By Susanne von Rosenberg, UC Master Gardener of Napa County
If you're like most gardeners, you always enjoy learning something new. I recently started learning about mast seeding. I already knew that oak trees tend to have light crops some years and heavy crops other years, but I didn't realize that many other trees do the same thing.
According to the Encyclopedia Britannica, mast seeding is defined as “the production of many seeds by a plant every two or more years in regional synchrony with other plants of the same species.” Even in mast years, the plant produces seed, but there is an obvious difference in seed production between a mast year and a regular year. Mast seeding occurs on every continent except Antarctica, and the regional synchronization can extend thousands of kilometers.
What fascinates me about mast seeding is that trees (or other plants) of one species are all on the same schedule regionally and that botanists still don't know why mast seeding evolved. We know a lot about how mast seeding affects the forest ecology but only have theories about why trees and other plants behave this way.
One theory is predator satiation. If a group of plants produces a huge number of seeds, perhaps predators (hungry squirrels, birds or humans, for example) will miss some because there is so much to eat. That means that every few years, some seeds will survive and reproduce. If trees were to produce an even, but smaller, number of seeds every year, predators might eat them all.
Another theory is that mast seeding is climate driven. Certain weather conditions are favorable to ripening seeds, and the trees detect those patterns and behave accordingly.
A third theory is that trees need to store up sufficient carbohydrates in their roots to support seed production. This theory was previously considered unlikely because mast seeding is a regional phenomenon. If carbohydrate storage is the trigger, then trees that are in prime growing locations with plenty of light and water should be able to store more carbohydrates and produce seed more often than trees in shadier or drier locations.
More recently, however, science has shown that trees are linked by mycorrhizal fungi networks that allow them to exchange carbohydrates. Mycorrhizal fungi form a symbiotic relationship with trees. They colonize the tree roots and receive carbohydrates while providing nutrients and water from the soil. Mycorrhizal fungi extend much farther than a tree's roots. So the third theory is potentially valid again.
A fourth theory is that mast seeding makes for more efficient pollination. Most mast-seeding plants are wind pollinated; when more pollen is released, the odds of fertilization increase. It's nice to know that we still have a lot to learn about plants.
Fortunately, we don't have to know why plants mast seed to understand the effects on ecology. Many animals, including large creatures such as bears and hooved mammals, rely on mast seeding, as do many small rodents and birds.
Because mast seeding is irregular and relatively unpredictable, studying the response of wildlife is challenging. Until recently, researchers assumed that a bumper crop of seeds would increase the breeding success of small mammals (mainly rodents) and attract more birds. Consequently, larger animals would also be drawn to the area due to the greater availability of prey.
A meta-analysis covering nearly 200 other studies found the expected response for small mammals and birds but found that larger predators were not necessarily drawn into a mast area, most likely because they have access to a large habitat.
Mast seeding isn't limited to acorns and nuts. Bamboo is also subject to mast seeding. One generation of bamboo can live up to 100 years before all the bamboo in the same vicinity flowers and dies in the same year.
Other plants that are considered mast plants include American persimmon, coffee berry, the dogwood family, the buckeye family, Mariposa manzanita, the mulberry family, blueberries and the elderberry family.
To create more effective habitat in your garden, you can plant mast-seeding plants in a hedgerow or small wooded area. If you keep chickens or pigs, you can improve their diets by planting mast-seeding plants. And if you like to birdwatch, a mast-seeding year may increase your chances of seeing interesting birds.
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By Susanne von Rosenberg, UC Master Gardener of Napa County
One of the challenges many gardeners face is how to make shady spots look good. Fortunately, many beautiful, flowering native plants thrive in shade.
When you are planning your shade garden, analyze what kind of shade you're dealing with. Is it deep, all-day shade, such as in a redwood or pine forest? Do you have full shade for part of the day from a fence or other structure, and then sun the rest of the day? Perhaps you have dappled shade from leafy trees with loose foliage or a trellis?
Different plants are appropriate for each type of shade. Also, do you have dry or moist shade? If your shady area has moist soil, you have the most choices. Even if you have dry shade, though, as many of us do, there are lovely, colorful choices.
Native plants suitable for shady areas range from low-growing ground covers to understory trees, such as dogwoods, that can grow up to 15 feet tall. Some are even deer resistant. To expand your options in dry shade areas, you can provide drip irrigation for plants needing some supplemental water. It's also a good idea to mulch your shade garden toward the end of the rainy season to retain as much soil moisture as possible.
For ground covers for dry areas, consider coyote mint (Monardella villosa) and hummingbird sage (Salvia spathacea). Coyote mint grows one to two feet tall and has a light minty fragrance with light purple globe-shaped flowers. Butterfly mint bush (Monardella subglabra) has deeper purple flowers. Hummingbird sage ranges in height from a few inches tall to those with flower spikes six feet tall. The flowers are typically red or pink.
