- Author: Brent McGhie
By Brent McGhie, Butte County Master Gardener, January 6, 2017.
Plummeting winter temperatures often lead to frost damage in plants. The damage occurs when ice crystals form within plant tissue, damaging their cells. Leaves and tender new growth are usually affected first. Initially, they will appear wilted. Then the wilted growth will turn brown or black and eventually become crispy. This means these affected parts of the plant have died.
It is tempting to remove frost-damaged plant growth immediately, but dead material should be left on the plant until the full extent of the damage is apparent in the spring. There are several reasons to wait. By allowing plenty of time for new growth to appear, the extent of any damage will be clearly apparent and it will be less likely that you will accidentally remove living tissue that survived a freeze. Additionally, dead material can actually provide an insulating effect and removing it too soon may expose additional tissues to future freezes. If you prune out dead material before another freeze hits, it is more likely that an even greater portion of the plant will be killed. In Chico and nearby areas of the valley floor, the danger of frost is usually over in late April, so it is prudent to wait at least until then, or later, before doing any pruning.
In citrus, if hardier growth (such as twigs or wood) has not been seriously damaged, it is normal for dead leaves to be rapidly shed. If the frost-killed leaves remain on the plant, this is an indication that twigs or branches have been seriously damaged. If larger branches or the trunk of a tree sustain cold damage, the bark will split and dead patches of curled, dry bark may appear. If a young citrus tree has been killed nearly to the ground, inspect it closely to determine if the damage extends below the graft union. The graft union is the junction where the fruit-producing part of the tree was grafted onto the rootstock. If new growth comes only from the rootstock, the tree will no longer be true to the type you originally planted and will usually be unproductive. In this case, the tree should be replaced or you can try your hand at budding a new top variety into the rootstock sprouts in late spring.
The only thing that should be done immediately after frost damage has occurred to citrus and other woody plants is whitewashing. Whitewash should be applied to the trunk and exposed limbs. This protects the bark from sunburn, which is more likely to occur if a plant becomes defoliated. Frost-damaged plants are more susceptible to disease and insects and sunburn increases this susceptibility. To make whitewash, mix equal parts of white interior latex paint with water. If the area to be painted is particularly rough and fissured, a thinner mixture can be applied for better penetration and coverage. You can dilute a thicker top-quality interior latex paint as much as 2:1 or 3:1, water to paint.
It is also important to note that frost-damaged plants are unbalanced: although their leaves have been reduced, they still have the same root system. This can result in extensive new growth over the entire plant once regrowth begins in the spring. To ensure that the plant reaches an acceptable balance between its leaves and its root system, the new shoots should grow at a moderate rate. It is recommended that little or no fertilizer be applied to these plants initially, and they should be irrigated less than usual until they have returned to a normal appearance. Too much nitrogen fertilizer, for example, can encourage sucker and water sprout growth, while too much water can damage roots.
Of course, it would be preferable to prevent frost damage from occurring in the first place. To read more about preventing frost damage and many other gardening topics, visit the Butte County Master Gardener website (http://ucanr.edu/sites/bcmg/). For specific information on frost protection, the following link will take you to our Real Dirt blog page on this topic: Frost Protection for Citrus
See also:
By Laura Lukes, Butte County Master Gardener, January 20, 2017.
These workshops are designed for the home gardener interested in creating sustainable landscapes, starting plants from seed, harvesting rainwater, learning propagation and composting techniques, and much more. A total of nineteen workshops are scheduled between February 9th and June 14th. All workshops are free of charge, with one exception: there is a small materials fee for the May 9th “Building Compost Bins” workshop.
“We are particularly excited about the new topics we've added, and the quality of our presenters,” added Ms. Perkins. “In addition to our knowledgeable Master Gardener speakers, this year we have partnered with local experts” for the workshops on worm composting at the Durham Worm Farm, hardscape materials at the Sutherland Landscape Center, and the Native Plant Walk on the CSU, Chico campus.
