by Penny Pawl, UC Master Gardener of Napa County
Napa County Master Gardeners invite a guest speaker to every monthly meeting, part of the MGs' continuing education requirement. Recently, the guest speaker was Pam Bone, who brought great knowledge and excitement to the subject of trees, her area of expertise.
Bone helped start the Master Gardener program in Sacramento 40 years ago and became the first California Master Gardener program coordinator. She has retired from UC Cooperative Extension but still volunteers at the help desk in the Master Gardeners' Sacramento office, gives talks and consults on landscape problems. She has a degree in plant science from U.C. Davis. She also provides tree advice to landscapers and others in the Sacramento area.
Speaking via Zoom to the UC Master Gardeners of Napa County, she addressed some of the many myths surrounding trees in our landscape. Topics she covered included trees planted in a lawn, staking young trees, root problems, topping trees, fertilizer and planting the right tree in the right place.
The myth about purchasing the largest tree you can afford: At the nursery, many people choose a large tree over a younger, smaller one of the same type. But the smaller one will likely do better when planted. Often large trees have leaf mass that is much larger than the root mass, and the roots cannot supply enough water to the canopy. The treetop suffers and the tree dies from lack of water. Bone showed us examples of plantings where every tree had died.
The myth about tree roots:When trees grow in a container, the roots are often overgrown. The trapped roots circle around themselves and are unable to spread out to anchor the tree properly when it's planted.
Although young trees may have a tap root, it is generally not long lived. Other roots, known as feeder roots, will grow, reaching out beyond the canopy to search for water and nutrients in the soil. I have seen this phenomenon in my own garden; redwood feeder roots are everywhere. According to Bone, 90 percent of a tree's roots are in the top 18 inches of soil. Ninety-nine percent of a tree's roots plunge no deeper than three feet.
The myth about fertilizing: Do not fertilize a sick tree, said Bone. Healthy soil has the elements a tree needs to thrive as long as the tree's other needs, such as sunlight and water, are met. Storebought fertilizer does nothing to help trees or many other woody shrubs grow. Instead, apply aged compost over the root zone, keeping the compost 12 to 15 inches away from the trunk. Compost keeps the soil cool, controls erosion and conserves water. And as it breaks down, it feeds the soil microbes.
The myth about planting trees in lawn: Trees and lawns have different water needs. Keep an area around the tree free of lawn and water the tree deeply but less often than the lawn. I had a large tree planted near my lawn, and although I watered the lawn constantly, it looked awful. When I finally let the lawn die, the tree died, too. I discovered that the entire lawn was undermined by the tree's feeder roots.
If you do have a tree planted in lawn that you have stopped watering, you still need to water the tree. Water deeply about once a month to keep it alive until we get rain.
The myth about staking newly planted trees: If you purchase a tree from a nursery, it will probably be staked. Remove this stake when you plant. The tree needs the ability to move with the wind; staking too tightly weakens the tree by restricting this movement. Just as humans build muscles through exercise, trees build strength through movement. Bone demonstrated how to properly stake a tree with two stakes and correct placement of supports.
The myth about using wound paste: Bone said that there was no need to use sealers or tree-healing products on pruning cuts. A deep wound or a cut that's too close to the trunk cannot be corrected with a sealer. Correct cuts will heal naturally.
Bone also advised against topping trees. Trees are meant to grow to a certain height; topping them can compromise their health. It reduces the leaves available to make food, weakens new branches and exposes the tree to disease and pests by allowing strong sunlight to enter the main parts of the tree and possibly cause sun scald.
Bone reminded us not to water our oak trees in summer. Compost and leaf litter should be left around the root zone but kept away from the trunk to prevent rot.
The UC Master Gardener website also has many resources to help you with tree care, planting and pruning.
Napa Library Talk: Napa County Master Gardeners will give a talk on “California Native Bees and Creating Bee Habitat” on Thursday, September 2, from 7 p.m. to 8 p.m. via Zoom. Learn how to attract bees of all kinds to your garden. Register here to receive the Zoom link.
Food Growing Forum: Napa CountyMaster Gardeners will present a discussion of “Culinary Herbs” on Sunday, September 12, from 3 p.m. to 4 p.m., via Zoom. Register here to receive the Zoom link.
