By Susanne von Rosenberg, UC Master Gardener of Napa County

Some gardening advice seems so sensible or obvious, or has been repeated so often, that we “know” it to be true. As gardeners, we need to be careful about falling prey to myths. In this column, we'll explore some widespread gardening myths, although perhaps I should call them confusions.

We are usually told that wilting leaves indicate that a plant needs water. This is often the case, and you can check to see if your soil is dry. But there are other reasons that a plant's leaves could be wilting.

If the soil is waterlogged, the oxygen that roots need to grow is replaced with water. This happens often to plants in containers without drainage. Plants may also become waterlogged in compacted soil that doesn't drain well. When roots lack oxygen, they can't supply water to the rest of the plant. The leaves continue to photosynthesize and to use water. By forcing roots to shut down, waterlogged soil leads to wilted leaves.

Fungal or bacterial disease can also cause leaf wilt. Fusarium and verticillium are common in local soil. These fungi block the plant's water transport structures, causing leaves to wilt even when there is plenty of soil moisture. Often the entire plant dies.

Keeping your soil too moist can promote fungal disease. Another culprit for wilting leaves is animal damage to the roots. Gophers, nematodes and other insects feed directly on roots, and other animals may create tunnels that drastically reduce root contact with surrounding soils.

Another possible cause of wilting is overfertilizing or excess salt in the soil. Always follow the directions on any packaged fertilizer, and be aware that steer manure is relatively high in salt.

You may have heard that bark chips are a better mulch for your perennial woody plants than tree chips. Some say that tree chips could contain disease-causing organisms or compounds that inhibit the growth of other trees.

Neither of these concerns has been documented as a significant issue. Conversely, bark chips, while a more attractive mulch than tree chips, have poor water retention. Tree bark is designed to prevent water loss. It contains a waxy compound, suberin, that repels water.

Tree chips, on the other hand, consist mostly of inner wood, which has the capacity to absorb and hold moisture. Depending on where the logs were stored before the bark was collected and chipped, bark chips can also contain weed seeds. Tree chips are more environmentally friendly, too, because they are local. By using them, you are reducing the amount of material that needs to be processed in a composting facility.

While we're talking about mulch, let's explode the myth that there is any permanent solution for weed control other than paving over your yard. Landscape fabric, which differs from black plastic mulch in having small holes for air and water exchange, is often touted as a permanent solution. It is used in commercial vegetable and ornamental plant production, where it is successful at keeping weeds out. It can also be easily removed and replaced each year.

However, landscape fabric is not good for permanent weed control around perennials. If left exposed, the fabric can degrade in a year. If you cover it with mulch or allow plant debris to accumulate on top of it, weeds will colonize the plant material or mulch and grow through the fabric, making it difficult to remove.

You can cover the fabric with gravel, but you'll still need to keep removing the weeds that manage to colonize gravel-covered fabric. Your plants may also grow into the fabric, so when you remove the fabric, you damage their roots.

As the fabric degrades, you'll have a clean-up and aesthetic headache, with lots of shredded bits. (I know this from personal experience.) Gophers can exert so much pressure building mounds under the fabric that the fabric rips. If it doesn't rip, you end up with exposed landscape-fabric-covered mounds.

Unfortunately, there is no magic bullet for weed control. You can reduce them, but you still need to remain vigilant no matter what method you use. Organic mulches are best as they improve soil texture and health and can be replenished as needed. Couple them with targeted watering.

If you want to learn more about garden myths, Dr. Linda Chalker-Scott, an extension horticulturist and associate professor at Washington State University, has a wonderful website that discusses all sorts of common Horticultural Myths.

Food Growing Forum: Napa CountyMaster Gardeners will present a discussion of “Perennial Vegetables, Garlic and Alliums” on Sunday, October 10, 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, October 12, 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

It's been impossible not to notice how different our fall season is from what we were used to in the past. Rains come four to six weeks later, if they come at all. We get heat spells into October and sometimes November, and big fires are burning somewhere.

Napa County Master Gardeners have been providing workshops and other information on fall vegetable gardens for more than 10 years. Fall vegetable gardening used to feel almost like a freebie: just water the plants long enough to get them well established, and by early to mid-October nature would begin to water them for you. Even if you had to water periodically, the plants needed less water because of the predictably cooler and more humid weather.

Recently, I've had questions about whether fall vegetable gardening still makes sense, and how to deal with the changes. Yes, it still pays to put in a fall vegetable garden, but we need to consider the changes in rainfall patterns and autumn temperatures.

The best things you can do to make your garden more resilient are to improve the health of your soil and to mulch your garden. Healthier soil holds more water, and it also provides better conditions for plant growth. A plant in healthy soil will be able to handle more stress than a plant in more marginal soil. Mulching helps conserve water, reduces weeds (which compete for the available water) and adds organic matter to the soil if you use a mulch composed of organic material.

Given the changes in rainfall patterns, be prepared to water your fall vegetable garden. Plants will need less water than in late spring or summer because autumn temperatures are lower and days are shorter. But don't do what I've done (more than once) and keep waiting for the rain that never comes. I've lost or stunted several crops because I kept expecting it to rain “any day now.”

