Coast redwood has no taproot at all. Its roots go down only 10 to 13 feet (3 to 4 m), and they spread 60 to 80 feet (20 to 27 m) out from the trunk, per the National Park Service. That is one species with hard numbers behind it. Conifer root systems vary a lot from tree to tree, so do not take redwood as the rule for all of them. A redwood reaches sideways several times as far as it sinks. Wide is the honest word for what you are dealing with. Invasive is a loaded one.
You are probably asking because of a driveway, a drain line, or a fence footing. The useful answer for you is not a yes or a no. It is a measurement, and the one you want is taken across the ground, since that is the direction these figures run. A tree that ends up claiming a circle 160 feet (49 m) wide becomes your planning problem long before it becomes your plumbing problem. A young redwood in a nursery pot gives you no hint of that circle. Get the spacing right on the day you plant and you never have to think about it again.
Three separate observations come with those numbers on redwood roots, and you should keep them apart in your head. The first is the missing taproot. The second is the soil. Annual rainfall in the redwood belt tops 100 inches (254 cm), yet the ground stays poor in nutrients, so the trees live off decaying organic matter. The third is how mature redwoods die. Setting logging aside, windthrow is the most frequent cause.
You will see those three braided into one story about a shallow tree that starves and then topples. The record does not say that. It reports each point on its own, with no cause tying them together, and three solid facts serve you better than one tidy theory.
Scale is what makes the spread worth respecting. A coast redwood may stand 367 feet (112 m) tall and measure 22 feet (7 m) across at the base. All of that sits over a root plate no deeper than about 13 feet (4 m), so the footprint you are planning around is broad and flat rather than deep and narrow.
One more habit catches people out when they try to undo a planting. New sprouts can clone from a stump, from the root system, or from a basal burl. Cut the trunk off and living tissue stays in your soil, ready to push up fresh growth wherever it feels like it. So taking the top off a redwood is not the same job as taking out the redwood. Budget for the difference.
Measure the space you have across the ground before you do anything else. Pace out how wide the mature tree gets, and for a coast redwood that is a circle reaching 60 to 80 feet from the trunk in every direction. Treat that whole circle as ground the tree owns, because shallow tree roots want room sideways and you cannot hand it to them later. Judge conifer root systems by the circle they cover and you will not be caught out in ten years. Then be honest with yourself about your lot. I would not put a redwood on a suburban block, and I would keep any large conifer well clear of a foundation or a paved path you care about.
Every figure here describes coast redwood. It is not a measurement of conifer root systems as a group, and this material carries no solid backing on planting distances or cold hardiness. Your regional extension service publishes both for the trees that grow where you live, so ask them before you dig the hole.
Read the full article: Conifers: Types, Traits, and Hard Numbers
