Are Redwood Tree Roots Invasive?

Redwoods are not invasive in the sense of spreading out of control across the countryside. But their roots can be a real problem in a garden. For a tree that can grow taller than almost anything else on Earth, a coast redwood has a surprisingly shallow root system, and it spreads very far. Put one too close to a house, a patio or a sewer line, and conflict is likely.

How redwood roots grow

Oregon State University Extension explains that redwoods have wide-spreading lateral roots instead of a taproot. UC Marin Master Gardeners put numbers on it: considering their mammoth size, redwoods have shallow roots only 6 to 12 feet deep, but those roots extend more than 100 feet from the trunk and intertwine with the roots of other redwoods. That network helps them withstand powerful winds and floods.

The UC Master Gardener Program in Contra Costa County describes the root system as shallow and fibrous, which is why redwoods do best with regular irrigation, especially in their first five years. It recommends watering around the drip line and beyond, where most water uptake happens, not near the trunk.

What redwood roots can damage

A UC ANR Garden Notes article describes what happens when coast redwoods are planted in urban and suburban yards. As the root system extends laterally, it can come into conflict with sidewalks, roads and buildings. The article lists:

• Surface roots that make lawns bumpy.
• Cracked concrete in patios, walkways and sidewalks.
• Disrupted pavement and compromised foundations from expanding roots.
• Damaged underground utilities, with roots infiltrating and clogging water and sewer pipes.

UC Marin Master Gardeners also warn that redwoods planted too close to houses and other structures may affect foundations.

How big a redwood gets

Root problems go hand in hand with size. The UC Contra Costa Master Gardeners note that in its native range a redwood can reach 70 to 90 feet tall and 15 to 30 feet wide in 25 years, and in less favorable conditions about 50 feet in 25 years, eventually reaching 200 feet or more. They add that most redwoods removed from landscapes were not correctly sited.

Other problems near redwoods

Roots are not the only issue in a small yard. UC Marin Master Gardeners list these challenges:

• Plants under a redwood face tough competition for water, light and root space.
• Acidic soil and constant leaf litter make it hard for many plants to grow.
• Needles drop on roofs, patios, sidewalks and neighbors’ property, and clog gutters.
• A tall redwood may block neighbors’ views.

Climate matters too

The UC ANR Garden Notes article explains that coast redwoods depend on cool, moist coastal air and fog, and that redwoods planted in hot inland valleys are often stressed. Its author describes stressed redwoods in a valley neighborhood dropping branches and dried debris in even light wind. OSU Extension adds that although redwood is a water-loving species, long periods of standing water can lead to root disease and decline.

How to plant a redwood without root trouble

• Give it room. Site it with its full mature height and spread in mind, as UC Contra Costa advises, and keep it well away from foundations, patios, driveways, sidewalks and underground utilities.
• Choose the right climate. Redwoods do best in the cool, foggy conditions of their native coast. Ask your county extension office before planting one in a hot, dry area.
• Water deeply, out at the drip line. UC Contra Costa recommends regular irrigation, especially for the first five years, around the drip line and beyond.
• Mulch, but not against the trunk. UC Contra Costa recommends plenty of organic mulch, kept off the trunk and root crown, or letting natural needle duff build up.
• Skip the fertilizer. UC Contra Costa says regular fertilization is typically not necessary.

If a redwood is already too close

Root damage near a house is a job for a certified arborist and, if pipes or foundations are involved, the right contractor. Get professional advice before cutting any large roots. For comparison with another tree known for wide roots, see whether oak tree roots are invasive.

Top photo: Dietmar Rabich, CC BY-SA 4.0, via Wikimedia Commons