These days I water using the same basic principle as I do in the summer. When the soil in a vegetable bed is dry 1 to 2 inches down, it's time to water, even if it is December. Seeds and young seedlings need more frequent watering.

The more challenging question these days is “When should I plant?” We used to say that, in most areas in Napa County, you could plant seedlings for fall crops such as broccoli and cauliflower by mid-August for a harvest around the end of October. Planting as late as mid-September would give you a crop by late November. Planting after the middle of September would most likely mean that your “fall” crop would mature in the spring.

I no longer plant in mid-August. The risk that my plantings will fail due to heat is just too high. Even if I can keep the seedlings alive with shade and a lot of water, they will be stressed and therefore less productive and more susceptible to disease and insect pests.

I now plant no sooner than the beginning of September, and more typically toward the middle of September. Planting later in the fall means that my first harvest is delayed. I can partially make up for this by planting some vegetables that mature more quickly than broccoli and cauliflower, such as Asian greens and lettuces.

I also grow some vegetables in containers that I used to start in the ground. I can grow them in the coolest areas of my garden, even bringing them inside during the hottest part of the day. Peas work well when grown this way.

Also, for fall planting, it's a good idea to choose the varieties with the shortest days to maturity. Broccoli harvest can vary from 55 days to more than 90 days from transplanting. Choosing bolt-resistant vegetable varieties is another important tactic for fall planting.

Although planting later in the season delays the harvest, warmer temperatures mean that plants grow later than they have in the past. Plants need light to photosynthesize, and the shorter days and lower light intensity in the fall reduce the rate of photosynthesis. However, photosynthesis also requires a certain minimum temperature; depending on the plants, photosynthesis virtually stops at temperatures below 38°F to 50°F. For most plants, the rate of photosynthesis is highest between 50°F and 68°F. (Also worth knowing: Photosynthesis nearly stops at temperatures above 104°F.) The higher fall temperatures that we have been experiencing won't compensate for the reduced sun intensity, but they do help us get a slightly longer fall growing season.

Food Growing Forum: Napa CountyMaster Gardeners will present a discussion of “Perennial Vegetables, Garlic and Alliums” on Sunday, October 10, 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, October 12, 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

Recently, someone asked me about the best trees to plant to help reduce climate change. Planting any tree is helpful, because all trees pull carbon dioxide out of the atmosphere and store the carbon in the form of wood. Trees also provide shade that reduces your energy needs. Areas of cities with plenty of trees can be up to 9°F cooler than similar areas lacking trees. Shaded surfaces may be 20°F to 45°F cooler than unshaded materials.

When choosing a tree with climate change in mind, there are several factors to consider. Long-lived trees are preferable because the carbon stays locked up longer. (Some carbon is released when a tree decays.) Fast-growing trees store carbon more quickly than slow-growing trees. Given that our climate is changing, it also makes sense to plant trees adapted to warmer climates.

Evergreen trees photosynthesize longer each year than deciduous trees and continue to remove carbon from the atmosphere when deciduous trees are dormant. In Northern California we must also consider a tree's water needs and fire resistance.

Finding a tree that meets all those criteria seems like a tall order, but we do have several attractive choices. Suitable large trees include coast live oak, valley oak, California sycamore, white mulberry and American red maple. All these trees grow more than 2 feet per year once established. Coast live oaks reach 20 to 80 feet in height and valley oaks reach 40 to 70 feet. Both make great shade trees. Coast live oaks are also shade tolerant.

Once established, these oaks can get by with as little as 12 inches of rain per year and can live for 150 years or more. Oaks are on the list of Napa County fire-wise plants.

Sycamores are also known as plane trees. California sycamores are native to the state and grow in a wide variety of habitats. They reach heights of 30 to 100 feet and have a spread of 20 to 70 feet. Once established, California sycamores manage with as little as 11 inches of rain per year.

These trees are known to have aggressive roots, so plant at least 12 feet from structures and sidewalks. California sycamores are long lived, with some specimens known to be more than 400 years old. Like the oaks, California sycamore are on the list of Napa County fire-wise plants.

White mulberries are not native, but they are drought tolerant, requiring as a little as 10 inches of rain per year once established. They grow up to 40 feet tall, and the canopy is approximately as wide as it is tall. Some cultivated varieties have a weeping form. The fruit can stain sidewalks, so you may want to consider a non-fruiting variety. They have a relatively short lifespan, typically 25 to 50 years.

American red maple is also not native to California. However, this tree can grow in almost any soil type and is very drought tolerant. American red maples grow about 3 feet each year, up to a height of 60 to 90 feet with a spread of 25 to 45 feet. They typically live 80 to 100 years. Maples are on the list of Napa County fire-wise plants. American red maple is used for maple syrup, although sugar maples are more commonly used.

You may wonder why I haven't mentioned coast redwoods. They are certainly long lived, fire resistant and relatively fast-growing, and they can store an impressive amount of carbon. However, they require at least 22 inches of rain per year, which means that in many areas of Napa County they will need supplemental water in dry years. You may have noticed that many redwood trees have dead and dying branches, the result of our recent dry years.

