News Column Tony Bratsch Extension Educator, Horticulture Effingham Extension Center 1209 Wenthe Drive Effingham, IL 62401 Phone: (217) 347-5126 Email: bratsch@uiuc.edu Kill Date: July 30, 2007 Asparagus Beds Need Attention After the Harvest Ends June marks the end of asparagus cutting season. Now is the time to think ahead to next year’s harvest and take measures to improve and maintain vigor in your planting. From now until the first freeze in the fall, asparagus plants are building and storing reserves, and developing the crown buds that will become the spring shoots of 2008. The degree of sugar and carbohydrate build-up achieved this year directly influences the quantity and quality of spears next year. In weakened asparagus beds, spears become small, thin and spindly. This is often a result of cutting too long into the early summer in previous years, and not caring properly for the planting. Usually on a mature, healthy planting, 6 to 8 weeks of cutting is easily tolerated. Low fertility, root and foliage diseases and insect damage can also weaken the planting and be responsible for poor production. Though asparagus is winter hardy, with more shallow plantings, severe and sudden drops in temperatures can damage older crowns. Over time and as plants age, crown depth can decrease as the crowns slowly “creep” upward and become more exposed to sudden soil freezing events. Reduced spear size is not always related to adverse growing conditions. It is also related to the sex of the plant. Asparagus plants are male and female. Female plants have thinner spears and produce red berries. Male plants flower also, but do not fruit, and thus expend less energy on reproduction, instead developing thicker spears, though usually fewer in number. As male plants are preferable, how can the gardener select for them? With new crowns or seed of older varieties such as ‘Mary Washington’, usually a mix of male and female plants occurs, but there is no way to tell the sex of the plants until they flower. Newer “all male” hybrids are now available on the market, and are being widely planted. Developed by breeders in New Jersey, the series of asparagus varieties with ‘Jersey’ in the name are available in most garden catalogs. Look for varieties such as ‘Jersey Knight’, ‘Jersey Giant’, ‘Jersey Supreme and ‘Jersey King’, all of which perform well in the Midwest. In addition to having larger spears, these hybrids have considerable disease tolerance to root rotting and foliar rust diseases. New asparagus beds take several years before abundant, thick spears are produced. To maintain production, good management of the foliage during the summer and fall months is required, with a focus on providing adequate fertility, managing foliar disease and insect damage, and limiting weed pressure that competes with the asparagus plant. A well-planted and maintained asparagus bed should be productive for 20 to 30 years or more. To maintain fertility, a surface application of fertilizer should be applied after the last cutting is made. Apply well rotted compost or manure, covering the soil with 1 to 2 inches deep in a two foot wide area over the row. If manure is not available, apply commercial fertilizer such as 12-12-12 using a cup of material for every 10 feet of row. Avoid contact with emerging shoots and stems to avoid burning. When manure is used, cut chemical fertilizer amounts in half. Research has shown that asparagus responds variably to fertilizer applications. If vigorous growth is occurring, a lighter fertilizer application may be adequate. It may be more efficient to apply some fertilizer in the very early spring prior to first spear emergence, and again after harvest, especially on lighter soil types. Keep in mind that spring and post-harvest fertilizer application will not improve the current season’s crop. Instead it increases growth and vigor of the tops or 'ferns' from now until fall, improving next year’s crop. Good weed control is also essential to maintain vigor in a planting. Herbicides containing trifluralin (Preen™) can be used for control of annual weeds in larger plantings. At one time salt was commonly used to kill weeds in asparagus. Because of its origins near the Mediterranean Sea, asparagus is fairly salt tolerant. However prolonged use of salt leads to deterioration of the physical properties of the soil and a reduction in growth, and is not recommended. Asparagus beetle is a common insect pest of asparagus, as well as Japanese beetles. They should be kept under control for maximum plant growth and production. Insecticides such as carbaryl (Sevin™) and malathion (Fertilome Malacide™) are listed for use on asparagus. Apply when feeding and presence of the beetles is noted. There are also foliar diseases (rust and leaf spot) that can brown and discolor foliage, reducing the capacity of the plant to photosynthesize and build reserves. As noted, the hybrid varieties have some level of resistance. Use a fungicide containing chlorothalonil (Daconil™) at monthly intervals after harvest to help suppress these diseases. Because hybrid plants are larger, initial spacing at planting can be wider (5’-6’ wide rows, plants 18-24” apart), than non-hybrid plants. This not only allows more room for the plants, but increases air movement in the planting which helps reduce foliar disease. Asparagus is an easy and rewarding crop to grow, requiring minimal maintenance to ensure a successful crop from year to year. Attention to fern care during the summer months will return a plentiful harvest of spears next spring. For more information of asparagus and other vegetable crop growing, check out the University of Illinois publication “Vegetable Gardening in the Midwest”, available from your local county Extension office or visit the U of I Extension website “Watch your Garden Grow” at: http://www.urbanext.uiuc.edu/veggies/.