by Denise Levine, U. C. Master Gardener

Now is a good time to plant onions in Napa Valley. Walla Walla, Red Torpedo and Red Burger are just some of the seedling varieties I have seen in local nurseries, and a variety of seeds and “sets” (small bulbs) for onion relatives—such as chives, pickling onions and scallions—is available, too.

Onions are members of the Amaryllis family. Instead of a flamboyant flower, they have strappy edible leaves and edible bulbs that store energy and moisture to help the plant survive summer. Allium cepa is the species we grow as onions, and it has been cultivated and eaten for centuries all over the globe.

Young onions need cool temperatures to thrive. They grow to pencil size through the fall and winter, then develop bulbs as the days grow longer again in the spring.

Onions need soil amended with organic matter with low sulfur content, as sulfur is thought to contribute to pungency. Manures and compost are good sources of organic amendments that rain won’t leach.

You can plant large storage onions now, use the thinnings over the winter as scallions, and then harvest large bulbs in the spring or summer for storing. Many other smaller varieties can be started now and over the next few months, for harvest through the winter, spring and summer.

University of California experts recommend growing onions in raised beds, preferably in sandy soil and with drip irrigation. But amended beds in the ground are also fine, and many scallion varieties are successful in large pots.

To grow large onions, the University recommends planting onion transplants or sets three to four inches apart, in rows one to two feet apart. Other sources recommend three to four inches all around, then thinning and weeding onions to provide room as they grow. This method requires frequent light feedings.

After the Napa County Master Gardener onion trials last year, we agreed that drip irrigation not only conserved water but also minimized weeds. Overhead watering encouraged weeds, direct competition for the nutrients your onions need.

Onion seedlings look like miniature green onions. To harvest big bulbs, plant seedlings  three to four inches apart. They need full sun and frequent light watering for the 12- to 18-inch root zone. They also appreciate a light monthly feeding of fish emulsion or other fertilizer.

About 130 to 150 days after transplanting, your large onions will start to yellow. Stop watering to prevent the bulbs from splitting. After at least two weeks, and after the leaves have fallen over and begun to dry, carefully dig your onions and brush off the dirt. Don’t get them wet! Cure them in a dry, shady spot until the tops are brittle before storing in a cool. dry place. In Napa, onions tend to have a short storage life.

Onion “sets,” which look like miniature bulb onions, can also be planted now. The same spacing and requirements appl

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By Yvonne Rasmussen, U. C. Master Gardener

This time of year, as the weather starts to cool and we get a little more moisture in the air, we start to see some fungi in the garden. These might be mushrooms growing in the lawn or at the base of a tree, or conks growing out from the trunk. Other smaller fungi can produce white, black or orange spots, fuzzy material or residue on leaves. Still others make strange forms we might not recognize as fungi, such as puff balls, earth stars, galls or masses on branches or soil.

Some of these peculiar protuberances are caused by the closely related slime molds, such as the so-called “dog vomit” slime mold seen in the spring. This mold produces a bright yellow, frothy-looking growth on soil, often near the base of trees or other plants.

Fungi play an important role in the environment. They help decompose plant material that cannot easily break down otherwise.

But they can also cause plant diseases and problems in the garden. Fungi generally need moisture for reproducing, which they do by means of spores. Generally spread by wind or water, spores are a little like tiny seeds. The powdery substance you feel on the underside of a rose leaf  infected with rust is the rust spores. You can sometimes see spores on the underside of a mushroom, or in the smoky substance from a puffball.

Althought some fungi are edible, others are deadly poisonous and some are major allergens.

In the fall, powdery mildew often develops on the leaves of vegetables and ornamentals. It may look like white spots or a dusty coating on the leaves. Leaves infected with powdery mildew will eventually turn yellow, die and fall off.

Powdery mildew prefers cool, moist places. It does not do well in full sun and heat, so it appears first on plants in shady areas.

To avoid powdery mildew, plant in sunny locations and provide good air circulation. Keep plants pruned properly to encourage air circulation and don’t over fertilize. Too much fertilizer promotes fast, weak, leafy growth that will need more water. Excess nitrogen in the soil—what the plants can’t use—washed into our waterways and promotes algae growth.

For many vegetable crops and deciduous plants, there’s no good reason to treat for powdery mildew since the plants will soon be removed or go dormant. Most treatments can prevent the fungus, but they don’t cure it. This means you need to treat before you see symptoms.

Treatments need to thoroughly cover all susceptible plant parts. Mild to moderate symptoms can be treated with horticultural oils or plant-based oils. Follow package directions carefully. These oils can damage plants if used within two weeks of a sulfur application, or when temperatures are high, or if plants are drought stressed.

