Vegetable Garden Ministry
Newsletter 8/27/20
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SOILS MADE INTERESTING (neilsperry.com)
• Acidity or alkalinity (pH). This is a measure on a scale of 1 (extreme acidity) to 14 (extreme alkalinity). 7.0 is a neutral pH. Almost all cultivated plants will grow better in soils that are slightly below neutral – slightly acidic. The plants that need copious amounts of iron will face extreme challenges in alkaline soils. Iron deficiency will ensue, with characteristic symptoms being yellowed leaves with dark green veins, most prominent on the newest growth first. You deal with alkaline soils by adding sulfur soil acidifier and/or by adding organic matter. However, that’s only practical for relatively small plants like azaleas and gardenias, certainly not for large shade trees. You can also add iron amendments, but only if they’re done in tandem with the soil acidifier.
• Color. Most people don’t think about color as being of much importance. However, dark soils (brown or black) indicate high levels of organic matter. Orange and red soils are almost always acidic. Those pigments come from the presence of soluble iron. White soils are, like beach sand, very porous and quite infertile. Yellow soils suggest poor drainage and are often accompanied by the smell of stagnant, soured ground. You can tell a lot about a soil by its color.
• Fertility. You’ll need a soil test to determine this. However, as mentioned, dark soils are often more fertile, and light-colored soils are generally in need to nutrients. Most clay soils in Texas already have excessive amounts of phosphorus, the middle number of the fertilizer analysis. You can have your soil tested at the Texas A&M Soil Testing Laboratory. http://soiltesting.tamu.edu for a modest fee.
• Organic matter content. There is a neat little fact here: you can add organic matter (peat moss, compost, rotted manure, finely shredded pine bark mulch, etc.) to any type of soil (sand or clay) to improve it. Organic matter opens up tight clays, and it helps sandy soils hold moisture and nutrients. In this one case, one product does all.
Articles & photo submitted by Marco M.
High Alkalinity
On the other hand an excessively limey soil; with a pH of over 8 0, can produce plant disorders. Certain important plant nutrients, particularly iron and magnesium are unavailable to plants if the soil is limey.
If a plant cannot absorb sufficient iron then its leaves will turn yellow and it may become stunted and eventually die. This yellowing is known as lime-induced choruses. Bushes (particularly fruit bushes, roses and hydrangeas) and fruit trees quickly show symptoms of chlorosis if iron is not available. You can, however, cure this condition with annual drenches of a solution called Sequestrene.
Some plants like a limey soil (pH of up to 8 0). Examples of these are members of the cabbage family, and ornamentals such as carnations and pinks, gypsophila, scabious, clematis and trees and shrubs such as beech, hornbeam, box and yew.
Another interesting fact is that hydrangeas produce blue flowers in an acid soil, but pink blooms in alkaline conditions. If the soil is neutral, the blooms will be ‘mauvish’.
Acid soils
To raise the lime content of an acid soil, treat it with a dressing of hydrated lime or ground chalk. Usually this application is made in the winter after digging over the garden. Allow the lime to lie on the surface over the winter and then fork it in in the spring. Do not apply manure and lime in the same winter as they interact unfavorably.
On heavy or clay soils apply lime more generously - as much as 1-lb per sq. yd. at one time - but less frequently than on light or sandy types; lime helps to open up and flocculate (create a good crumb structure) the heavier type of soil.
Community Corner
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