‘Chill’ could almost be a pleasant euphemism for ‘frost’. Both words describe cool or cold weather that occurs during winter. The obvious difference is that one is good, and one is bad. Chill is a minimum duration of cool weather that some plants require through winter to maintain their schedules. Frost is weather that is cool enough to damage some plants.
This technical difference is that chill is at or below forty-five degrees Fahrenheit (≤45°F), and frost is at or below thirty-two degrees Fahrenheit (≤32°F). That is a difference of only thirteen degrees Fahrenheit (13°F), just above the freezing temperature of water. Climate and weather are simply not cooperative enough to comply to such precise technicalities.
Climates that provide sufficient chill for many plants that require it are also likely to inflict frost on occasion. Where chill is sufficient for most plants that need it, frost is likely much too severe for plants that are sensitive to it. Climates that lack frost are unlikely to provide enough chill for plants that need just a bit. High chill apples and oranges should not mix.
Of course, just as various chill dependent plants require various degrees of chill, various frost sensitive plants tolerate various degrees of frost. Some orange cultivars can survive frost as cold as twenty-five degrees Fahrenheit (25°F) within climates that low chill apple cultivars are happy with. Angel’s trumpet though, succumbs as soon as ice crystals form.
It is helpful to know which plants are sensitive to frost, even in frostless climates. Tropical plants might get rather pallid when the weather is too cool for too long, even if frost is not a direct threat. Potted plants are more susceptible to frost damage than they would be in the ground, but can migrate to sheltered situations. Some can be temporary houseplants.
Frost naturally limits the selection of plants. Various tropical plants that are appropriate to frostless climates are not appropriate for climates with harsh winter weather. That can be confusing with so many distinct climates within such minimal proximity. Coastal, inland, mountain, and all climates are so very different from each other.
The Santa Clara Valley was formerly famous for stone fruit orchards. The San Fernando Valley was formerly famous for citrus orchards. The Wenatchee Region of Washington is still famous for apple orchards. Many variables influence which agricultural commodities grow or grew in each region. Of these, one of the more obvious is temperature and ‘chill’.
Citrus could not be productive in the Wenatchee Region because it could not survive the chill of winter there. Although productive in home gardens of the Santa Clara Valley, it is not quite as productive as it is where winter is warmer in the San Fernando Valley. Citrus appreciates warmth but not chill. Many tropical and subtropical plants feel the same way.
However, many of the numerous cultivars of apple that are so famously productive in the Wenatchee Region would be unproductive in the Santa Clara Valley. Only a scant few of these might produce relatively meagerly in the San Fernando Valley. Unlike citrus, which dislike chill, apple trees need chill for production. Some cultivars need more than others.
Chill regulates the schedules of many plants that are originally endemic to climates with cool winters. It confirms the occurrence of winter, which is a convenient time to finish one annual cycle and begin another. Some plants require only a minimal chill. Those that are from climates with harsh winters require coercion by more significant and sustained chill.
One of the primary reasons that spring bulbs are available for planting early in autumn is that some benefit from spending winter in a cool and damp garden. Although, most bulbs are chilled prior to marketing. Some previously chilled spring bulbs bloom splendidly for their first season, but then bloom unsatisfactorily if chill is inadequate for them afterward.
Most plants that need more chill than they can get locally are simply not available locally. Some are available online though. A few locally popular plants that are marginal for mild climates get confused by the seasons. This is why some flowers such as torch lily, bloom randomly or out of season. Daphne and some late winter flowers may be blooming now, and could get damaged by frost later.
Frost is not as much of a concern here as it is in other climates. It is very rare in some of the coastal climates of Southern California. The potential for frost damage increases farther inland, farther north, and at higher elevations. Regardless, it is generally tolerable locally. Even if it is necessary to protect a few marginal plants prior to frost, the ‘average last frost date’ gets little consideration.
The average last frost date designates the end of the frost season for a particular region. Although a specific date, it is an average of dates of the last frost of previous years. It includes minor frost that caused no major damage. Damaging frost, although possible, is unlikely afterward. It becomes more unlikely as the season advances. The process reverses after the average first frost date.
Obviously, average last frost dates are as variable as climates. They are irrelevant for climates without frost. Climates with cooler winters generally have average last frost dates later than those of milder climates. For most of us on the West Coast of California, the average last frost date happens before we are aware of it. Nonetheless, it is helpful to know the date for our particular regions.
Warm season vegetable and bedding plants should be safe in the garden after the average last frost date. Directly sown seed should get all the warmth it needs to germinate. Young plants will not likely experience damaging frost. The weather will continue to get warmer. The days will continue to get longer. Cool season vegetable and bedding plants will relinquish their space as necessary.