University of  California Cooperative Extension has three free “Pest Note” publications related to controlling powdery mildew. You can read the

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By Sue Hurley, U. C. Master Gardener

The first time I gazed upon a dahlia I was with my father, driving up the Arlington Circle in Berkeley. I spotted a driveway filled with black pots and tall plants that had dinner-plate size flowers.  I had never seen anything like them.

Dahlias are a perennial that grows from tuberous roots and blooms from mid- to late summer until first frost. I must warn you now: Collecting them can be addicting.

I love them because they make wonderful cut flowers and last a  long time. The best dahlias for cutting are those with multi-petaled medium to small flowers. Large dahlia blossoms can be floated in a bowl.

Dahlia blossoms range in size from two inches in diameter to dinner plate size. They come in 15 hues and may be a solid color, bicolored or multicolored. There are 19 different shapes, including single, cactus, ball, informal and formal decorative, and pompon types. Dahlias range in height from 12-inch dwarfs to 8-foot giants.

Wait until after the last spring frost to plant them. The soil should be warm enough by mid May. Dahlias love full sun and do well in our Mediterranean climate; they will tolerate light afternoon shade in very hot areas.

Dig a hole one-foot square. Work some peat moss or steer manure into the soil. I also work a small handful of bone meal into the bottom of the hole. Plant the tuber horizontally four to six inches deep.

Drive a stake of appropriate size into the ground now so that you don’t damage the roots later on. Dahlia tubers have small “eyes,” which are the growing points of the plant. Place the stake a couple of inches from the eye so you can easily tie the stems to the stake for support.

Now cover the tuber with soil and water well. Snails love the new sprouts so scatter some snail bait. After they sprout, dahlias will need deep watering two to three times a week, and more often in  warm weather.

Dahlias like low-nitrogen fertilizers such as those used for vegetables. Give them the first feeding a month after planting, and another feeding three to four weeks later. High-nitrogen fertilizer can produce small blooms, no blooms or weak stems, and cause the tubers to rot or shrivel during winter storage.

In the fall, dig up your dahlias two weeks after a killing frost. They will be brown then. If you dig too early, the tubers will not store well. Cut the foliage to about four inches and lift the plant out with a spading fork. Wash the dirt off and let them dry overnight in a protected area. Tubers should be stored for winter in cardboard boxes.  Layer with sawdust or peat moss using newspapers to separate layers, and store in your garage.  Write the name, color, and size on each tuber with a black marker.

In spring, a few weeks before planting time, you can divide the tubers by cutting the stalks with a sharp knife. Leave one inch of stalk for each tuber, which in turn needs at le

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By Bill Silfvast, U. C. Master Gardener

Do you have cute little animals in your backyard that you enjoy watching as they chase each other around the tree branches and hop along the fence, occasionally sitting up to look around at their beautiful environment? You might even get the urge to cuddle them since they appear so lovable.

Or do you have awful little pests that eat your homegrown fruit, including figs, grapes, walnuts, persimmons, kiwi, cucumbers and tomatoes? Do they dig holes in the ground to store nuts, eat all of your bird seed, make messes on your patio, eat through the roof of your garden shed to gain access to some bird seed, or generally just make nuisances of themselves?

Both descriptions apply to the same creature: the squirrel.

Although we don’t like to think of them as such, squirrels are members of the rodent family. Perhaps it’s the fluffy, bushy tail that allows us to distinguish them in our minds from rats and mice. The word squirrel comes from the Greek word for shadow tailed, because squirrels use their tails to shade their bodies.

Squirrels cannot digest plant cellulose, so their diet consists mainly of foods high in protein, carbohydrate and fat. Nuts are an ideal food for them. But once their buried nuts begin to sprout in the spring and are no longer tasty, these creatures have a difficult time finding food. They will then resort to eating the buds of trees and plants.

As you may have noticed in your own garden, squirrels typically consume a wide variety of foods, including nuts, seeds, fruits, fungi and some types of green vegetation. They have also been known to eat insects, small birds, young snakes and smaller rodents if they get hungry enough.

Their cleverness is readily apparent. They dig holes in planting pots to reach the bulbs they love to chew on. They steal the seed out of bird feeders. They bury food in the ground, or find crevices in roof eaves to store food. Their sharp teeth provide access to many places that we might normally consider “squirrel proof.” They will even chew on the insulation of wiring as a food source.

Carefully sealing your shed, garage or house will usually keep them out, but check regularly for chewing marks if you have a squirrel problem.

The female squirrel typically has one litter a year, consisting of three to four young. One aspect of the mating ritual, which you may have observed, is an extended chase, mostly among tree branches. The young are born in around 40 days, and they reach full body size in about four months.

If you consider squirrels a pest on your property, you may want to investigate methods for control. Some people resort to shooting them or putting out rat poison. But there are more humane approaches.

One idea is to contact a humane animal removal company. They set traps and remove the squirrels to a remote location. You can find these companies online or in

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