The primary venue for these workshops is the Master Gardener Demonstration Garden, located at the Patrick Ranch Museum on the Midway south of Chico. The Demonstration Garden features plants that thrive in a Mediterranean climate, and are particularly well suited for our conditions in Butte County. All of the plants in the Demonstration Garden do well in hot, dry summers with little water, and provide habitat for local wildlife, especially various pollinators. The Audubon Society has certified the Demonstration Garden as a wildlife habitat. In addition to the Demonstration Garden location, some of the workshops will be held inside Pat's Barn at the Patrick Ranch Museum, and a few will take place at private residences. Details are available on the website.
The workshops are listed below. Registration is required at www.ucanr.edu/sites/bcmg/events/workshops. Due to space considerations, registration is limited.
- Thursday, February 9: Worm Composting, 1 – 2:30 PM
- Saturday, February 11: Mason Bees, 10 – 11:30 AM
- Saturday, February 11: Removing Your Lawn, 1 – 2:30 PM (NEW)
- Wednesday, February 22: Weed Identification and Treatment, 1 – 2:30 PM (NEW)
- Wednesday, March 15: Practical Rainwater Harvesting, 1 – 2:30 PM (NEW)
- Thursday, March 16: Propagation, 1 – 2:30 PM
- Friday, March 17: Hardscapes in the Landscape, 10 – 11:30 AM (NEW)
- Wednesday, March 29: Drip Irrigation, 10 – 11:30 AM
- Thursday, April 6: Espalier Demo Garden, 2 – 3:30 PM (NEW)
- Monday, April 17: Composting, 10 – 11:30 AM
- Thursday, April 20: Grafting Fruit Trees, 10 – 11:30 AM (NEW)
- Saturday, April 29: All About Backyard Fruit Orchards, 10 – 11:30 AM
- Thursday, May 4: All About Backyard Fruit Orchards, 10 – 11:30 AM
- Saturday, May 6: Native Plant Walk at Chico State, 1 – 2:30 PM
- Tuesday, May 9: Building Compost Bins, 10 – 11:30 AM
- Wednesday, May 10: Prune Demo Garden Orchard, 10 – 1:30 AM
- Wednesday, June 7: Basic Garden Design, 10 – 11:30 AM (NEW)
- Wednesday, June 14: Raised Bed and Hoop House, 10 – 11:30 AM (NEW)
Butte County Master Gardeners are University of California-trained volunteers whose purpose is to extend research-based knowledge and information on home horticulture, pest management, and sustainable landscape practices to the residents of Butte County. California's Master Gardener Programs are part of the University of California's Division of Agriculture and Natural Resources. Butte County Master Gardeners offer garden advice and assistance through their Hotline at 538-7201, at select community events, and at the farmers markets throughout Butte County. Please visit their website to find out more about them and their educational programs: www.ucanr.edu/sites/bcmg.
The Master Gardeners look forward to seeing you at their workshops, tours, plant sales, and other educational events and venues!
Brent McGhie, Butte County Master Gardener, February 3, 2017.
Western flower thrips are tiny insects. Adults are only 0.8 – 1.4 mm long. They range in color from dark brown in the spring to a lighter white and yellow form that is prevalent during the rest of the year. They are hard to spot because of their minute size and their habit of sheltering inside flower and leaf bud scales. Thus, a history of thrips-damaged fruit may be a better indicator of the presence of thrips than actually seeing them.
The tan or silvery, scabby scarring caused by thrips does not significantly harm the internal quality of the nectarine fruit, but the scarring is unsightly and has a coarse, leathery texture that is unpleasant to bite into. Fruit damage occurs when immature thrips nymphs feed on the surface of tiny fruit, just as it begins to develop. Feeding creates scars on the fruit surface and these scars enlarge as the fruit grows. These insects often begin feeding even before the flower petals have dropped from the newly forming fruit. Once fruits begin to enlarge and their skin becomes tougher, thrips start to feed on new tender leaves as leaf buds begin to open. Unfortunately, this means that by the time their damage is apparent, thrips may no longer be present on the fruit.
Western flower thrips are not easy to control. They overwinter as adults in weeds and grasses beneath fruit trees or in nearby fields. If these overwintering sites are disturbed (by mowing or cultivating, for example), the thrips have a tendency to migrate onto nearby fruit trees. The first line of defense in controlling thrips is to keep the area around fruit trees clean and weed free in the first place. If possible, nearby fields should be disked or mowed in the fall to further deny thrips a habitat for overwintering.