Plants that sustained damage from earlier frost can now be pruned and groomed. Damaged foliage that remained in place to insulate inner stems is no longer necessary. Pruning and removal of ruined vegetation stimulates new growth while it will be safe from frost. Aggressively pruning and grooming damaged plants that are already regenerating fragile new growth may be complicated.
Most local climates are beyond their respective average last frost dates. Soon, the others will be too.
As if the lack of rain is not serious enough, the lack of cool winter weather will also cause problems for gardening. Warmth is certainly not as bad as drought, and makes gardening and other outdoor activities more pleasurable, but it interferes with the schedules and cycles that we and the flora in our gardens rely on. Something as natural as the weather should not be so unnatural.
The earlier unseasonably cold weather convinced plants that it really was winter. The problem is that the weather then turned unseasonably warm, and has stayed this warm long enough for plants to believe that it is spring! Some established (not freshly planted) narcissus and daffodils that should bloom as winter ends are already blooming, and some that are naturalized where they get no supplemental watering are already fading from the lack of moisture.
Buds of dormant roses are not staying so dormant, and may soon pop and start to grow. Buds of dormant fruit trees could do the same. When the rain finally starts, it will likely damage and spread disease among freshly exposed rose foliage and newly developing buds. Fungal and bacterial diseases that get an early start will likely proliferate more than they normally do through the following spring. Rain can likewise damage and dislodge fruit blossoms.
The many plants in the garden fortunately have a remarkable capacity for adaptation to weird weather. Bulbs, roses, fruit trees and other plants should eventually recover and get on with life as if nothing happened. The weather is actually more of a problem to those of us who want an early and healthy abundance of roses and an abundance of fruit in summer.
It is still a bit too early to know how the weather will affect what happens in the garden this spring, but fruit production of many types of fruit, as well as bloom of some types of flowers is expected to be inhibited.
Contrary to popular belief, there is a bit of chill during winter here. I was surprised by how many were surprised by my pictures of slight frost last week. The stone fruit that used to grow in the Santa Clara Valley could not have produced without adequate chill. Some deciduous trees color well for autumn, and all defoliate. We do not use much firewood, but some of us use some.
It may not look much like autumn to outsiders. Nonetheless, I find the local climate to be more than satisfactory for what I grow. In some regards, I find it to be ideal. Rhody just stays in by the stove.
1. Sycamores are trashy. Because of anthracnose, they dropped leaves in spring. They dropped more after the Fire. Now they are defoliating for winter. A bulldozer is used for all the leaves.
2. Bald cypress colors well by simple local standards, even if it is merely orangy brown. Bald cypress is rare here, perhaps because of the climate, or perhaps because of its buttressing roots.
3. Dogwood fruit is messy through winter. Surprisingly, wildlife is not particularly interested in it. I should make jelly with it for competition at the Harvest Festival next year (if it happens).
4. FreeBay is how we refer to small piles of bay firewood left on roadsides for neighbors to take away. Vegetation management has become a priority, and generates firewood as a byproduct.
5. Canna behave as outsiders expect them to here. They try to continue blooming until they eventually get frosted. The minor frost they experienced so far was insufficient to stop them yet.
6. Minor frost seems to evaporate as readily as it thaws when exposed to sunlight. This sure looks like autumn. I somehow sort of believe that this is what autumn looks like in other regions.
This is the link for Six on Saturday, for anyone else who would like to participate:
There is not as much difference between the seasons here like there is in other climates. It might seem like we get only summer, with a briefly cooler and slightly rainy time of ‘not summer’. I can recognize the changing of the seasons because I am familiar with them. Those acquainted with more normal climate mind find our subdued seasons to be rather boring, and restrictive.
People from climates with more extreme weather and more pronounced seasons might not expect mild weather and mild climate to be restrictive or limiting. They tend to notice what grows here that would not survive out in gardens through colder winters, such as bougainvilleas, tropical hibiscus and so many of the popular succulents. Even more tropicals survive farther south.
What they do not notice are what does not do so well here. Although stone fruit does remarkably well here, and many apples and pears are more than adequately productive, there are many cultivars of apple and pear that prefer more chill than they could get here. Lilac gets sufficient chill to bloom well here, but not enough to bloom as splendidly as it does in the Upper Midwest.
For example, some might be impressed by the perennial daisies that bloom sporadically whenever they want to throughout the year here. These daisies take no time off for winter, and are rarely damaged by frost every few years or so. They are so rarely without bloom that it is not often possible to shear off deteriorating bloom without removing some of the unbloomed buds.