Wild ginger (Asarum caudatum) and wood strawberries (Fragaria californica) are more suited to moist areas, but both can do well in dryer areas with a little supplemental water. Wood strawberry plants grow four to eight inches tall. The fruits are small but delicious. Wild ginger benefits from a rinse every so often in summer to simulate the fog drip of its native coastal forest habitat. Wild ginger has heart-shaped dark green leaves and unusual flowers. It has a light ginger-like fragrance, and reportedly the roots can be used as ginger.
Yerba buena (Satureja douglasii) has similar growing requirements to wild ginger. It grows four to eight inches tall and has small white flowers. It is lightly fragrant and makes a lovely herbal tea. Yerba Buena Island in the San Francisco Bay was named for its large areas of Satureja douglasii.
Many native bushy plants are adapted to shade. California monkeyflower, many currants and gooseberries (Ribes spp.) and cream bush (Holodiscus discolor) are all great choices. There are two genuses of California monkeyflower\s, diplacus and mimulus. Diplacus species are adapted to dry rocky slopes and therefore drought tolerant. Mimulus species are adapted to moist locations and need consistent moisture. Both come in a range of blossom colors, including yellow, white and red.
Our native ribes include species that flower in white, pink, yellow, and maroon with white. With sufficient water, ribes plants will grow between five and eight feet tall. I have a golden (yellow-flowered) and a pink-flowered currant bush in my yard. They bloom in spring and are gorgeous. The fruit is edible.
Ribes are summer-deciduous, meaning that if they do not get enough water, they will shed their leaves in the summer. You can plant them 10 to 15 feet from an irrigated area, and that will supply enough water to let them keep their leaves.
Cream bush (also called ocean spray and California spiraea) grows up to 6 feet tall and has beautiful 5-inch-long clusters of white flowers. I've added it to my list of plants to try. The growing notes caution that it has a lovely fragrance from 20 to 30 feet away, but that it smells like “old newspapers” close up. While I'm still trying to puzzle out how this is possible, I would definitely follow the recommendation to plant it 20 or more feet away from your house and garden areas you hang out in.
Finally consider native honeysuckles (Lonicera spp.) and California pipevine (Aristolochia californica) for flowering vines for a shady area. California honeysuckles are not aggressive and like to grow into and through other bushes. There are species adapted to both moist and dry areas and different shades of flowers. Without support, California honeysuckle acts like a groundcover. Pipevine is deciduous and fairly drought tolerant (but can also tolerate moist soils). It has very unusual flowers that are about 1 inch long and shaped like a small pipe. Larva of pipevine swallowtail butterflies live on this vine.
Before you decide to plant any of these plants in your garden, review the growing requirements to make sure they're a good fit for what you have in mind. With a little research, you will find many other options as well.
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by Penny Pawl, U.C. Master Gardener of Napa County
I recently discovered bunchberry (Cornus canadensis) and could not resist.I admit I am a plant collector but that is another story. The bunchberry is a ground-hugging member of the dogwood family.The leaves resemble the leaves on bigger dogwoods but are much smaller. It only grows about eight inches high but has the same showy white blossoms
When I looked for information on this little guy, I discovered that the dogwood family is quite large. Dogwoods are found within the temperate zones of the Northern Hemisphere. Some are native to the West Coast. The bunchberry also is found in Greenland.
The bunchberry thrives in moist, shady areas, so if you decide to plant one, know that it has specific needs. Plant it in an area that stays cool and shady. Instead of a tap root it has many fibrous roots that grow from a rhizome or mass of roots, which can send up new plants.
The bushberry's small blooms produce edible berries in the fall. I transplanted mine to a larger pot and it has since almost filled the pot. Some of the outside branches are now creeping across nearby soil.
Dogwoods like to grow under the shade of other trees. I recall driving through Virginia in April years ago and seeing the beautiful blooms floating in the shade of the overhead trees. The Western dogwood is native to the redwood forests near Mendocino. Most give a beautiful display in May.
The ones most popular in Napa County gardens are the Eastern dogwood (Cornus florida), Western dogwood (Cornus nuttallii) and red twig dogwood (Cornus alba ‘Elegantissima'). I especially love a small bush variety that was given to me many years ago by a nurseryman. I have taken many cuttings off the plant, but I have not been able to identify it. It grows about three feet tall and every spring puts out many blooms that look like a spray of stars.
Another dogwood growing in my garden is Cornelian cherry (Cornus mas), also known as European cornel or Cornelian cherry dogwood. I kept expecting the big white flowers on this tree but what finally appeared were small yellow flowers. None of these flowers have ever turned into fruit although I have read that it does produce small red berries. This tree grows vigorously and takes well to an annual severe pruning which I often do during the summer months.
Dogwoods do not do well in either flooding areas or dry soils. They like fertile soil and will slowly die if not given the right conditions. Root rot from excess soil moisture is one of the most frequent causes of death. If soil does not drain properly, the roots rot and little can be done to correct this situation.
Diseases that bother dogwoods include anthracnose and crown canker disease. Both are fungal diseases. Avoid damaging the tree trunk as that is often how diseases enter the tree. Some borers also attack dogwoods. However, in all the years I have had dogwoods in my garden, the worst threat I have encountered is some scale on the newer growth. I scrape those off with my fingernail rather than try to remove with chemicals.