Another way to control thrips is to encourage their natural enemies. Green lacewings, predatory thrips, minute pirate bugs and tiny predatory wasps are among the beneficial insects that prey on western flower thrips. To encourage these beneficials, keep dust to a minimum and consider rinsing dust off plants. Also, avoid persistent pesticides because these chemicals harm beneficials as well as the targeted pests. In addition, it should be noted that the greater the diversity of plant species in the garden, the greater are the odds of providing a suitable habitat for beneficials. A final thing to note about biological control is that releasing natural enemies is unlikely to provide significant thrips control. In most situations, beneficials simply disperse soon after they are released.
If the cultural and biological controls described above do not provide adequate control, they can be used in conjunction with the most selective, least toxic insecticides available. Contact insecticides that do not leave persistent residues include insecticidal soaps, horticultural oils and neem oil. These oil sprays must thoroughly cover the affected trees and be used at the right rates to avoid phytotoxicity (toxic effects on plant growth). These products can also be harmful to natural enemies and pollinators, so the timing of their application is important. For example, spraying just after flower petals have dropped will limit how much exposure bees will have to these materials.
A somewhat more effective spray is spinosad, which is sold as Captain Jacks' Deadbug Brew, Green Light Lawn and Garden Spray with Spinosad 2, or Monterey Garden Insect Spray. Spinosad is toxic to certain natural enemies and to bees, so should not be sprayed when trees are flowering. As with any chemical control, be sure to read and carefully follow label directions. Avoid using organophosphates such as malathion, as well as carbaryl, or pyrethroids as these chemicals are highly toxic to beneficial insects and are not particularly effective against thrips.
For further information:
- UC IPM: Nectarine: Western Flower Thrips
- UC IPM: Pest Notes: Thrips
- OnTario Tender Fruit IPM: Western Flower Thrips
Photo credit: OnTario Tender Fruit IPM
By Barbara Ott, Butte County Master Gardener, February 17, 2017.
The current emphasis on water-wise gardening has created an interest in succulents. All succulents are able to store water and food in their leaves, stems and roots. These stored nutrients can be released when needed. This makes them drought tolerant. Succulents require good drainage, deep but intermittent water, bright light, and good air circulation. The soil should be open and airy with low organic matter.
Many gardeners grow succulents in the Crassulaceae family. Among the most popular are Echeveria, Graptopetalum, Aeonium, and Sempervivum. Echeveria, Graptopetalum, and Aeonium are hardy to USDA zones 9-12 (Or Sunset zones 8, 9, 12-24); while the hardier Sempervivum can thrive in a broader range, down to zone 5 (or Sunset zones 2-24, according to the Sunset Western Garden Book).
Because many purchased succulents are unmarked, while others are given by friends as cuttings, it can be difficult to know the genus of a particular plant. This is especially the case because the genera of Echeveria, Sempervivum, and Graptopetalum are similar in appearance. However, careful observation will aid in identifying succulents. First, look to see if the succulent is spiky or chubby, and whether it forms rosettes. What is the shape of the leaves? Look at size, texture, and color. Notice if offsets hang from the edges of a rosette, or attach to its center.
Echeverias are valued for their colors and variations. Native to the Americas, their rosettes range in size from three-quarters of an inch to 20 inches in diameter. Echeverias have thicker and wider leaves than Sempervivums. While both include varieties commonly called “hens and chicks” they are from different genera. The leaves of Echeveria are spoon-shaped, and gray, green or bluish in color. These plants flower in the warmer months. Their bell shaped flowers appear on stalks that rise up through the leaves, and can be white, orange, pink, or red. Echeveria offsets (chicks) grow out from a single base stem and form clumps.
Sempervivums are native to Europe. Their value as talismans is reflected in their name semper (always) and vivus (living). This reputation comes from their ability to survive in freezing weather while their leaves stay green. Sempervivums are commonly called Houseleeks or Hen and Chickens. Open rosettes range from one to five inches across and form clumps to two feet or wider. The leaves of Sempervivum are narrower than those of Echeveria, they have pointy tips, andaregray-green to red-brown in color. Small, pink, red, or orange star-shaped flowers arise on fleshy stems to 10 inches tall. These succulents reproduce from offsets attached to a stolon (a stem that can take root).The stolon breaks easily, allowing the tiny offsets to roll away before forming roots.