If you are interested in raising your own trees from seed, the National Reforestation, Nurseries and Genetics Resource Program has a guide that provides a good overview. It is best to use seed collected locally, as trees adapt to local conditions. Acorns from a Sacramento valley oak would probably not do as well in Napa County as acorns collected here.

Whatever tree you choose, plant it correctly to give it a good start. A seedling or young tree with a three-foot weed-free zone around the trunk may grow twice as fast in the early years as the same tree surrounded by weeds or lawn. Contact the Napa County Master Gardeners for a helpful guide to planting landscape trees.

Food Growing Forum: Napa County Master 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.

Napa Library Talk: Napa County Master Gardeners will give a talk on “Replace Grass, Save Water and Get Cash” on Thursday, October 7, from 7 p.m. to 8 p.m. via Zoom. Learn how to replace your thirsty lawn without digging it up. Register here to receive the Zoom link.

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

Can you believe it's already September and we're headed into fall gardening season? It's time to assess what you would like to grow this autumn.

Now is the right time to plant cool-season vegetables, fall annual flowers and—as soon as the rains start—California native plants It's also the moment to plant spring-flowering bulbs.

I love bulbs because they are so easy to care for and add such beauty and joy to my garden. Bulbs to plant now include daffodils, crocus, many types of lilies, bearded iris and tulips. Plant freesia, canna, begonias, gladiolus, crocosmia and dahlias in late winter and early spring for summer bloom.

There are five major types of plants that we refer to as bulbs: true bulbs, corms, tubers, rhizomes and tuberous roots. Bulbs store food (in the form of carbohydrates) to support growth and flowering for the next growth cycle. Most are perennials, although some, such as hyacinths, can be short-lived. Bulbs initially produce leaves, followed by flowers. Bulbs need only a light application of fertilizer after the leaves emerge.

After flowering and the growing season end, bulbs typically go dormant and the plant dies down to the ground. For bulbs that flower in spring, the growing season lasts until late spring or early summer.To ensure that your bulbs continue flowering year after year, keep the leaves until they naturally die back or turn yellow. You can cut back dead flower stalks at the base at any time. After the plant flowers, its leaves continue to produce carbohydrates to store in the bulb.

Water as needed to keep the leaves alive for the rest of their growing season. (Too much water may cause the bulbs to mildew or rot.) After you remove the leaves, you can dig up the bulbs and store them in a cool, dark, dry place, or you can leave them in the ground. Some bulbs need to be divided regularly to keep flowering well. If you leave bulbs in the ground and they are not performing well, consider digging them up and dividing them.

Daffodils, tulips, lilies, amaryllis and hyacinths are all true bulbs. True bulbs are composed of a series of leaves modified for food storage. Onions and garlic are also bulbs; when you cut through an onion, the rings you see are the leaves. Garlic and lilies form a looser bulb. All true bulbs root from the bottom. If you're not quite sure which side is the bottom, plant the bulb sideways.

Corms are another common type of bulb. Instead of modified leaves, corms are modified stems. The bottom of a corm is actually the base of a stem. Corms are easy to confuse with true bulbs because they look a lot like them. To know whether you're looking at a true bulb or a corm, cut the bulb in half to view its internal structure. If it's solid, it's a corm. If you see rings, it's a true bulb.

Freesias, crocus, gladiolas, watsonia and my favorite, crocosmia, are corms, as are water chestnuts. Some corms, like freesias and watsonia, have a kind of furry covering. Buds are located on the tops of the corm, and roots and baby corms (cormels) grow from the bottom.

Tubers are also underground stems. They differ from corms in that they are not the base of the stem. Common flowering tubers include anemones, begonia and cyclamen. Tubers have nodes (on potatoes, we call them eyes) that can appear anywhere on the tuber and sprout both new shoots and new roots. Other tubers you might be familiar with include yams, turmeric and ginger. Tubers can grow in any direction.

Rhizomes are elongated bulbs that are a type of underground stem. Unlike tubers, they only grow horizontally. Calla lilies, cannas and bearded iris are examples of rhizomes. (Dutch iris is a true bulb.) Leaves and buds grow only from the top of a rhizome, and roots grow only from the bottom. Rhizomes can sometimes emerge above the surface of the soil, and rhizomatous bulbs should generally be planted shallowly.

The last major type of bulb is a tuberous root. Tuberous bulbs are thickened roots that radiate from a central stem. Agapanthus, society garlic, dahlias and day lilies have tuberous roots. The growth buds are at the base of old stems, not on the tuberous roots. 

Different bulbs require different planting depths. Plant bearded iris just below the soil surface; plant tulips deeply, up to eight inches deep in loose soil. For recommended planting depth, consult your bulb source or a reputable online source. The Sacramento Master Gardener website has a great bulb-planting schedule that also provides information on planting depth and spacing.

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.

Napa Library Talk: Napa County Master Gardeners will give a talk on “Replace Grass, Save Water and Get Cash” on Thursday, October 7, from 7 p.m. to 8 p.m. via Zoom. Learn how to replace your thirsty lawn without digging it up. Register here to receive the Zoom link.

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.