Understory Management in Organic Tree Fruits and Other Woody Perennials

Weed control and fertility management have been identified as priority research needs by Washington organic orchardists. Mechanical weed control has been the standard practice, often with high cost and potential degradation of soil quality. Mulches can control weeds and improve tree growth and yield, and enhance codling moth mortality with entomopathogenic nematodes (EPN). Living mulches show promise for weed control, soil quality, and fertility benefits but do compete with trees. In a mature orchard trial, wood chip mulch increased the percent of fruit in box size 80 and 88, thus paying for the mulch application. Wood chip mulch also controlled weeds well for two seasons in this trial. A new cultivator, the “Wonder Weeder,” provided less costly weed control than the standard cultivator, but with considerably more weeds than the mulch. No clear effects of tillage on soil quality were measured, but tree growth and yield were reduced by Year 3. In a newly planted trial, wood chip mulch did not control weeds well, but tree growth under mulch was good and similar to the tilled plots. Living mulches generally did provide adequate weed control in the second year after planting, but tree growth was decreased. Vole activity was highest in the living mulches after the first season, but virtually absent in all plots after the second season. The ‘Sandwich’ system treatment showed promise as a compromise between tillage and living mulch, particularly with Galium odoratum as the cover. Tilled plots showed significantly more tree leaning in this untrellised orchard than other treatments, suggesting disruption of tree anchoring but not tree growth. Wood chip mulch did enhance the mortality of codling moth larvae when treated with Steinernema carpocapse and S. Feltiae.

Grant Information

  • Project ID: 004
  • Project Status: Complete


  • Principal Investigator(s): Granatstein, D.
  • Grant Amount: $28,723


  • Principal Investigator(s): Granatstein, D.
  • Investigator(s): Kirby, E., Lacy, L., Mullinix, K.
  • Grant Amount: $31,489


  • Principal Investigator(s): Granatstein, D.
  • Investigator(s): Kirby, E., Lacy, L., Mullinix, K., Wiman, M.
  • Grant Amount: $52,184


  • Principal Investigator(s): Granatstein, D.
  • Investigator(s): Kirby, E., Lacy, L., Mullinix, K., Wiman, M.
  • Grant Amount: $51,591
  • 2006 Progress Report (PDF)


  • Principal Investigator(s): Granatstein, D.
  • Grant Amount: $52,641


Mullinix, K. and Granatstein, D. 2011. Potential nitrogen contributions from legumes in Pacific Northwest apple orchards. Intl. J. Fruit Sci. 11:74-87.

Granatstein, D., Wiman, M., Kirby, E., Mullinix, K. 2010. Sustainability trade-offs in organic orchard floor management. Acta Hort. 873:115-122.

TerAvest, D., J.L. Smith, L. Carpenter-Boggs, L.Hoagland, D. Granatstein, and J.P. Reganold. 2010. Influence of orchard floor management and compost application timing on N partitioning in organically managed apple trees. HortScience. 45:637-642.

Granatstein, D.* and E. Sanchez. 2009. Research knowledge and needs for orchard floor management in organic tree fruit systems. Intl. J. Fruit Science 9:257-281.

Wiman, M.R., E.M. Kirby, D.M. Granatstein,* and T.P. Sullivan. 2009. Cover crops influence meadow vole presence in organic orchards. HortTech 19:558-562.

Hoagland, L., Carpenter-Boggs, L., Granatstein, D.*, Mazzola, M., Smith, J., Peryea, F., and Reganold, J. P. 2008. Orchard floor management effects on nitrogen fertility and soil biological activity in a newly established organic apple orchard. Biol. Fert. Soils 45:11-18.

Granatstein, D.* and K. Mullinix. 2008. Mulching options for Northwest organic and conventional orchards. HortScience 43(1):45-50.

Lacey. L.A., D. Granatstein,* S.P. Arthurs, H. Headrick, and R.F. Fritts Jr. 2006. Use of entomopathogenic nematodes (Steinernematidae) in conjunction with mulches for control of overwintering codling moth (Lepidoptera: Tortricidae). J. Entomol. Sci. 41: 107-119.

Hoagland, L., Carpenter-Boggs, L. Granatstein, D., Mazzola, M., Peryea, F., Smith, J., and Reganold, J. 2007. Nitrogen cycling and partitioning under alternative organic orchard floor management strategies. Proceedings Western Nutrient Management Symposium, Salt Lake City, UT. 7:117-123.

Granatstein, D. 2007. Nitrogen for organic orchards. Proceedings 102nd Annual Meeting Wash. St. Hort. Assoc., Yakima, WA, Dec. 4-6, 2006. p. 58-63.

Additional Funds Leveraged

Granatstein, D., A. Groff, and P. Andrews. 2009. Increasing profitability with organic orchard floor management alternatives. WSDA Specialty Crop Block Grant. $157,526. Granatstein, D. and H. Collins. 2008. Wilbur-Ellis. Nitrogen release from organic by-products with potential fertilizer use. $5,120. Lacey, L. and D. Granatstein. 2006. Entomopathogenic nematodes for codling moth control. Becker Underwood Ltd. $5,000. Cogger, C., A. Bary, D. Granatstein, M. Ostrom. 2003. Assessing soil quality in organic management systems. USDA-SARE $107,696. Granatstein, D. and K. Mullinix. 2003. Alternative weed control in high density orchards. Washington Tree Fruit Research Commission $1500. Granatstein, D. 2003. Spray-on paper mulch for use in organic row crops. Small Planet Foods $3600. Granatstein, D. 2003. NutriSmart, a biological fertilizer. Wilbur-Ellis Co. $2200. Granatstein, D. 2003. Compost to enhance apple tree growth. Soos Creek Organics Inc. $2000. Hogue, E. and D. Granatstein. 2004. Mulching in high-density apple orchards. WA TFRC $1500.