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Frost Protection

For many species, frost damage is not as bad as it looks.

            My colleague in the Los Angeles area still sends me seeds for all sorts of strange plants that I probably should not be growing in my less climactically temperate garden, making it difficult to conform to the primary rule of frost protection: ‘Select plants that are appropriate to the particular climate.’ No matter how often I remind my clients of this rule, I really do not want to abide by it. There are just too many interesting but inappropriate plants.

            So the next option is to grow frost sensitive plants in containers that can be moved to sheltered areas prior to frost. That worked while I had an extra parking space in the carport and some room under the porch for giant bird-of-Paradise, plumeria, philodendrons and such. Eventually though, some of these plants get too large to be contained; and I really do not want to keep pruning them back. Besides, I prefer to grow things in the ground.

            The third option is to put sensitive plants in spots that are naturally warmer, or where they are sheltered below the canopies of large evergreen trees, lath or wide eaves. Just remember that plants under eaves are also sheltered from rain, so may need to be watered occasionally through winter. Steep slopes are not quite as cold because cold air drains off. However, flat areas below slopes get colder as they catch cold air that drains from uphill. South facing exposures are of course warmer than northern exposures.

            I know probably better than most that there are always some plants that are not ‘appropriate to the particular climate’, that I do not want to grow in pots, and that prefer to be out in exposed parts of the garden. For example, bougainvilleas are somewhat tender, have sensitive roots that do not like to be confined, and really want to be out in the open to take advantage of warming sunshine during summer. Such plants in colder areas will either need to be protected, or will get damaged by frost.

            Burlap suspended above the foliage by stakes is typically enough to protect sensitive plants from frost. I have used old towels and linens where my neighbors can not see. Plastic sheeting is also effective, but should be removed before sunlight warms the air too much underneath. Paper grocery bags or cardboard boxes are enough for small plants.

            I actually allow some of my larger plants that would be difficult to cover to get damaged by frost, and then prune out the damage later. If they are too big to cover easily, they are probably big enough to survive frost. Damaged stems should be left until the end of winter both to insulate stems below, and also because early pruning stimulates new growth that is even more sensitive to frost. 

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Frost Is Not An Enemy

Among canna, frost damage is harmless.

Rain was one clue. Cooler weather is another. It is now so late into autumn that it will be winter soon. Every regional climate experiences some degree of chill. Some, particularly to the north, experience frost. This limits gardening in two ways. Several species prefer a bit less cool weather. Several prefer a bit more. Every species prefers a particular range.

Apple trees, for example, require vernalization, which is a specific duration of chill. Some cultivars require more than others. Without it, they can not distinguish seasons, so do not know when to bloom for spring. Consequently, few cultivars of apple perform adequately within Los Angeles. However, many perform very well in the cooler climates of San Jose.

Banana trees, conversely, need no chill, and are instead set back by frost. Some tolerate a bit more chill than others; but ultimately, they are all tropical species. They produce fruit only within the months between frosts. Consequently, not many banana trees are notably productive within San Jose. However, they perform better in the climates of Los Angeles.

Banana trees stop growing when the weather is cooler than fifty degrees or so. That is a bit too much chill for them. However, frost does not occur until the weather is cooler than thirty-two degrees. Banana foliage can therefore be safely dormant during chilly weather. That is a range of twenty-two degrees. Different tropical species survive different ranges.

The simplest form of frost protection is to not cultivate species that are vulnerable to frost. This is, of course, a bit too restrictive for many who enjoy gardening. Instead, some grow vulnerable species in pots to move to shelter prior to frost. Some simply grow vulnerable species below the shelter of eaves or big trees. Tenting may also be effective protection.

Alternatively, some species can endure frost damage to recover during warmer weather. If possible, outer foliage that succumbs to frost should remain through winter. It insulates inner growth from subsequent damage. Besides, premature grooming can stimulate new growth that is more vulnerable. Many perennials prefer cutting back after winter anyway.

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Bulbs For Spring Start Now

Ranunculus will bloom for early spring.

Summer bulbs, such as canna, calla and dahlia, can wait until spring. They do not enjoy winter chill during their dormancy like spring bulbs do. Spring bulbs become available at nurseries now because this is the time to plant them. They wait patiently for winter to end before blooming. A bit of winter chill actually helps them to maintain their strict schedule.

