Masterpiece Landscaping Blog

March 26, 2010

What is the pH of your landscape garden soil?

Filed under: Uncategorized — glenn @ 11:51 am

What is the pH of your soil?

“What a question.  How would I know?”  might be your immediate response.

Without getting into the details, most of which I no longer remember, a pH “count” refers to the degree of acidity versus alkalinity  of what is being tested, in this case, soil.   A measure resulting at 7.0  is deemed neutral.   The higher the number indicates greater alkalinity, therefore the lower the number the more acid.  It all has to do with hydrogen content. 

Alkaline soils are often called “limey”. 

Some rock, such as limestone outcrops are  much more alkaline than other rock such as granite, slate, or basalt.  As rock  degrades through weathering, the pH of the local soil will be be adjusted accordingly to the benefit of some plants and the detriment of others.

Most soils around the Twin Cities are slightly acidic…6.3 to 6.6….I am guessing.    If I remember my numbers correctly each tenth of an increase is equal to ten times the difference.  In better explanation, 6.5 is ten time more acidic than 6.6, and one hundred time more acidic than 6.7. 

Balsam spruce grow best on soils around pH 5.0.   White pine foliage usually turns yellowish in soils more alkaline than 6.0 and slightly aqua in well fertilized sandier soils of 5.5. 

Acid loving plants include nearly all of the coniferous evergreens except for arborvitaes.  Chamaecyparis and junipers don’t seem to be too fussy.

Other than conifers, rhododendron and azaleas REQUIRE acidic soil, high in organic matter as they cannot live in heavy soils without good drainage.  Magnolias also prefer similar soils. 

Usually there are three items on the market which the home landscape gardener can use to acidify the soil……apply garden sulphur or aluminum sulphate which are NOT fertilizers, and ammonium sulphate which is an acidifier as well as a nitrogen fertilizer.   Ammonium sulphate should probably not be used in the garden after the first of August since fertilizing at that late date might encourage continued fresh growth making the plant more susceptible to winter injury. 

Garden sulphur can be appllied now.  Sprinkle it into the soil at the drip line of the plant.  Aluminum sulphate can be mixed with water or applied dry and watered into the soil.  It becomes quickly available. 

If you have Endless Summer Hydrangeas in you landscape, keep applying light applications of aluminum sulphate beginning in a week or two if you wish the color of the inflorescence to become pink….or mauvish….or blue as you continue to acidify the plant…..over a period of time.

Aluminum sulphate can be lethal to plants if carelessly over used, so govern your applications according to the label.

P.S.  I have never in my thirty six seasons of landscape gardening my property have tested the soil anywhere on my grounds.   There is almost never a need to do so.

2 Comments »

  1. Wow! That’s a raelly neat answer!

    Comment by Leatrice — July 17, 2011 @ 1:01 am

  2. Boy that raelly helps me the heck out.

    Comment by Peerless — July 18, 2011 @ 5:52 pm

RSS feed for comments on this post. TrackBack URL

Leave a comment

You must be logged in to post a comment.