroughly. This does two things: it provides water for the plant in its new Even with annual flowers, it is helpful home, and it settles the soil in around the to have a plan drawn up before plants are root system, minimizing air pockets. purchased. A bit of planning on paper may be beneficial. Always consider the mature height, spread, flower color, water needs, Watering and light requirements of plants. Mass Regular irrigation is recommended for planting groups of plants of one species the best performance of many flowering and color will produce an eye-catching dis- annuals. This is especially important for the play. first week or two as the plant is becoming When purchasing plant material, buy established in the garden. There are no from reputable retailers. Make sure the hard and fast rules of thumb for irrigating plants have been properly cared for by annuals simply because of their great diver- the retailer. Foliage should be healthy and sity. If in doubt, follow instructions on the green; check for signs of insect or disease label or carefully dig down 4 to 6 inches in damage. Also look to see if the roots are the flower bed to determine how dry the healthy and white and that the plant is soil is. If it is moist on top, wait another rooted to the bottom of the container or day. If it is dry all the way down, it is time cell pack. Look for signs of stress including to water thoroughly. Infrequent, thorough, leaf tip burning or wilting, which may indi- deep watering is always preferred over fre- cate inadequate watering. quent, shallow irrigations. Try to water in the morning; watering at night leaves foli- age wet which can foster disease develop- ment. It is helpful to plant annuals with similar An excellent option is drip irrigation. Many water requirements together in “zones.” types are available today that will afford Those requiring little additional water thorough coverage with little evaporation, should be planted together, those requir- however, a drip system requires mainte- ing moderate moisture should be in the nance as emitters will sometimes clog. Re- same zone, and those with high water re- placement is usually necessary after a few quirements should be in their own zone. years because the tubing will break down This makes it much easier to water plants over time with Wyoming’s high solar radia- according to their needs, especially if an tion and rapid temperature fluctuations. automated system is used. Soaker hoses are another good option. Watering can be accomplished in sev- These can be hidden under mulch and may eral ways. Hand watering is probably the last somewhat longer than drip hoses. most inefficient, but many municipalities Mulching require this method during periods of Using mulches during the growing drought. The reason is gardeners won’t ac- season will slow the loss of water, prevent cidentally forget to turn the sprinkler off if soil drying and cracking, reduce weak they are the sprinkler. plant growth, prevent soil splashing, and provide a neat and well-kept appearance. Many kinds of mulch are available includ- ing organic types such as bark chunks, pine needles, ground corn cobs, wood chips, or compost. Organic mulches are beneficial Setting a hose and sprinkler out for a in that they return nutrients to the soil as specified amount of time is also acceptable they break down. Be aware that some, like but can lead to over- or under-irrigation. pine needles or any small organic matter, Automatic sprinkler systems set up for may blow away in high winds. Mulch must turf areas may also work, but care must be allow water and oxygen to penetrate into taken to make sure the garden area is cov- the soil below, and it should decompose ered. Unfortunately, this type of watering slowly. A layer 2 inches thick is ideal. is usually on a schedule rather than based on plant needs. Learn how to set or reset the timer as needed throughout the grow- ing season. There are disadvantages to organic mulch- es. In some locations in Wyoming, the soil may stay too cool under mulch. With cool soil, root growth may be inhibited which in turn limits shoot growth. This may be a Fertilizing problem particularly with annual vegetable Annuals differ widely in their fertiliza- crops that may then mature too late in the tion needs. The label on a plant should growing season. If cool soils are a problem, state the fertilizer needs of the plant in wait until the sun has warmed the soil in the container. A soil test will provide the late spring to apply mulch. Also, certain information necessary to determine if the pests like slugs may hide in some mulches. flower bed needs any nutrients. If fertil- Inorganic mulches are also available izer is needed, there are many acceptable but are not as highly recommended.