That certainly does not mean that their strict schedule is not adjustable. Most early bulbs prefer interment into their shallow graves within weeks of Halloween. However, they can wait as late as New Year’s Day. This allows for successive planting, which prolongs their ultimate bloom. Early planting promotes early bloom. Late planting promotes late bloom.

Most spring bulbs from nurseries are prechilled because winters are relatively mild here. They are therefore less reliant on significant winter chill. However, some of such bulbs in several of the milder climates may bloom only once. They lack the winter chill they need to bloom for subsequent springs. Avid garden enthusiasts compensate with refrigeration.

That requires major diligence, though. Most who enjoy gardening do not want to dig and refrigerate dirty spring bulbs. Consequently, most who grow them enjoy them as annuals or disposable perennials. Unfortunately though, spring bulbs do not bloom for very long, and are not inexpensive. That is why they are not as prevalent here as in other climates.

Freesia and narcissus, including daffodil, do not need much chill. They can settle in and bloom for many years after their initial planting. Ranunculus and anemone may not need much chill either, but are less likely to regenerate from year to year. Dutch iris and Dutch crocus are unpredictable. They might become reliably perennial, but may not cooperate.

Tulip and hyacinth may be more disappointing, since they require significant winter chill. If they can not experience such chill naturally from the weather, they require refrigeration. Otherwise, they bloom only once for their primary season, and only after prechilling. Yet, both are among the most popular of spring bulbs. Their blooms are simply too appealing.

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Frosty Weather Can Limit Gardening

Foliar frost damage can be unsightly.

Even here, climate is not perfect. It may sometimes seem to be too warm during summer. However, it might not be consistently warm and humid enough for some tropical species. Winter chill may be inadequate to vernalize some species or certain cultivars of species. However, recently frosty weather has already damaged some vegetation in some areas.

Frost limits what performs well in home gardens in two extremes. Some species prefer a bit more than they experience here. Others prefer less. For example, peony prefers more, while vanilla orchid prefers none. Peony is only marginal where weather is exceptionally frosty by local standards. Vanilla orchid can be offended by minor chill even without frost.

Climates and microclimates limit frost just as frost limits what performs in home gardens. Some coastal climates here only very rarely or perhaps never experience frosty weather. Other climates farther inland or at higher elevations experience frost almost every winter. Within such climates, eaves or canopies of big trees can provide shelter from minor frost.

Vegetation within home gardens should be appropriate to its particular climate. Varieties that are vulnerable to frosty weather are likely safe where frost never occurs. Conversely, they will obviously be susceptible to damage where frost does occur. The best means to avoid such damage is appropriate selection. Climate will not accommodate bad choices.

Gardening could be slightly less interesting without a few bad choices, though. Besides, some of such choices are justifiable with the right perspective. Canna, for example, dies back harmlessly to dormant rhizomes after frosty weather. It wastes no time regenerating as weather warms. Some tropical species may grow in pots to move to shelter from frost.

Tenting can shelter some specimens that are too big to move, or are in the ground. Outer foliage that already succumbed to frosty weather can shelter inner growth. Therefore, if it is not too unsightly, it should remain through winter. Besides, premature pruning is likely to stimulate new growth. Such growth would innately be vulnerable to subsequent frosts.

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Fall Foliage Is Gaining Color

Minor chill can initiate major color.

Fall foliage is underappreciated here. It is not naturally prominent enough to suggest that it should be otherwise. Most native vegetation is evergreen. Most that is deciduous turns simple hues of yellow, without much orange or red. Some just gets shabby and brown as it defoliates with minor chill. Native vegetation does not represent total potential, though.

Contrary to common beliefs, local weather is not too mild for fall foliage to develop color. Only a few locally rare deciduous species need cooler weather for such color. Only a few deciduous species prematurely shed too much to develop their color for fall. Colorful fall foliage really could be more prominent within gardens than it is. It merely is not a priority.

Many home gardens here are within suburban or urban situations. Evergreen vegetation is therefore useful for privacy or to obscure undesirable views. Winter weather is not cold enough for evergreen shade to make it significantly colder. Some believe that deciduous vegetation is messier than evergreen vegetation. Some find it less appealing while bare.

