Xtremehorticulture

Compost’s Role in Landscapes

            Using composts as soil amendments in vegetable gardens has been a no-brainer in the past. We knew it contributed to soil organic matter content. Most vegetables benefited from high levels of soil organic matter so we had no problem adding it to vegetable beds. How much organic matter is enough?             We were taught in school that productive agricultural soils generally contain from 2 to 5% organic matter; some required more than others depending on what was grown. In soils with adequate amounts of organic matter, additions were not needed. But that concept of “one size fits all” when it comes to organic amendments is being challenged and the challengers are winning. We have been educated that the ideal soil has 5% organic matter in it. But is that really enough for all plants?              We were told by scientists that landscape plants would not benefit from the addition of organic matter and that amending the soil at the time of planting was not necessary. Those of us working in arid and desert soils of the West and Southwest quietly challenged that generality and continued to add organic matter like composts to our landscape soils. We could see the benefit. What is a “healthy soil”?             Research during the past 20 years has challenged some of our previous thinking.  In many of our soils, regular additions of organic matter and its decomposition to humus is a necessary step in maintaining a vibrant and “healthy” soil and productive plants. Terms like soil health, soil food webs and soil ecology have become mainstream now. We have always been told that a healthy and vibrant soil contains lots of worms. But does their presence really indicate that’s all that’s needed?             Composting is the process used to convert organic matter into humus and employs many of the same microorganisms that perform the same function in soil. The concepts are very similar. The major difference is that composting provides a greater degree of control over organic matter breakdown than if it were left to an unregulated soil environment.             Fungal and bacterial colonies, earthworms and soil inhabiting insects feed on organic matter. Microbial slimes and gums are produced when organic matter is converted to humus. These byproducts of composting and organic matter breakdown help cement soil particles together. Most mushrooms are “saprophytic” which means they “feed” off of dead things, not living things. The presence of mushrooms in a soil is one sign that something in the soil is decomposing or breaking down. This decomposition is important for recycling, building organic matter and renewing life in the soil.             This altered soil structure is filled with voids that permit the entry, percolation and exchange of water and gases. Improved soil structure or “tilth” is a major benefit from the breakdown of organic matter or the addition of compost.             Byproducts from the decomposition of organic matter and the feeding by soil organisms improve the soil further by altering the soil chemistry and providing organic compounds that stabilize nutrients and assist in chemical reactions necessary for plant survival. Some companies capitalize on the idea that compost adds “life” to soils like this ad campaign by Viragrow, Inc.             When organic matter declines, humus levels decline as well. “Soil health” declines and with it landscape plants suffer. The rate of decline depends on many things including the type of soil, climate, management, nature of the organic matter and other factors. Renewing soil organic matter with compost             If deteriorating soil health is not caught soon enough, large volumes of quality soil organic amendments, such as compost, are needed in a process called soil remediation to bring the soil “back from the dead”. Compost additions to soil improve it by adding aeration, improving water retention while also improving drainage at the same time, and rebuilding life in the soil.             With these additions we see the improvement in soil health reflected in our landscape plants; more vigorous and healthier growth, more tolerance to environmental extremes, small amounts of fertilizer achieve greater results, less water is needed and plants experience fewer pest problems. Managing soil health             As managers of plants we must also manage our soils. The percentage of organic matter in a soil, and thus its humus content, is terribly important. Most soil test results provide the soil organic matter content.             But, is knowing the organic content of our soils enough? To know how much and when to put it back, it is best to know how fast it disappears. Knowing the rate of organic matter decomposition is a powerful management and budgeting tool. With this type of knowledge we understand how often and how much compost to budget for to maintain soil and plant health.              Similar to the composting process, the most powerful external factors controlling the conversion of soil organic matter into humus and its eventual disappearance are moisture and temperature. If soils are kept moist, accumulated soil temperature is the driving force in the loss of soil organic matter. At higher temperatures, soils decompose organic matter faster than in cooler soils. Hot, moist soils need additions of organic matter more often than cool, moist soils. Compost used as a fertilizer             Organic matter releases the nutrients it contains for plant uptake only when it decomposes. By decomposing, plants benefit as well as the macro and microorganisms that live in the soil. Decomposing organic matter also helps support beneficial soil bacteria, fungi and earthworm populations. The decomposition process of organic matter contributes to the breakdown of soil minerals which in turn further release the native plant nutrients they contain. There are enough nutrients in compost that it can act like a fertilizer. Composts very in their nutrient content so it is difficult to claim them as a fertilizer. Some contain more nutrients than others. It depends on the components used in making the compost.             In ways not well understood yet by scientists, the addition