When looking at “mystery” succulents think in terms of leaf shape, color, and thickness. Then look to see if there are offsets. Are the offsets located on stolons or attached to a main stem? Watch for flowers and see if they are bell shaped or star shaped. All of these characteristics will provide information about the genus of the “mystery” succulent.
Photo credits: Wikipedia Commons
Table for identifying Echeveria, Sempervivum, and Graptopetalum:
Characteristics of common varieties |
Echeveria |
Sempervivum |
Graptopetalum |
Origin |
North & South America |
Europe |
South America |
Rosette size |
3/4”-20” diameter |
1”-5” diameter |
2”-5” diameter |
Offset Spread |
spread from a main stem |
clumping, stolon held |
rosettes break off from root |
Leaves |
thick & spoon-like |
narrow & pointy |
thickest & rounded |
Leaf color |
gray-green, bluish |
gray-green, red-brown |
chalky gold or green |
Flower shape |
bell shaped |
star shaped |
star shaped |
Flower color |
white, orange, pink, red |
red, yellow, pink |
white/red, yellow |
Flower growth pattern |
on stem amidst leaves |
on stolon from center |
stem from center |
Common name |
Hen & Chicks |
Hen & Chicks |
Ghost plant |
Table created by Barbara Ott
By Carol Koenig, Butte County Master Gardener, March 3, 2017.
Mason bees look similar to house flies – they have black bodies and a dark blue iridescent sheen. One advantage for the family backyard is that the males do not have a stinger and the females will only sting if trapped or squeezed.
The mason bee is a solitary bee which lives in natural cavities such as woodpecker holes or hollow stems. They also seem to be just as happy in artificially-constructed nests, so long as these nests include tubes made of cardboard or paper where the female bee can lay her eggs.
Purpose-built nests, often called bee boxes, are set out in early spring when daytime temperatures regularly reach 55 degrees. The bee box is placed outside, facing south in a location that is sunny but protected from wind and rain. Because mason bees will not fly farther than three hundred yards from their nest, bee boxes must be located within range of fruit trees and flowering plants.
The bees emerge from their home in early spring when fruit trees start to bloom. The males emerge first, waiting for the females. When the females come out they quickly mate and start work on their nests for the year. They begin by finding a suitable hole and then start to gather pollen and nectar from nearby trees and plants.
The mason bee gathers pollen on her underside. As she zig-zags among the blossoms she is picking up and dropping off pollen, thus pollinating the flowers as she travels. One mason bee can pollinate 2,000 blossoms in a single day. She brings pollen back to her nest and deposits it at the back of the tube, making a mound on which she will lay one egg. She then seals the space off with mud to create a cell. It is because they use mud in their nest construction that they are called mason bees.
The female mason bee starts another nesting cell and continues until the nesting chamber or tube is filled with a series of egg cells. Amazingly the bee is able to determine, before she lays an egg, whether that egg contains a male or female larva. She will lay female eggs at the rear of the chamber, for protection, and put the male eggs up front. Finally, she seals off the front of the tube with a mud plug.
All this activity can be closely watched since the bees don't sting. The female can be seen heading into her chamber when she is laden with pollen, and backing into her chamber when she is about to lay an egg. Sometimes she just likes to rest in the front of the chamber. This activity continues for six to eight weeks, and then the mother bee dies.
Mason bee larvae hatch a few days after their eggs are laid. The larvae eat the pollen the mother has provided and then each larva goes into a pupal stage. The following spring, the adult bees emerge. The males emerge from the nest first, the females follow, and the process begins all over again.
If you would like to learn more about these bees, local mason beekeeper and Master Gardener Tom Hansen will be speaking about them at Hodge's Nursery in Durham on March 11, at 10 a.m.
More information on mason bees can also be found at Crown Bees
Instructions for building your own bee box can be found at National Wildlife Federation's Garden for Wildlife.
This article is based on information provided by Tom Hansen, local mason beekeeper and Butte County Master Gardener, and a talk on mason bees given by Susan Morrison, Contra Costa Master Gardener, in 2013.