The Effect of Vacuum on Walnut Sap Flow

The use of either artificial vacuum with a pump and releaser on 5/16-inch sap lines or, more recently, natural vacuum on 3/16-inch sap lines with adequate slope has been well documented in the maple industry (Perkins, 2010, Wilmot 2007, Wilmot 2014). Every 1-inch Hg vacuum applied to maple lines above 15 inches results in a 5-7% increase in sap yield. High vacuum systems typically apply 24-26 inches Hg, more than doubling maple sap production. Vacuum use, which increases the pressure gradient inside to outside the tree, is especially effective during days when sap flow would normally be marginal. Far less is known about sap flow and vacuum in black walnut (Juglans nigra). Black walnut and maple are anatomically and physiologically very different trees.