Stella Otto: The Backyard Fruit Gardener

Today's Tip: Mow vegetation short around the base of fruit trees and bushes to reduce winter habitat for rodents.

Fruit Gardening — Is Your Soil Right for it?

Once you have made an assess­ment of the cli­matic con­di­tions your fruit trees and bushes may encounter in your loca­tion, another vital fac­tor to con­sider is the soil. Sev­eral char­ac­ter­is­tics of  your soil will have an influ­ence on the pro­duc­tive capac­ity of your fruit gar­den. They include soil type or tex­ture and pH:

First, a good look at your soil tex­ture is in order. If your plant­ing area is flat and small, say a few hun­dred square feet, very likely your soil type and tex­ture will be fairly uni­form through­out. If, how­ever, your area pos­sesses some obvi­ous changes in ele­va­tion or cov­ers sev­eral acres, you may encounter sev­eral dif­fer­ent soil types. Each one may be suit­able to grow­ing dif­fer­ent things. The major soil tex­tures can be gen­er­ally defined as:

  1. sand
  2. loam
  3. clay

Sand, as most of us know it, is made up of fairly large par­ti­cles, rel­a­tively speak­ing. These are weath­ered pieces of min­er­als and still fairly coarse in tex­ture. Large pore spaces for water and oxy­gen are found between sand par­ti­cles. Rel­a­tively lit­tle organic mat­ter is present in a very sandy soil. Water tends to run through sand quite quickly. One place to watch out for sand is right around the foun­da­tion of your house. The sand builders use as back­fill to pro­vide good foun­da­tion drainage is par­tic­u­larly lack­ing in plant nutrients.

Loam soils are com­posed of medium size par­ti­cles. They are a com­bi­na­tion of about 50% weath­ered sand and  up to 25% clay. Silt (very fine par­ti­cles) make up the remain­ing soil par­ti­cle per­cent­age. The over­all tex­ture is finer than sand. The soil holds together as a more cohe­sive mass and has a sub­stan­tially greater capac­ity to hold water and nutri­ents than pure sand does.  These soils are com­monly found where there has been ongo­ing decay of plant mat­ter through nat­ural processes. Well aged com­post com­monly has a loam-like texture.

Clay soils are made up of very small, fine tex­tured, highly weath­ered par­ti­cles. Clay tends to have very high mois­ture hold­ing capac­ity which can some­times become a prob­lem by water– log­ging root areas. Clay par­ti­cles have strong ionic charges and are chem­i­cally attracted to each other. As a result clay soil has a ten­dency to become very hard, almost like cement, if allowed to dry out com­pletely. This hap­pens because its very small par­ti­cles fit so closely together.

Note that at this point the terms soil type and tex­ture have been used in their broad gen­eral sense, as inter­change­able terms. In the tech­ni­cal word of soil sci­ence the term “soil type” actu­ally has a very spe­cific mean­ing. There are many soil types, each unique,  named, and denot­ing a spe­cific per­cent­age makeup of sand, loam, and clay. For pur­poses of a small gar­den it may be inter­est­ing, but not crit­i­cal, to know your spe­cific soil type by name.

Ide­ally, a desir­able fruit gar­den soil will be com­posed of 50% par­ti­cles and 50% pore space — the pore spaces con­tain­ing a bal­ance of half water and half air under the best grow­ing con­di­tions. The par­ti­cle frac­tion typ­i­cally includes up to 5% organic mat­ter, that is decay­ing veg­e­ta­tion or ani­mal mat­ter — often manure. The remain­ing 45% of the par­ti­cle frac­tion is made up of com­bi­na­tions of sand, loam, or clay par­ti­cles as dis­cussed above.

In between the three main soil types are “com­bi­na­tion soils” — the sandy loams and the clay loams. As their names imply, they are a mix­ture of a vary­ing per­cent­age of sand and loam or loam and clay. These are often the best soils for fruit grow­ing as they nor­mally have a bet­ter bal­ance of desir­able char­ac­ter­is­tics. For exam­ple, a sandy loam may have good soil drainage, thanks to the sand por­tion. Yet it will also have a higher avail­able min­eral con­tent and good abil­ity to hold mois­ture due to the organic com­po­nent of the loam. Con­versely, clay loams may have high water hold­ing capac­ity, but do not cement as badly when dry because air space is present between the larger par­ti­cles that make up the loam por­tion. All other fac­tors being equal, a sandy loam will be the most ver­sa­tile for grow­ing a selec­tion of dif­fer­ent fruit. You can per­form a quick, handy “dirty thumbs” test right in the gar­den as a way to esti­mate your soil type. For a more pre­cise mea­sure the “jar sed­i­men­ta­tion test” and soil tri­an­gle can be used.

Soil pH
Here it is — soil pH. Every gar­den­ing book talks about it, but most read­ers are still con­fused by soil pH. It always sounds like chem­istry and quite frankly, it is. For the home gar­dener, it is also not essen­tial to under­stand all the chem­istry involved with pH mea­sure­ment. To keep the expla­na­tion sim­ple, we will stick to the basic ideas you need to under­stand in grow­ing your fruit.

The term “pH” is actu­ally an abbre­vi­a­tion for the phrase “poten­tial hydro­gen.” It is a mea­sure of the amount of avail­able hydro­gen ions in a sam­ple of soil. This mea­sure is used to indi­cate the acid­ity or alka­lin­ity (some­times casu­ally referred to as sweet­ness) of the soil. Know­ing the acid­ity or alka­lin­ity of a soil can be impor­tant because it affects the amount and form of nutri­ents avail­able to the plant.

A scale of 0 to 14 is used to express soil pH. To be suit­able for fruit, it has been gen­er­ally accepted that a soil should have a pH of 6.0 to 7.0; with 6.5 to 6.8 pre­ferred (although at least one fruit crop, the blue­berry, prefers a pH of 4.5 to 5.5.)

Most gar­den cen­ters sell small home pH mea­sure­ment kits, that although not extremely accu­rate, can give you a “ball park” pH read­ing. Another resource for soil test­ing is your local coop­er­a­tive exten­sion ser­vice which can, for a small fee, send your soil sam­ple to a uni­ver­sity lab for test­ing. It is a good idea to take a com­plete soil sam­ple before start­ing your fruit gar­den (or other per­ma­nent plant­ing for that mat­ter,) so that you know what you are work­ing with when you start. It will be unlikely that you will need to repeat this test very often, assum­ing that your ini­tial pH is in an accept­able range and you don’t encounter nutri­tion related prob­lems with the growth of your garden.

For an in-depth look at build­ing a pro­duc­tive soil read Build­ing Soils Nat­u­rally.

©2013. Adapted from the Back­yard Orchardist: A com­plete guide to grow­ing fruit trees in the home gar­den by Stella Otto.