The seedling I started from the old black walnut along my back fence line sat at ankle height through its first summer. The stem grew maybe an inch. I pulled it halfway out of the ground one evening, sure the thing was a dud. By spring the young stem shot past my knee, then my waist, once the taproot ran deep. That slow start hides the true black walnut growth rate. On rich, moist ground a young tree can add 3 to 4 feet of height in one year.
That first-year lull throws people off. The tree pours its early energy into a deep taproot before the top puts on much height. So the black walnut growth speed you see above ground trails what your tree does below for a year or two. Once the roots lock in, the trunk climbs fast. My own seedling did just that. By the third year the tree stood taller than me.
On deep, moist soil with full sun, your young tree can add 3 to 4 feet (about 1 meter) of height each year. That pace holds through the early years while the crown fills out. The first season stays the exception. The taproot takes most of the plant's energy before the top ever stretches. That is why year one looks so flat.
You can push young black walnut growth toward the top of that range with the right spot. These trees want full sun for most of the day and roots that never sit in dry ground. Crowd the base with weeds or lawn grass and the yearly height gain drops off. Give the trunk clear sky overhead, since even a few hours of shade each day can shave off yearly growth. Black walnut also puts out juglone, a compound that stunts many nearby plants. Keep tender flowers and vegetables well clear of the roots.
Poor ground tells a different story. On thin, dry, or packed soil, the same tree might add only 1 to 2 feet a year. Shade slows the pace too, since black walnut is a sun lover that sulks under taller trees. A late spring frost can nip new growth and cost you a season of gain. Black walnut handles USDA zones 4 through 9, and the fastest growth shows up in the warm, damp parts of that range.
Watch the first two or three years for the real signal. A young black walnut that gains a foot or more each spring after year one is on track. Keep a ring of bare soil about 3 feet wide around the trunk so grass and weeds do not steal your tree's water. Mulch that ring, but hold the mulch back a few inches from the bark. Deep, slow watering once a week beats a light daily sprinkle every time.
That black walnut growth rate is quick for a hardwood, but timber is still a long wait. The USDA Forest Service puts quality sawlogs at about 30 to 35 years and veneer-size logs at 40 to 50 years. So the height comes fast, though a timber tree is one you grow for your kids. Even so, a black walnut moves faster than most other hardwood trees you could plant for wood.
Give your young tree full sun, deep moist soil, and a weed-free ring of open space. Do that and the tree reaches the faster end of the range. Water the tree through dry spells for the first two summers while the roots set. After that your walnut runs on its own. Give the tree room to spread, since a grown black walnut can top 70 feet and hates a crowd.
Read the full article: Black Walnut Tree: Growing, Nuts, and Value