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Wood Mulches for Desert Soils are Remarkable

Desert soil typical of the Las Vegas valley with caliche If you don’t think wood mulch is important for tree growth in desert soils then you need to study this picture of fruit trees in their second year of growth. These are bareroot fruit trees, supplied all the same size, from Dave Wilson Nursery. Fruit and nut trees include plum, pluot, almond, peach and apple. All planted in the same manner in a typical desert soil in Las Vegas. The only difference was the application of wood mulch to the surface of the soil at the time of planting. Not bark mulch, wood mulch that was diverted from landfills and used as a mulch instead and supplied by a tree service company, First Choice Tree Service. This is their second year of growth. The soil is classified as a sandy loam but hard as concrete because it lacked soil organic matter. The pH of the soil was right around 8. The salinity of the soil was over 40 mmhos or dS/m. Boron levels varied but about 8 ppm on an average. This soil was about as bad as any soil can get and still grow something. This is very typical of raw desert soils in the Las Vegas Valley. Wood mulch in the orchard and improved soils How it was done Irrigation was installed using 2 gpm bubblers. Irrigation was bubbler and basin, with a six foot basin surrounding each tree. Holes were dug with picks and shovels four feet in diameter and deep enough only to accomodate the roots of the bareroot trees at planting time. All rocks larger than a baseball were removed and the soil taken from the hole was amended with an equal amount of dairy compost. Before planting all holes were leached to remove some salts with about 20 inches of water applied to each basin. Trees were planted in late January into the basins and watered in as they were backfilled with amended soil. A starter fertilizer, about three pounds of 16-20-0, was mixed with the backfill at the time of planting. All trees were watered thoroughly as they were being planted to remove air pockets. Trees were staked and rabbit protection was provided to the trunks as either paper guards or wire screening. A basin was constructed around each tree and included the 2 gpm bubbler. Basins were about four feet wide. Soil under mulch after three years of tree growth and irrigations Finally a coarse wood mulch, coming from freshly chipped landscape trees in the valley, was applied to a depth of four inches in the basin of half of the trees. Orchard aisles were also covered in wood mulch between trees that were mulched. The trees grew for one complete season with and without wood mulch. This picture was taken two months into the growing season of the second year.

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Trumpet Vine Slow Growth and Leaves with Red Spots

Q. I sent you some pictures of my trumpet vine which I planted as a small plant this last spring.  The plant has barely grown and the leaves have developed red spots all over them.  I believe it has a 2 gph emitter and watered three times a week for 20 minutes. Red spots on leaves of trumpet vine. A. Thanks for giving me such good irrigation information. From this I can estimate you are giving the plant about 7/10 of a gallon each time you water, three times a week. This is probably enough water for this plant when it is small but it will not be enough as it gets larger. If you cannot increase the number of minutes, then I would add a second emitter at the base of the plant. Drip emitter at base of trumpet vine             Trumpet vine is a hardy plant and thrives in most of the country where the soil is good and it gets plenty of water. It loves the heat. In fact, this plant can grow like a weed, extremely aggressive and in some places become invasive.              I don’t think we have to worry about invasiveness here. It is not a desert plant so it will need a little bit of extra care.             I see these red spots on leaves a lot with our fruit trees, particularly peaches. To me it is a sign of stress. There are two things that you should concentrate on to get this plant up and going and these focus on soil improvement and fertilizer. Red spots developing on leaves of peach due to stress.             This plant would benefit from improved soils sold applying a thick layer of surface mulch is going to make a big difference. I don’t know what kind of soil improvement you made at the time of planting but this is a plant which would benefit from a lot of compost added to the soil at planting time.             The organic surface mulch is going to help but I would put down a layer of compost near the plant and just under the mulch. You can get a load of free organic mulch from the UNCE Orchard in North Las Vegas. Once you have solved the soil problem, this plant would benefit with added water as I mentioned.              In late January or early February I would fertilizer with a decent landscape fertilizer and combine that with an application of iron. The best soil applied iron is going to be in the iron chelate form called EDDHA in the ingredients. Make sure it is applied to the drip emitters and watered in with a hose. Peters fertilizer, a good quality plant fertilizer.             In about March, spray the foliage with a good quality foliar fertilizer such as Miracle Gro or Peters. If you follow this advice, you will see some dramatic improvements.

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