What to do Before Frost in Southern California

Friends, I first must apologize for not getting this posted earlier. We officially had our first freeze this past week, so this is a somewhat reactive blog entry. To be honest, I’ve been preoccupied with other things, so I didn’t even know a frost was coming—-and therefore did not protect my plants from frost! Lucky for you, this created a wonderful learning opportunity to join me in the garden to learn about which crops are frost tolerant, how to protect plants from frost, and what does a plant look like when it has been killed by frost.

The Updated USDA Plant Hardiness Zone Map

Do you know your gardening zone? I’d like to start off with a friendly reminder that you can lookup your gardening zone by zipcode by visiting my blogpost HERE. In fact, the USDA Plant hardiness Zone Map was just updated with new information for 2023—it was last updated in 2012 and 1990. While there are drawbacks to this type of zone system, inevitably the USDA plant hardiness zones are pretty much the standard for how gardening info is presented, organized, and quantified here in the United States. Therefore, it’s important to know your gardening zone (I share more about the WHY and HOW in that blogpost).

One reason this USDA gardening zone map is valuable is because it tells us the lowest average temperatures for our zone/area. This is going to help us understand what plants might need to be covered to protect from different level if freezing.  I’ll be sharing the plants I know will survive light freezes (and the ones that won’t) and the various tools I use to protect plants from frost. To be upfront, most of the concerns I address are specific to Southern California, Orange County, Los Angeles, and San Diego, but the basic principles of frost protection and things to consider would be applicable to other climates as well!

What is a frost or a freeze Exactly?

In Orange County, the coldest we typically get in Winter is 30 degrees F. Of course, microclimates exist all around our cities, and even in our own backyards. For example, one area of your yard could reach 30 degrees, while another stays relatively insulated and never gets lower than 35 or 40 degrees. The only way to know for sure what temperatures are in your yard is to measure with a thermometer. In fact, some gardeners have weather stations that they use to monitor their yards for fun, but I simply rely on checking my weather app, knowing how my home differs from the app, and being familiar with the hot and cold spots in my yard. It really depends on your garden personality….

While frosts and freezes aren’t technically the same, I’m going to reference these ranges for the purpose of this post as they are typically agreed upon by various Master Gardening extensions:

So, I’m speaking from the experience of a gardener who typically deals with things in the “light freeze” category. Furthermore, I can attest that my yard only experiences a handful of light freezes every Winter—it’s not like we have weeks and weeks of freezing temperatures. Does this mean I don’t need to know about frosts? Absolutely not! Ask the multiple papaya trees, nasturtiums, and dragonfruit I’ve killed in the past! Understanding how to protect tender plants from frost is still extremely important, even in a mild climate.

Tender versus Hardy Plants

A second vocabulary term we need to cover is the word “hardy (which also goes in hand with “tender”). Have you read my blogpost about Cold Hardy Annual Herbs For Southern California? If so, you’ll know that hardy plants are plants that have some degree of frost tolerance. Parsley, for example, can withstand light freezes easily and also has been documented to survive very short freezes down to 10-20 degrees! If you’re about to ask yourself “do I need to protect this plant from frost?” you’ll need to consider that specific plant’s hardiness or frost tolerance.

One the flipside, if you’ve still got basil around in January, you most definitely want to cover the plant before a frost. Basil is a great example of a “tender” plant, which means that it is frost-sensitive. Personally, I’m very much a seasonal gardener, so I’ve gotten used to embracing summer basil and saying goodbye to basil in Winter.

Another thing to consider when deciding if you need to protect plants from frost is their growth stage/maturity. In general, young plants can be more frost-sensitive than established plants. The best example I have of this is papayas. One year I planted a bunch of small papaya saplings around one papaya tree we had. After a light freeze, all of my saplings died, but the mature tree only had a few damaged leaves. Additionally, I’ve heard similar accounts from other gardeners in regards to avocados and citrus . Actually, we never cover our citrus before a light freeze because it’s all mature and established trees—I’d feel very different if they were young trees!

How to Protect Plants From Frost In Your Garden

Last week (after we got that frost) I grabbed my camera and went out to document the frost damage in the garden. Since I had forgotten to cover any of my plants, I figured it would be helpful to document what froze and how it thawed out later in the day. Although I wish this information was available to you sooner, I realized that a blog  is built post-by-post, so at least I have the footage/pictures now to act as references in the future. Hopefully none of you had huge losses in your gardens. If you did, my heart is with you, it’s something we have all been through.

Choosing a Frost Cloth to Protect From Frost

Depending on your lowest average temperature, you might want to look at the rating of your frost cloth. If you’re using burlap, sheets, or something not meant for the garden, this won’t matter, but if you plan to invest in some frost cloth you’ll want to take note. 

