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Apple Scion/Rootstock Selection and Planning

Apple Scion/Rootstock Selection and Planning for Michigan

R.L. Perry and J. Hull
Dept. of Horticulture
Michigan State University
East Lansing, MI 48824
J. M. Clements
Extension Tree Fruit Specialist
University of Massachusetts Amherst
Amherst, MA 01003

Updated January 2008


The training system that an apple (Malus x domestica) grower selects must be one which best maximizes all the resources in making the enterprise a profitable venture. There are many parts to the orchard system decision "puzzle" which must fit together in a complementary arrangement to gain maximum precision and profitability. The most immediate question that must be answered regarding the establishment of a new orchard is spacing. Extension agents and growers often need assistance in determining optimum tree density for sites. Trees planted too close, cause excessive shading and competition for resources results in inadequate light penetration, poor quality fruit, low cropping, excessive labor in pruning to reduce shading impact, etc. Excessive distance results in inefficient planting designs where the land surface is under utilized. In 1989, we made an initial attempt at trying to simplify the decision making process by considering the most important variables and assigning them values (number codes in parentheses) in a formula. Assessments on vigor are derived from rootstock and cultivar trials and field observations. Our experience gained from working with the high density orchards and with new cultivars and rootstocks has encouraged us to frequently update the model. The formula is available on the Michigan State University Department of Horticulture web site for general use by the public, students and extension field agents in an interactive mode (spacing calculator) and below. Still more revision in the future will be necessary as we learn more of the technical intricacies of new rootstocks, cultivars, marketing demands and management constraints.

The primary factors affecting spacing include; scion vigor, rootstock vigor, soil type, irrigation, management system and the interactions that take place between them. This spacing recommendation is only relevant to Michigan sites and for single row arrangement of trees -- use good judjment when applying to other situations. Use the on-line form below (enter values) to calculate in-row tree spacing based on your input:

For the iPhone/Safari Mobile (or simplified version) of this calculator, click here.

Scion Vigor (C)

Example/reference cultivars are listed below for each vigor category (code). Enter the number in parentheses that corresponds with scion vigor:

I. Low vigor spur type varieties (1)

  • Redchief Del. (Campbell), etc.

II. Medium low vigor spur-type and precocious cultivars (2)

  • Empire, Idared, Vallee-Spur, Spur-Rome, Spur-Macs, Scarlet-Ace, Braeburn, Spur-Red Del. (Starkrimson, Starkspur, Sturdee etc.), Honeycrisp, Sansa, etc.

III. Medium vigor (3)

  • Prime Red (Akane), Jonathan, Jonagold, Redcort, Gala, High Early Red Del., Golden Del., Early Red One Red Del., Tydeman's Red, Viking, Jonamac, Goldrush, Suncrisp, etc.

IV. Vigorous (4)

  • Rome, Liberty, Novaspy, Imperial Red Del., Lodi, McIntosh, Starking Red Del., Priscilla, Winesap, Paulared, Spartan, Melrose, Jerseymac, Redfree, Cortland, Wealthy, Top Red Del., Red Prince Red Del., Fuji, GingerGold, etc.

V. High vigor (6)

  • Northern Spy, Granny Smith, Mutsu, Rhode Island Greening, etc.

Rootstock Vigor (R)

Example/reference rootstocks are listed below for each vigor category (code). Enter the number in parentheses that corresponds with selected rootstock vigor:

(0) M.27, P22, G65

(0.5) Mark, M.9 NAKB, Bud.9, G.41, Supporter series 1, 2 & 3

(1) M.9 EMLA, PJ2, RN 29, G.16

(2.5) M.26, Supporter 4, G.935, G.11, G.202

(3) G.30, CG.5087

(5) M.7

(7) MM. 106

(9) MM. 111


Soil (S)

Enter the number in parentheses that corresponds with your soil type:

(0) Sandy or gravelly soil to 4 ft. (droughty)*

(1) Low fertility sandy loam or shallow soil < 3 ft.

(2) Moderate fertility, loam soil

(3) High fertility, clay loam, with good moisture retention (i.e., well drained but with good moisture in low areas)

*refrain from using rootstocks in vigor code 0–1 noted above, unless deployed in super spindle system at over 2000 trees/acre

Irrigation (I)

Enter the number in parentheses that corresponds with your irrigation method:

(0) None

(1) Applied when needed, portable sprinkler etc.

(2) Trickle or microsprinklers deployed to meet plant demands. (Scheduling based on Evaporation Pan, i.e. 'Kenworthy Rule of Thumb,' start watering when growth starts at 1 gal./tree/year of tree age for higher density; or 2 gal./tree/year tree age for low density orchards; both up to 12 years of tree age)

  • note: irrigation highly recommended for rootstocks in vigor codes 0-1 noted above

Management System (M)

Enter the number in parentheses that corresponds with your anticipated management system:

(0) High intensity; winter and summer pruning & spread/tie limbs for first six years; supported trees on dwarf rootstocks*

(1) Medium intensity (Central Leader) -- winter and summer pruning

(3) Low intensity (Central Leader) -- winter pruning only

* For high-density systems, enter the number in parentheses here that corresponds with the following system factors. Otherwise leave as or enter 1.

(0.7) Vertical Axis

(0.6) Slender Spindle

(0.4) Tall Spindle or V-trellis

Finally, enter anticipated tree height in feet:

NOW IN-ROW and ACROSS-ROW Tree Spacing based on above input (assumes North/South row direction):

RESULT: Feet between trees IN-ROW.

RESULT: Feet between trees ACROSS-ROW.

RESULT: Trees per ACRE.

The formula and calculation:

In-row tree spacing.
Scion (C) + Rootstock (R) + Soil (S) + Irrigation (I) + Management System (M)
(where high density systems are applied, multiply sum by factors noted in Management category)

Row spacing width.
North/south direction; 1.3 times expected or projected tree height. (For East/West row direction, use 1.5.) Tall Spindle limited to 10 ft. height.

Example calculations:
Example 1: Idared / M.26, sandy (droughty) soil, drip irrigated, on stakes, expect 12 ft. high tree:
In-row tree spacing = (2 + 2.5 + 1 + 2 + 0) = 7.5 feet
Row spacing = 1.3 x 12 = 15.6 feet
Recommended tree spacing = 7.5 x15.6 ft
Trees per acre = 372

Example 2: McIntosh / MM.106, sandy soil, no irrigation, low intensity, expect 14 ft. high tree:
In-row tree spacing = (4 + 7 + 0 + 0 + 3) = 14 feet
Row spacing = 1.3 x 14 = 18.2 feet
Recommended tree spacing = 14 x18.2 ft
Trees per acre = 171

Ex. 3: Jonagold / M.9 EMLA, fair vigor soil, drip irrigated, Vertical Axis, expect 10 ft. high tree:
In-row tree spacing = (3 + 1 + 2 + 2 + 0) * 0.7 = 5.6 feet
Row spacing = 1.3 x 10 = 13 feet
Recommended tree spacing = 5.6 x13 ft
Trees per acre = 598

Ex. 4: Empire / Mark, vigorous clay loam soil, drip irrig., slender spindle, expect 8 ft. high tree:
In-row tree spacing = (2 + 0.5 + 3 + 2 + 0 ) * 0.6 = 4.5 feet
Row spacing = 1.3 x 8 = 10.4 feet
Recommended tree spacing = 4.5 x 10.4 ft
Trees per acre = 931


For a complete list of references, see the complete publication Apple Scion and Rootstock Selection and Planning for Michigan.

Copyright©2008 Jon Clements and Ron Perry

Jon Clements and Ron Perry
Last Updated: 
September 2012