What goes unnoticed is the potentially subdued bloom of the forsythias, which are so reliably prolific where winters are cooler. Some are real duds this year, and all are blooming notably late. This is one of the consequences of a mild climate.
This really is something that I did not expect to see. It may not look like much. It is just a raspy anemone with bites taken out of it, blooming later than it should. What is so impressive about it is that it was not planted here last year. It was planted during the previous year, then bloomed on time last year, and then died back like anemones normally do. I did not plant it, of course. It is in a planter where volunteers contribute whatever they like.
In case you are wondering why I am writing about it as if I did not expect it to bloom again, I didn’t. For whatever reason, anemones typically bloom well only once here, in their first season after they get planted. They may produce foliage for the following season, or maybe even several seasons, but very rarely bloom again. It annoys me that they are even sold locally. Nurseries should no better than to sell bulbs that do not perform well here.
I have always believed that anemones, like a few other types of bulbs, do not get enough chill in winter to bloom again. This is a rather mild climate. There are certain cultivars of apple that do well where winters are cooler that would be dissatisfied with the minimal chill they would get here. (Incidentally, this last winter was not unusually cold.)
There is also the possibility that anemones can not maintain their foliage long enough through the arid spring and summer weather to sufficiently regenerate their resources to bloom again. The foliage begins to appear in conjunction with bloom, then grows more as bloom finishes, but then dies back as the weather gets warm in spring and summer. The weather is not hot here, but it is rather arid.
We do not get much frost here. This picture of the view through the windshield of one of the work vehicles was taken more than a week ago, while the humidity and the temperatures were still quite low. The sparse and angular pattern of the frost on the windshield is a result of the minimal humidity. There will be more frost later in winter, although there will not be nearly as much as most other climates get.
After a cool Monday morning last week, the weather got a bit warmer, or really just less cool. Rain started about midnight between Tuesday and Wednesday, and continued through the day and into the night. More rain is predicted to start after noon next Tuesday, and continue through Thursday. There will be no frost during this weather pattern. Frost happens here only between rainy weather. One might think that since we do not get much rain, there would be plenty of time in between for frost. Really though, much of our winter weather is simply quite pleasant, neither rainy nor frosty.
As appealing as this might be to those in harsher climates, it has certain disadvantages.
So far, there was just enough chill to start defoliation of the black locusts and box elders in the background of the picture, and just enough rain to almost finish it. Trees that need more of a chill to start this process are not so impressed with the weather. Many of the crape myrtles have not even started to color yet. Cottonwoods are starting to defoliate, but are doing so while still only dingy greenish yellow because they did not get enough chill for better color.
Spring bulbs that got planted earlier or are being planted about now will bloom next spring because they were so optimal and primed to do so before they were planted. However, many will not get enough chill in their second winter to bloom again. Consequently, many of the bulbs that would be perennial in other climates are grown as expensive annuals here. Likewise, seed of certain specie that self sow may not get enough chill through winter to germinate next spring.
So again, what is comfortable for us is not so ideal for everything in the garden.
Where winters are cooler, the deteriorating stems of flowers that bloomed last year either got pruned away already or got knocked down by the weather, and are now rotting on the ground. Around here, where the weather is milder, and some flowers only recently finished blooming, used up flower stalks still stand in stasis. Most but not necessarily all should get pruned out and raked away.
Dahlias succumb to frost as soon as it arrives. If not already cut back, they fall to the ground like steamed spinach, and should get raked up and put into greenwaste. There is nothing to salvage. Sunflowers are related to dahlias, but do not collapse so easily. Even if they are not pretty, those that produce seed can be left for whatever birds like to eat them, and then recycled when empty.
Of course, not all of the seed must be left to the birds. Some or all can be saved for next year. The flowers only need to be allowed to dry so that the seed matures. If the birds start to eat them first, old flowers can be cut and stored in open bags or boxes in a shed or garage, out of reach of birds. Stems should be cut longer if they are still green. Seeds should fall from the flowers as they dry.
Seed can also be collected from lily-of-the-Nile and African iris, although these perennials are so easy to propagate by division that growing them from seed might be more trouble than it is worth. Their seed capsules must be allowed to dry, just like sunflower seed. Belladonna lily makes a few weirdly succulent seed that are worth collecting. Some primitive cannas make weirdly hard seed.
It might be worth researching flowers that happen to be in the garden to determine if they produce viable seed worth collecting. It is also important to know what seed requires scarification or stratification. Seed that needs stratification must be exposed to cold temperatures to be convinced that it is time to germinate in spring. Canna seeds need to be scarified by filing through the hard shells before they germinate. Other seeds need other types of scarification or stratification.