by Mel Kendall

How many of you have gone to bed only to kick yourself in the morning when you get up and see a white, icy garden and have to face the frost damage to your plants? 

Frost does sneak up, that is a given. You can prepare ahead of time for frost and avoid much of that "kicking yourself" part. The first and easiest way to avoid this is to keep a regular watch on the weather forecasts. It's the weather, after all, and it changes daily.

Another way is to plan your garden accordingly.  Avoid planting frost tender plants in low areas of the landscape. These areas are where cool air will pool and create cold microclimate areas.  Frost tender plants, like citrus, in a protected area. If planted next to a south or west facing wall these frost tender plants will benefit from the residual heat radiating off that wall at night. Choose plants native to our area as they are prepared for our region's temperatures. Some cold hardy plants are crocus, pansy, tulip, calendula, sweet alyssum and snapdragons. Cold hardy veggies, that actually taste better when touched by frost are carrots, potatoes, beets, parsnips, turnips, onions, garlic, radish, rutabaga, broccoli, cauliflower, kale, brussels sprouts, cabbage, bok choy and collard greens. Along with those veggies that benefit from frost some fruit tree varieties actually need a number of chill hours to produce a good crop.

Keeping our plants hydrated will also fend off the effects of cold weather. If you water during the heat of the day the moist soil will insulate the plant's roots and the rising heat of the water evaporating will help to warm the foliage at night. Succulents are an exception as their leaves are normally full of liquid and are more susceptible to freezes even without additional water

Covering any bare soil with mulch will protect soil from sudden temperature changes. A thick 1-4 inch layer of mulch around and an inch or two from the main stalk of all the plants will provide insulation for those plants' root systems and protect the soil as well.  

Cover any frost sensitive plants in the evening and uncover after the frost has passed will provide further protection for plants. Cover smaller plants individually with bell shaped covers made of plastic or glass. Plastic milk cartons with the bottoms cut out work quite nicely. Cover larger plants with blankets, sheets, drop cloths etc. Use stakes or pvc hoops to hold cover away from the foliage in a tent-like formation that falls almost all the way to the ground. Leave the bottom of the covering open to the ground.  Keeping the cover off the foliage will prevent the frost laying on it from transferring cold to the plant's leaves and freezing them. This may not be possible with larger trees and shrubs, so cover the bulk of the foliage as much as possible.  Many purchased covers offer a drawstring at the bottom. Do not cinch the bottom of the cover shut because as the soil cools it will release its heat up into the opening of the covering and help to warm the plant.  Weight the edges or clip the cover to the support structure so it doesn't blow off during the night. Plastic isn't a good material for the cover as it doesn't breathe.  All of these coverings should be removed in the morning when the temperature has warmed.  

If frost is the normal state of things in your area you can purchase plant frost protection covers specifically designed to be left in place throughout the season. They can be cut to size and have a large weave. They are designed to allow sunlight and heat to enter during the day, and protection from heat loss and frost damage during the night.  

If frost is predicted, bring small container plants and any hanging pots inside in the evening and then put them back out in the morning. Place them inside to a cool, not a heated location like a garage, garden shed or basement, after the sun sets in the evening. These potted and hanging plants are more susceptible to cold and root damage because they are surrounded by air and not down in the insulating soil. Put the plants back out after the frost in the morning. 

Air movement is important to frost protection. In Napa Valley the sound of vineyard fans are common in winter months. This air movement can actually raise the air temperature as much as 2-7 degrees. Small home gardeners don't have huge fans, but we can move the air in our gardens using small electric fans placed on a raised platform to blow over frost sensitive plants. Remember, safety first, use only equipment that is rated for outdoor use.  

Add a little ambient air warmth by using strings of old-fashioned Christmas tree lights.wrapped around the trunk and lower branches of trees or a 100 to 150 watt spotlight aimed up into the foliage under but not touching the frost protection cover. Use incandescent light bulbs only. LED lights don't put out heat. Put lights on timers to come on at dusk and go off after warming in the morning. Again, remember to use only outdoor rated equipment.

If a frost warning is missed, what's a gardener to do? Wait. Wait. Wait. Frost damaged plants often display softened translucent leaves as well as blackened and/or brown foliage and stems. This is a result of the cold air actually freezing the cells in the leaves of the plants. As the liquid expands as it freezes these cell walls will actually burst releasing the liquid when it thaws. The last frost date for our area is around April 15th.  Wait until the weather warms before cutting away any frost damaged foliage. Frost damaged leaves and branches actually help protect the new spring plant growth from further frost damage. After the last frost, wait at least a month before removing dead foliage to give the plant a chance to come back. 

