Soil pH in The Home Garden

Iowa soils are very divers and then are the chemical characteristics that make up these soils. Soil ph is one property that can vary widely across the state both naturally and due to crop production inputs. It is besides one of the most price effective and easy to manage territory properties that can be modified to improve establish health and crop production.

Soil ph affects the handiness of nutrients for plant consumption. They may become more available for pant uptake or less available depending on dirt ph. For case, the mircronutrients iron, manganese, and zinc become more available as ph decreases but molybdenum become less available. In Iowa, micronutrient deficiencies such as cast-iron or zinc are frequently due to above optimum land ph and can be corrected by reducing the soil ph rather than adding extra micronutrients to the territory.

Soil ph is the standard of assiduity of hydrogen atoms in solution. The scale has a rate from 0 to 14. Less than 7 is acidic, 7 is neutral, and greater than 7 is considered alkaline or basic. As the dirt ph increases, the act of hydrogen atoms decreases. however, the scale is not analogue. land with a ph of 5.5 is 10 times more acidic than territory with a ph of 6.5 and 100 times more acidic than land with a ph of 7.5. It is authoritative to remember the scale is not analogue when adding amendments to modify soil ph. When modifying soil ph, doubling the amount of sulphur or birdlime will not double the change in soil ph.

Most soils in Iowa have a ph between 5.5 and 7.5, however Iowa soils can be deoxyadenosine monophosphate low as 4.5 or greater than 8.2. The ideal scope for most plants grown in Iowa is 6.0 to 7.0 but some plants like blueberries and azaleas prefer more acidic soils and others like lavender, peony, and salvia prefer more alkaline soils. Further complicating the publish, dirty ph is not a static condition ; it can change over time due to fertilization practices, irrigation, or natural weather. Because of the broad roll of dirt ph found across Iowa and the varying needs of plants, gardeners and farmers often must adjust the dirty ph for optimum plant growth and production.

Soil ph is easily modified in most soils using sulfur or lime. however, before attempting to modify the dirt, collect a dirt sample to determine the existing dirty ph and buffer ph. These territory properties are necessity components to making inform decisions about amending territory ph. Directions for collecting a territory sample can be found in the extension publication Soil Sample Information Sheet for Horticulture Crops ST0011 via the Iowa State University Extension Store.

It is absolutely necessary to make territory ph changes before planting. Lime and sulfur, amendments used to increase and decrease soil ph, respectively, are not water soluble and need to be mechanically incorporated into the dirty with a stool, shovel, or phonograph record to a astuteness of 6 to 8 inches. Once plants are in the grind, it is about impossible to make promote corrections without disturbing the beginning system nor is it fair to amend the dirty below a 6 to 8 column inch depth. Allow the land clock time to change. This is not an instantaneous process and may take weeks or months. When making significant changes to the soil ph before planting perennial crops, it is best to amend the soil, wait 6 months, and recheck the land ph .

Decreasing the Soil pH

elemental sulfur and aluminum sulfate are the most common amendments used to decrease the land ph. elemental sulphur is the safest choice to decrease territory ph ; it is relatively cheap and available via local farming suppliers and garden centers. unfortunately, it is boring to react. elemental sulphur must go through two processes, a biological serve and a chemical serve, before dirt ph is decreased. This much takes 3 to 6 months of warm land temperatures when land biology is active. Aluminum sulfate reacts in the territory identical promptly as it must alone undergo a chemical process. The change in ph happens within days or weeks. however, aluminum sulfate is not an ideal amendment because requires more material than elementary sulphur to reduce the land ph and aluminum is toxic to plants.

Soils that are naturally high in ph or highly buffered will tend to return to their natural state. ammonium sulfate is erstwhile used by commercial growers on these soils because it is slightly soluble and may besides be used as an annual nitrogen source. It is intended as a precaution to help hold the territory pH down within the coveted range. It is not an effective means at reducing the dirty ph post planting nor should it be used to decrease the ph preplant. early fertilizers such as diammonium phosphate, monoammonium phosphate, and urea are acidifying agents that may decrease ph over time or help hold pH down on naturally high ph soils. These fertilizers should not be used to decrease the dirty ph, but are often responsible for the gradual decrease in land ph in commercial farming fields.

