English walnut trees are one of two major varieties of walnut grown in the United States, along with black walnut. Both secrete the toxic substance juglone, which kills most fruit trees. Walnut orchards begin to produce a nut crop within 10 years of establishment, and will produce a high-yield, quality crop 30 years after being planted. Most walnut orchards produce a good crop every three years.
Test your soil prior to planting by digging one quart of soil from up to 10 places in your garden and placing it in a bucket. Mix the soil and remove debris. Allow the soil to dry. Place one cup in a plastic bag and take it to your county extension service. An agent will send the soil to the nearest agricultural college soil testing facility to determine the soil's structure and pH.
Break up the soil of your orchard with a plow to a depth of 12 inches. Spread a 4-inch layer of soil amendments over the soil based on the recommendations of your soil test. Common soil amendments to improve soil for walnut trees include compost, peat moss and composted manure to improve the nutrient content, aeration and drainage. Add sulfur to lower the pH of soil or lime to raise the pH.
Calculate the number of trees you should plant per acre by multiplying the spacing per foot between rows by the spacing per foot within rows. Divide this total by 43,560 square feet per acre to get the number of trees per acre.
Plant nut trees in staggered rows with 300 feet of space surrounding each tree. Thin trees to half this density once the crowns overlap. To plant the trees, open a planting hole in the earth with a shovel that is twice as wide as the tree's rootball, but no deeper. Place the tree's rootball into the hole and fill in around the sides with dirt. Water the tree to remove air pockets, and fill in with more soil.
Cultivate around the trees to remove weeds, grass and brush by rototilling at a depth of less than 6 inches. Continue to keep the orchard weed free for three years until the walnut trees become established. Mowing will not adequately remove competition for water and nutrients. Instead, all weeds, brush and grass must be removed to the root level. After three years, walnut tree canopy and juglone production will be sufficient to kill competing grass and brush.