Hazelnut trees are actually shrubs but are grown in many regions of the United States as trained trees, growing on average to about 15 feet tall. After planting your hazelnut trees, you should see a crop of nuts within four years. Hazelnuts actually bloom in winter, cross-pollinating each other by wind-carried pollen. Plant your hazelnut trees in a moist but well-draining location in full sunlight. Although they can withstand temperatures down to about 16 degrees Fahrenheit, hazelnut trees are best grown in warmer climates where the summer season is at least six months long each year.
Grow your hazelnut trees in groups of twos to ensure cross-pollination and nut production. Plant at least two different hazelnut tree varieties to produce nuts.
Plant your hazelnut trees with less than 50 feet between the cross-pollinating tree varieties, or plant the trees as close as 5 feet apart. Ensure that the soil is deep and well-draining, as the trees' roots need a penetration depth of 6 to 10 feet.
Take a soil sample and have it tested by your local agricultural extension office to determine any nutrient deficiencies in the soil and its pH. Hazelnut trees need slightly acidic to neutral pH soils, so amend the soil with garden sulfur to lower the pH, according to the amounts indicated by your soil test results.
Water your hazelnut trees at least once or twice each week to supplement rainfall during the late spring, summer and early autumn. Perform deep, soaking waterings to moisten the soil thoroughly down to the root zone, at least the top 2 feet of soil around the tree.
Harvest the hazelnuts in late summer and early autumn, when the nuts turn from green to a brownish-hazel color. You can pick the hazelnuts from the trees, preferably before they fall.