In warmer climates, the bark can sunburn, which may cause the tree to decline and die. This bark damage may also invite borers, which can kill the tree. If you find borers in branches or limbs, cut them off below the infestation and dispose of the wood. If the borers are in the main trunk, the tree may be a total loss. Some dogwood hybrids are resistant to some of these diseases and pests, but they can only be reproduced by grafting and cuttings, not by seed.
In the fall, dogwoods produce a blaze of red leaves ranging from pink to burgundy-orange to blood-red.
UC IPM Pest Note on Anthracnose updated May 2020:
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7420.html
Crown canker of dogwood:
http://plantclinic.cornell.edu/factsheets/dogwoodcrowncanker.pdf
The UC Master Gardeners of Napa County are volunteers who provide University of California research-based information on home gardening. To find out more about home gardening or upcoming programs, visit the Master Gardener website (napamg.ucanr.edu). Our office is temporarily closed but we are answering questions remotely and by email. Send your gardening questions to mastergardeners@countyofnapa.org or leave a phone message at 707-253-4143 and a Master Gardener will respond shortly.
By Corinne Yoshihara, UC Master Gardener of Napa County
As I traveled through Napa Valley this spring, I made a special effort to note the progression of colors on trees lining my route. Color change (or the appearance of color) occurs every year, yet I never tire of it. It's one of my favorite aspects of spring and it's especially noticeable on trees. I enjoy watching the transformation of stark brown branches to those with pops of whites, pinks and, now, green.
Having had a good winter rain, the flowers were particularly abundant this year (as are the weeds, sigh). I first noticed the white flowers of evergreenpear trees in February. Their white flowers were striking against the grey sky, made even more pronounced by the scarcity of other flowers. Pollen-covered anthers lent a charming speckled appearance to the white petals.
With the landscape being so bare, it was also easy to spot the large white flowers flushed with purple of the saucer magnolia, one of the early blooming hybrids of magnolia. The creamy white flowers of southern magnolia didn't make their appearance until May.
When the February rains took us into March, I noticed more arboreal change. Plum trees were covered with soft pink or white blossoms. Bare maple trees sported flowers resembling little red or yellow-green (red maple and silver maple, respectively) balls of bristles. Also around this time, bright pink pea-like flowers covered the branches and trunk of the redbud tree displaying a trait called cauliflory, or “flowering on mature trunk.”
By April, many more trees were in bloom. I saw striking red clusters of the red horse chestnut flowers, white fringe-tree flowers that resembled dragonfly wings, and crabapple blossoms in colors of white, pink and red.
One tree in particular was especially beautiful in April, the dogwood, one of my favorites. Usually blooming under the dappled light of shade trees just beginning to leaf out, the dogwood's tiered branches are sheathed in white, pink or red depending on the variety. The “flowers” are actually four bracts or modified leaves and the actual flowers are tiny, forming a rounded yellowish cluster in the center of the bracts.
Leaves were out on many trees by May, late spring. It seems like they slowly peep out of their bud covers and then, while you're distracted, cover the entire tree in fresh, unmarred chartreuse. Still, I was able to pick out the flowers of tulip, cherry and hawthorn trees.
The opening of buds raises a lot of questions for the biologist-at-heart. Here is one of mine. Did you notice that many of the earlier flowering trees had no leaves? This behavior of flowering before leafing is called hysteranthous. Although both flowers and leaves begin as buds, flower bud opening is not tied to leaf bud opening.
There are even differences in the times of flowering and leaf unfolding between tree species. Pear, plum, redbud, dogwood, magnolia and cherry trees, for example, all flower prior to leafing. On the other hand, crabapple, horse chestnut and tulip trees have both leaves and flowers at the same time.
Moreover, leaf and flower bud openings can vary within a genus. For example, for the maple genus (Acer), bigleaf maple flower buds open at the same time as its leaf buds; silver maple flower buds open when its leaf buds are still tightly closed; and sugar maple leaf buds open but not its flower buds.
Since flower and leaf bud opening behaviors are not tied, the mechanisms that control them must be distinct. In addition to climatic (chilling, light, heat) requirements, there is a genetic component to flowering. It gets complicated!
Whatever the mechanism may be, it appears that time of flower or leaf opening confers advantages to trees. Trees that produce flowers first, place all of their stored energy into the important process of reproduction before other trees have a chance to leaf out and grow. Also, since flower production, like leaf production, requires sunlight, early flowering ensures that leaves don't block sunlight, or interfere with wind pollination. Masses of flowers may also attract more insect pollinators.
Next time you're outdoors admiring nature's beauty, pay attention to the little things happening around you. You may come up with your own questions. Bring them to the Master Gardeners Tree Walks and share them with us.
The UC Master Gardeners are volunteers who provide UC research-based information on home gardening and answer your questions. To find out more about upcoming programs or to ask a garden question, visit the Master Gardener website (http://napamg.ucanr.edu) or call (707) 253-4221 between 9 a.m. and noon on Mondays, Wednesdays or Fridays.