I have quite a few "walking wounded" in my garden as I live in a cold sink microclimate and get more frost than is usually predicted for our area. Being very fussy about my garden's neatness and perfection, these damaged plants are really a sore spot. I plan on taking my own advice and waiting for the spring growth to see which ones have survived my miscalculations. Each gardening adventure is a learning experience.

Napa Master Gardeners are available to answer garden questions by email: mastergardeners@countyofnapa.org. or phone at 707-253-4143.  Volunteers will get back to you after they research answers to your questions.

Visit our website: napamg.ucanr.edu to find answers to all of your horticultural questions.

Please see the our website napamg.ucanr for events including the Las Flores Community Center where instructional events are planned for the last Saturday of the month through 2022. Topics will center on research-based horticultural and climate change issues by featuring water saving plants and soil care. Join us each month at the Las Flores Learning Garden 4300 Linda Vista Ave. for these public education events. 

Photo credits: Mel Kendall

Frost prevention information links:

UC ANR https://mgsantaclara.ucanr.edu/frost-avoidance-and-dealing-with-damage/

https://ucanr.edu/sites/mgscc2016/files/360387.pdf

UCMG Napa County https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=25850

UCMG Sacramento County https://sacmg.ucanr.edu/Frost_Protection/

 

by Rainer Hoenicke

It's early February when I write this, and it feels like May. Even the most ardent climate-change deniers are wondering if they may have to adjust their perception of reality.

October and November were, fortunately, not fire-months in our region, but we received more rain during the last three months of 2021 than we did in all of the 2020 water year. The City even closed the Oxbow Commons flood gates for a short period when the October atmospheric river hit. Alas, the deluge was followed by a record for the City and County of San Francisco for the most consecutive days of no precipitation during the rainy season. I had to periodically irrigate my patio pots and a few newly planted starts for the last two weeks, and our daytime temperatures are almost 20 degrees above normal. What can we, as avid gardeners, do to respond to what appears to have become a completely unpredictable climate with the largest rainfall variability on earth (according to the US Geological Survey)?

One of the Master Gardeners' mission areas is to “…extend research-based knowledge on sustainable landscape practices, with focus on healthy families and communities and sustainable natural ecosystems.” Our own gardening activities have contributed to keeping mentally sane (at least most of us) during the pandemic, but have we ever considered that our gardening and educational efforts may have benefits far beyond our own fence lines and affect well-being and public health decades into the future? The proverb attributed to ancient Chinese wisdom, stating that the best time to plant a tree was 20 years ago, and the second-best is today, seems to be truer today than it ever was, with climate-change effects impacting all of us. But more importantly, we may want to add to the Chinese proverb that the best way of gardening is to keep future generations in mind and the second best is to cherish and sustain the trees that live under our stewardship today. 

When I went on a hike with my dog on a particularly glorious and clear morning at Alston Park recently, I looked out toward Mount George and was struck how well hidden the city landscape is under the extensive tree canopy and thought about the benefits trees provide that go beyond mere beauty and sense of well-being. I began to look at that city tree canopy from a climate change perspective and began to do some research of how much carbon is tied up in the biomass of the urban forest, including both public parks and streets, and also mature backyard trees on private lots.

Usually, more than half of a tree's total weight is below ground, where the roots form a dense network of living carbon that benefits and is part of the complex soil ecosystem essential to soil fertility and health.

As one example of a native tree species we are all familiar with, coastal redwoods remove and store more carbon from the atmosphere per acre than any other forests on the planet, including tropical rain forests, according to recent research.  My own backyard grove of five Sequoia sempervirens trees that appears to have originated from root sprouts of a much larger, single tree decades ago is tying up as much as 4,000 pounds of atmospheric carbon dioxide per year in their roots, trunks, and branches. I used the Tree Carbon Calculator of the US Forest Service's Pacific Southwest Research Station  (https://www.fs.usda.gov/ccrc/tool/cufr-tree-carbon-calculator-ctcc) to come up with this estimate via a simple spreadsheet model that everyone can use easily.