Sphagnum peat moss is frequently suggested as a land amendment to decrease land ph. however, most peat moss found in garden centers is neutral or slenderly acidic. merely canadian sphagnum peat moss has a first gear ph of 3.0 to 4.5 and will effectively reduce soil ph. canadian sphagnum peat moss is best used in addition to sulfur applications when build raised beds for acid-loving plants or when bombastic ph adjustments are required.

Three pieces of data are required to determine how much sulphur is necessary to decrease the territory ph : current ph ( from a dirty examination ), prey ph ( what you want the ph to change to ), and territory type. table 1 indicates how much pure elementary sulfur is required per 1000 sq foot to decrease the land ph based upon the existing ph, the target ph, and dirt character.

table 1 : Pounds of sulfur required to decrease land ph to a astuteness of 6 inches per 1000 sq foot .

Soil pH Soil Type
Current Target Sandy Loam Loam Clay Loam
5.0 4.5 4 13 18
5.5 4.5 8 26 37
6.0 4.5 12 38 53
6.5 4.5 15 50 70
7.0 4.5 19 65 88
7.5 4.5 23 75 104
7.0 6.0 8 15 18
7.5 6.0 16 27 31
8.0 6.0 31 44 53
8.5 6.0 48 65 74
7.0 6.5 2 4 74
7.5 6.5 11 20 23
8.0 6.5 28 27 46
8.5 6.5 46 60 69

Increasing the Soil pH

The ph of acidic soil can be raised by incorporating limestone into the soil. Most limestone found in Iowa is a shuffle of calcium and magnesium carbonate although the ratios will vary. Limestone is slow acting but it is relatively cheap and safe to use. Hydrated linden is more reactive and will increase the soil ph faster than birdlime, however it is dangerous to work with.

Two pieces of data are required to determine how much lime is necessary to increase the land ph : current buffer ph ( from a dirt trial ) and target ph ( what you want the ph to change to ). eminence that the calcium oxide table requires buffer pH and not the soil ph from a soil test. Buffer ph results are lone provided on a territory examination report when liming might be needed as determined by the soil lab. postpone 2 lists calcium oxide recommendations in pounds of pure fine calcium carbonate per 1000 sq foot to increase territory ph from its introduce degree to pH 6.5 or 6.9 to a depth of 6 inches. When bulk agricultural calcium oxide is used, extra adjustment are required to correct for atom size and purity.

mesa 2 : Pounds of lime required to increase dirty ph to a depth of 6 inches per 1000 sq foot.

Buffer pH Target Soil pH Buffer pH Target Soil pH
  6.5 6.9   6.5 6.9
7.0 0 25 6.3 96 16
6.9 0 44 6.2 115 177
6.8 14 62 6.1 131 195
6.7 30 80 6.0 147 213
6.6 48 101 5.9 163 232
6.5 64 119 5.8 181 253
6.4 80 138 5.7 197 271

From Table 14 of extension issue Crop Nutrient and Limestone Recommendations in Iowa PM 1688 via the Iowa State University Extension and Outreach Store.


Gypsum is a calcium and sulfur fertilizer that produces no net change on land ph. It is often used as a fertilizer to supply extra calcium or sulfur to the territory when no ph change is desired .


Modifying soil ph is a dull action that requires patience. Always begin the process with a good territory sample distribution to determine the existing soil ph, cushion ph, and cation exchange capacitance. Apply the compulsory amendments and incorporate into the dirt as outlined above. If plant perennial plants, recheck the dirt ph three to six growing season months late to verify that the soil ph has reached the desire range. If it has not, extra amendments may be necessity .


commercial yield and vegetable growers are encouraged to see Managing Soil ph in Horticulture Crops at .

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Category : How To

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