March 6, 2010
They were here before the time of Christ. Their ancient relatives grew during the Dinosaur Age. They laugh at disease and floods, and the elders can even be impervious to fire.
Redwood trees are horticultural and historical marvels.
Sequoia sempervirens is the tallest living thing in the world, growing speedily to 300-plus feet in cool, rainy, foggy locations. The key to their success is moisture - lots of it. Winter rains are good and summer fog is even better. When fog isn't present, a grove of redwoods will make its own: a single large tree can transpire up to 500 gallons of water a day. The fog condenses on tree crowns and drips to the earth below to keep roots cool and happy. A redwood's ability to perpetually move this water hundreds of feet straight up from ground to crown is a feat unmatched by even the craftiest of engineers.
Equally amazing is the bark, a spongy epidermis that can be more than a foot thick and that provides fire protection for mature trees. This bark also protects the heartwood, which thanks to its high tannin content, we enjoy for our decks and benches because of its remarkable resistance to fungi, diseases, rot and insect infestations.
This incredible resistance, combined with their love of water, seems to give redwoods an uncanny will to live. Redwoods are one of the few coniferous trees that can actually be buried and survive. Even fallen trees may keep growing. And branches that crack off during torrential winter storms may sail hundreds of feet to the ground, impale the earth, root and sprout a new tree.
Perhaps this will to live is also because of a redwood's affinity to grow in groves. Like people, they're stronger in groups. Redwoods' shallow roots spread out - way out - beyond the width of the branch tips. A single redwood may topple in the wind, but the roots of multiple shoulder-to-shoulder redwoods intertwine, creating a formidably steadfast family of trees.
Unlike people, redwoods do not fear the tick tock of the reproduction clock. The minimum age for seed-bearing trees is 20 years, but the most fertile seeds come from trees that are 60 to hundreds of years old. (Some redwoods do not generate cones, instead putting all their energy into growing tall.)
If anything negative can be said about these magnificent trees, it's that they don't play well with others. They overtop every other species. They compete with their neighbors for sunlight, and they don't lose. This creates a situation in which only shade-tolerant species thrive underneath - until a tree falls and creates a sunny opening. Some would characterize their constant shedding as "messy," but this, of course, is the environment they love and require.
A walk in the woods
Anyone who has ever strolled through Muir Woods knows all about the shady redwood understory environment. The ground is cool and covered with a thick layer of duff, or redwood needles, that acidifies the soil and allows a host of understory plants to thrive. Ferns, huckleberries and rhododendrons love the acidic loamy soil that is created from the constant dropping and decomposition of redwood needles. Larger trees such as Douglas fir and tanbark oaks thrive in the sky-high understory of redwoods, too.
Then there are the intangibles that only a mature grove of redwoods can provide. The squawk of stellar jays, blur of hummingbirds and slimy trail of banana slugs. The fresh scent of new needles juxtaposed against the earthy aroma of rich humus. Sunbeams blinking through the cathedral. Footprints soft and damp. Silence.
Despite their unmatched beauty, it's hard to recommend planting a redwood in your garden. No matter how "cute" those little baby redwoods look at the nursery, their ultimate height and girth make them difficult garden bedfellows, unsuitable for the average suburban plot. If you have a large clearing, or absolutely have your heart set on a redwood, consider one of several cultivated varieties such as Aptos Blue or Soquel that are slower growing. But be careful. A single redwood is not as steady as a grove, and you may be creating an unwelcomed overly shady situation for yourself or a neighbor. And remember, duff doesn't just fall onto the earth. Needles constantly drop on rooftops, patios, neighbor's houses, sidewalks and streets.
For those who already are surrounded by redwoods, here are some tips for gardening at their feet.
- Not too close. Give them room or they'll take what they need anyway.
- Water, water, water. If you live in a hot or nonfoggy area, you will probably have to irrigate until established. They're survivors, but they do not appreciate dry summers or drought.
- Leave the duff. The pile of needles that stacks up beneath redwoods is a natural mulch and soil amendment. Do not rake.
- Do not feed. If you leave the duff, your redwoods will get all the nutrients they need.
- Know your plants. Everything under a redwood must like water, acid soil and part- to full shade.
Here are a few plants worth considering:
- Ferns: Western sword fern (Polystichum munitum) is a natural under redwoods; other good choices include the Western fivefinger fern (Adiantum aleuticum), California maidenhair fern (Adiantum jordani) and giant chain fern (Woodwardia fimbriata).
- Huckleberry (Vaccinium ovatum): an evergreen beauty; slow growing, but worth the wait.
- Inside-out flower (Vancouveria planipetala): delicate, fresh green groundcover.
- Western azalea (Rhododendron occidentale): beautiful white springtime flowers, deciduous.
- Thimbleberry (Rubus parviflorus): woodsy berry, perennial.
- Salmonberry (Rubus spectabilis): large thornless bramble.
- Redwood sorrel (Oxalis oregano): Use with caution. Although this is a common understory plant, it can take over. Use only if you want or need a spreader.
- Wild ginger (Asarum caudatum): evergreen, heart-shaped leaves, groundcover, leaves have spicy aroma when crushed.
- California wild grape (Vitis californica): for groundcover or to climb a fence or other structure, brilliant fall color.
- Spicebush (Calycanthus occidentalis): 5- to 8-foot deciduous shrub, fragrant flowers and leaves.
- Grasslike plants: sedges (Carex spp.), rushes (Juncus spp.) and greater wood rush (Luzula sylvatica).
- Iris (Iris douglasii): native California bulb for a springtime surprise.