Our oaks are likely not far behind in storing carbon and compensating for carbon dioxide emissions. If we want to reduce or even just stabilize temperatures in this time of rapid climate change, keeping our urban forests intact and growing is an action we can all contribute to. Many other large tree species that are not native occur in our urban forest but equally provide many benefits to public health, wildlife habitat, water and air quality, as well as property values. I found out that in the City of Napa, the only trees that receive some protection on private property is restricted to native trees on parcels greater than one acre. However, private property-owners may nominate any of their trees to become part of the “Napa Registry of Significant Trees” (https://www.cityofnapa.org/DocumentCenter/View/5659/Significant-Trees-Nomination-Packet-PDF?bidId=) to be designated as such by the City Council, so they can be preserved with all their benefits and recorded on the property's deed. Once recorded, a Significant Tree can only be removed if a permit is obtained that meets criteria outlined in the Napa Municipal Code. Every gardener and land steward may want to consider protecting “significant” trees, often taken for granted, and meet the great challenge of keeping our place livable for future generations.

Napa Master Gardeners are available to answer garden questions by email: mastergardeners@countyofnapa.org. or phone at 707-253-4143.  Volunteers will get back to you after they research answers to your questions.

Visit our website: napamg.ucanr.edu to find answers to all of your horticultural questions.

Photo credits: Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0) Wally Gobetz

Information links

UC Davis Climate lab https://www.universityofcalifornia.edu/climate-lab

University of California Climate Change https://www.universityofcalifornia.edu/subject/term/climate-change

 

by Cindy Kerson

I'm back again to report on the progress of the Kurapia replanting area. The original post in Spill the Beans was on December 6,2021. The saga began in April of 2020 when we laid Kurapia (Lippia nodiflora) sod. Over the summer months, it looked beautiful, but we noticed a lot of Kentucky bluegrass (Poa pratensis) growing in spots. It continued to spread, as bluegrass is known to do, a positive aspect if one desires bluegrass. We didn't. We wanted Kurapia. After some discussion, our distributor graciously agreed to return the next spring and replace the sod. Spring of 2021 rolls around and we were in the midst of a profound drought. Once Kurapia is established, it needs very little water – maybe once a month from June to September. But initially it needs a good deal of water, applied frequently to get established. We decided to put off replacement another year. We hope to get more rain so it will be feasible for us to get it started.

Starting in November 2021, whenever we received a shipment with a big cardboard box, I started sheet mulching the area to be re-sodded. It took about 2 months to receive a sufficient number of usable boxes to cover the area. Over two days, I watered the area deeply so the cardboard would be very wet. Then I spread 4mm clear plastic over the top to solarize it. Solarizing is a way to kill unwanted weed seeds. According to UCANR, this is mostly true for annuals since perennials have deeper plant structures (roots, rhizomes) that are present throughout the year. They won't be as threatened by the heated upper layers of soil. The bluegrass is a perennial, so my experiment may not have killed it, but it should be effective against the other weeds in my soil. I think we got most of it up when we pulled up the Kurapia anyway. I get a lot of clover and I've been trained to not pick it since whenever it's shaken (by walking on it or pulling it out), it sprays seeds. In fact, if you get close to it, you can hear the tiny seeds being sprinkled. I recently learned that killing/removing weeds can be detrimental to our ecosystem since those weeds may be pollinizers and/or food and shelter for many insects that are in turn food for larger insects and vertebrates. For me, gardening is primarily to support nature and to provide food, but I am also guilty of manipulating it for my aesthetic comfort and as with everything – it is a balancing act.

I anchored the plastic with either metal garden stakes or rocks. I hope they withstand any winds we have and am curious about what will happen when it rains. That area is on a very slight slope, and I wonder if water will puddle and render the plastic too much of a mess to reuse, since I try to use as little plastic as possible. When the new Kurapia comes, we'll remove the plastic and lay the sod right over the sheet mulched area.

There is a second smaller area that we will re-sod where we did not put cardboard or mulch down. I was going to spread compost, but when we dug up the remaining Kurapia, mostly dead or dormant, the soil was so dark from the compost we put down 2 years ago that we simply put plastic on top. We didn't want to put down mulch because we likely would have had to rake it all out in a few months when we laid the new sod since it would not decompose in time. Just like everything in my garden, it is an experiment. I wonder if the cardboarded (I had to convince spell-check that that is a word) area will do better than the un-cardboarded area. Stay tuned. I'll post next if and when (pray for rain) the Kurapia sod is installed this spring.

Napa Master Gardeners are available to answer garden questions by email: mastergardeners@countyofnapa.org. or phone at 707-253-4143.  Volunteers will get back to you after they research answers to your questions.

Visit our website: napamg.ucanr.edu to find answers to all of your horticultural questions.

Photo credits: Cindy Kerson

Information links:

Oregon State Univ.-sheet mulching (lasagna composting) https://extension.oregonstate.edu/gardening/soil-compost/sheet-mulching-aka-lasagna-composting-builds-soil-saves-time

UC Davis-Kurapia https://ccuh.ucdavis.edu/kurapia