Free Guided Tree Walk: Join Master Gardeners of Napa County for a tree walk in Fuller Park in Napa on Tuesday, September 14, from 10 a.m. to noon. Limited to 12 people per walk. COVID safety protocols will be followed. You will be asked health questions and asked to sign in. Face masks and social distancing are required. Register here.
Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to mastergardeners@countyofnapa.org or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email.
For more information visit http://napamg.ucanr.edu or find us on Facebook or Instagram, UC Master Gardeners of Napa County.
By Susanne von Rosenberg, UC Master Gardener of Napa County
Gardening myths can come from many sources. A fair number arise when information applicable to agriculture is misapplied to home gardens. Others are based on what seems like a logical extension of science.
Let's take the myth of disinfecting or sealing pruning cuts. You can still easily find wound-sealing compound in garden-supply centers and online. At first glance, it seems like a really good idea to disinfect or cover an open pruning wound. After all, we know that disinfecting and covering our own wounds to keep out germs and dirt leads to better healing.
However, in the vast majority of cases, trees and other woody perennials heal better if the wound is left untreated. They form a natural callus that repels pathogens. Disinfecting the cut damages the tissue further, and studies show it leads to greater loss of tissue than not disinfecting. Sealing the cut seals in moisture and pathogens and prevents the callus from forming.
Another logical-sounding myth is that mulching with wood chips from tree trimmings could spread disease because the chipped trees may have been diseased. A related myth is that the chips might inhibit plant growth if they came from trees that exude allelopathic chemicals, compounds that inhibit other plants.
Wood chips should only be used around perennials. They are not suitable as mulch for annual plants or vegetable gardens. In my research I was only able identify one relatively common local tree, black walnut, that might present a problem when used as wood chip mulch.
Many trees contain allelopathic compounds, but in mulch, this is actually a benefit. The chemicals are unlikely to affect established plants, but they will reduce weed-seed germination and weed growth.
Wood chip mulches may create a nitrogen deficit where the mulch meets the soil, but that also helps reduce weed growth.
There is no evidence that pathogens in wood mulch can transmit disease to established plants if you keep the mulch three inches away from the trunk or base of the plant. Applying four to six inches of wood chip mulch to your garden is an inexpensive, sustainable practice. In highly disturbed or eroding soil areas, or when working to control perennial weeds, eight to twelve inches is recommended.
Another common gardening myth that sounds logical is that you should amend the soil in a planting hole. Some sources recommend adding 25 to 50 percent organic matter or other amendments. It makes sense that improving the soil and adding nutrients would improve the growth and survival of the plant.
Initially, this may be true. But by radically changing the soil in the planting hole compared to the native soil, you are effectively creating a “pot” in the ground. When the roots encounter the harder, finer native soil, they will circle back to the material in the planting hole. With access to only the water and nutrients in the planting hole, the roots won't be able to support the canopy. Also, the planting hole will act as a reservoir for rain, depriving roots of oxygen. In the dry season, irrigation water will leach out of the planting hole into the native soil and become unavailable to the roots. Finally, most of that organic matter will eventually decompose and your plant will sink.
Sometimes a gardening myth is only partly untrue. Advice may be valid for certain climates or soil types but not for other locations. That why it's important to make sure that recommendation are appropriate for our climate.
Before I became a Master Gardener I was fascinated by the idea of “sunken beds,” a gardening technique for conserving water in dry climates. The idea seemed applicable to my area but it wasn't. Sunken beds were developed for the arid southwest. By planting seedlings in an area excavated six inches or more below ground level, they are more protected against wind, and the surrounding soil provides some cooling. In addition, the beds can capture and retain water from monsoon rains.
But the Napa Valley rainfall pattern is different. Compared to the arid Southwest we get a lot of winter rain. Unless your soil has good percolation, your plants will drown in sunken beds, and your soil will be oxygen deprived.
Successful gardeners are always learning and thinking critically. When you hear or see gardening advice, make sure that it has a basis in science and is applicable to our climate.
Napa Library Talks: First Thursday of each month. Register to get Zoom link. http://ucanr.edu/wildlifehabitat2020
Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to mastergardeners@countyofnapa.org or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email.
For more information visit http://napamg.ucanr.edu or find us on Facebook or Instagram, UC Master Gardeners of Napa County.