For example, my original DIY fabric row covers were made from Agribon-15 with only offers slight frost protection. On the other hand, Agribon-19 protects down to 28 degrees and Agribon-30 down to 26 degrees! Depending on your lowest average temperatures for your area, you’ll want to consider the right type of garden fabric for you. Just some food for thought. On a personal note, I had to juggle the idea that we might get cold at night but too hot during the day to leave frost cloth on, especially if I chose a heavier cloth option. 

Last but not least, you can drape cloth over hoops like I do over raised beds, but you can also use cloth to protect individual plants from frost too. You can drape fabric over tomato cages, or even loosely around individual plants—you just want to avoid tightly wrapping or smothering a plant. 

Additional Ways to Care for Tender Plants

Do you have any potted citrus? Depending on your situation, you could opt to simply bring your frost-sensitive/tender plants indoors for the night. Gardeners in much colder climates use greenhouses or bright windows indoors to continue caring for their tender plants through winter. Even placing containers closer to your home can allow the plants to take advantage of any residual heat the walls may hold onto.

Plan ahead! The more you garden, the more familiar you will be with the hotspots or coldest areas of your garden. If you watched my frost damage video, you’ll see that I mention an area of my potager garden (under the tangerine and next to the fence) as being much warmer than the rest of the yard. Our wood fence holds onto heat, plus the tangerine is large enough to create some insulation from cold breezes, and all the plants are pretty close together which created a cute little “cuddle” situation. Haha. What I’m trying to say, is that you can save yourself some time and work by simply planting tender plants in protected areas of your yard and reserving hardy plants for the coldest spots.

Do Not Prune Before a Frost

Can I confess? Snow scares me a little. It’s not the actual snow, but it’s all the knowledge you must have to live in snow—how to drive in snow, prepare your home and pipes for freezing, snow safety, how to plow roads, and how to scoop driveways. If we ever move, I know I’ll need lots of help figuring it all out! But another really interesting thing I’ve learned is that some gardeners trim off dead or damaged parts of plants and trees before a severe snow to prevent the accumulating ice or snow from creating further damage. Apparently, the weight from ice or snow can cause these dead or damaged areas to break or rip out perfectly healthy plants! On the other hand, in mild climates, we are generally advised to never prune before a freeze. Essentially, this is because the plant needs all the insulation possible to protect itself from cold temperatures. Pruning should happen only after the danger of frost has passed for the season. Isn’t that a great example of how gardening can vary from climate to climate?

What to do after a frost or freeze

After we recieved our first frost, I went out to take note of how the plants fared. And guess what? My eggplant bushes all had frost damage on the majority of outer leaves! This is not a surprise, as eggplants are not frost tolerant, but this segues into what to do after you notice frost damage on your plants.

In reality, some plants cannot be saved. Freezes effect plants on a biological level—the cells inside the plant contain water that can freeze and burst or stop the circulation—permanently damaging the plant. Additionally, frozen ground can prevent plants from uptaking nutrients or water, thus killing the plant. This is why mulching can also be important!

On the other hand, for plants that have frost damage but aren’t dead, leave the damaged leaves alone to act as an insulative layer for the plant going forward. For instance, I’ll leave the eggplant alone until after our cold season has passed so that the inner portions of my plant remain protected from further frost.

On a daily basis, you might need to remove blankets, sheets, or other covers that don’t allow in sunlight so that your plants can enjoy the day. I usually remove my covers after the frost has thawed in the morning.

What Plants to I Need to Protect From Frost?

Last but not least, I don’t have an exhaustive list for you, but I can share the common fruits and vegetables that we should think about before a frost arrives:

Out-of season plants: protect any plants that are technically “out of season”—this means peppers, tomatoes, basil, beans, eggplants, or any plants you saved from Summer in hopes of keeping around.

Tender plants/citrus/avocado: Protect tender plants like young citrus, young avocado trees, nasturtiums, dragonfruit, bananas, papayas, lots of tropical fruits, young seedlings.

Cool season crops that can handle light freezes and moderate freezes (for short period of time only) are: lettuce, *potatoes, celery, cauliflower, radishes, turnips, swiss chard, beets, cilantro, dill, carrots. Potatoes tend to be more frost sensitive than the others on this list.

Crops that can handle short hard freezes (aka crops I don’t worry about in Southern California): cabbage, kale, broccoli, brussel sprouts, joi choi, spinach, pansies, parsley, stock, peas

I hope you find this guide helpful in protecting your plants from frost when the time comes. As always, growing seasonally and choosing plants that flourish in your climate are the best ways to mitigate the amount of work that is required of you. It’s when we start to push boundaries and extend our seasons that the challenges can be a little different. Regardless, remember to have fun!