Actually, evergreen foliage is generally more persistently messy than deciduous foliage. Although it sheds less abundantly, it does so more continuously through longer seasons. Some never stops shedding. Ultimately, the quantity of its detritus is at least comparable to that of deciduous foliage. Deciduous foliage sheds more profusely, but does so briefly.

Efficient shedding could be an incentive for deciduous vegetation. Sunnier conditions for winter could be another, whether or not it adds a bit of warmth. The color of fall foliage is obviously worthy of consideration also. Some types are more colorful than others. Some are more reliable than others. Ultimately, there is quite a bit of fall foliage to choose from.

Sweetgum, pistache and flowering pear develop the most exquisitely colorful fall foliage. Their color ranges from bright yellow, through orange, to deep red. Sweetgum is messier than the others, but only because it retains its fall foliage longer. Crape myrtle is smaller, but comparably colorful. Ginkgo is quite reliable for exceptionally brilliant yellow foliage, early in fall.

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Spring Bulbs Benefit From Vernalization

Spring bulbs vernalize with winter chill.

Spring bulbs obviously bloom for spring. Less obviously, they vernalize with winter chill. They are seasonable about now because this is when they should get into their gardens. Many prefer to be interred into their shallow graves by Halloween. Many can wait as late as New Year’s Day. If too much later, some may not experience enough chill to vernalize.

Planting spring bulbs can be ungratifying because there is nothing to see afterward. After all, they are dormant at the time. They lack foliage or any other parts to extend above the surface of the soil. They seem to remain inactive until they bloom as winter succumbs to spring. However, between now and then, they will secretly reset before resuming growth.

Vernalization is how many spring bulbs finish their previous season and begin their next. They know that it is winter after they experience a particular duration of a particular chill. By then, they should have finished all growth of the previous season. Afterwards, all new growth and bloom is for the next season. It is how they know to bloom on time for spring.

Dutch iris, freesia, ranunculus, anemone and common narcissus do not need much chill. Tulip, hyacinth, crocus and a few narcissus and daffodil do. Some bulbs that benefit from it get a prechill treatment before coming to nurseries. Prechilled tulip and hyacinth bulbs are sadly unlikely to bloom after their first year. They prefer more chill than they get here.

Otherwise, many spring bulbs are supposedly reliably perennial. Naturally, actual results may vary. Anemone can survive for many years, but might bloom only rarely. Ranunculus may be less perennial, but may also bloom better while it survives. Dutch iris and crocus are unpredictable. Freesia and simple varieties of narcissus are more reliably perennial.

Technically, some spring bulbs are not bulbs. Ranunculus and freesia, for example, grow from corms. Nonetheless, almost all spring bulbs bloom only once annually. Succession planting can prolong bloom. It provides subsequent phases to begin bloom as preceding phases finish. However, phases of reliably perennial bulbs synchronize after first bloom. Summer bulbs and bulb-like plants are seasonable later.

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See Anemone

Anemone hupehensis

Japanese anemone, Anemone hupehensis, which is now Eriocapitella hupehensis, is one of several species that I had been wanting to grow for a very long time. Like peony, goldenrod, Joe Pye weed, Indian paintbrush, beautyberry and fancy hybrids of clematis, they are prominent features of fancier gardens in other regions. Some of such species do not perform well here. Others are merely unpopular, but might perform well here if they get the chance. I see them all only in pictures, so can not distinguish what their respective situations are. The only anemones that I had ever encountered while young were sea anemones on nearby beaches. In college, I met poppy anemones, which we know merely as anemone, but found that they are not as reliably perennial as they are purported to be. Japanese anemone had been elusive, until I met a very established and perhaps invasive colony of it in an old landscape near Oakland less than fifteen years ago. I figured that if it can be as happy as it was in a relatively coastal climate, it could be happier here with a bit more chill during winter. Until then, I assumed that minimal chill was a limiting factor to their performance here. ‘Honorine Jobert’ seemed to be the epitome of single white Japanese anemone, but I had not seen any white cultivars, even those with double flowers, that were not alluring. Then, I discovered an unidentified cultivar of Japanese anemone on the edge of a rose garden here. It survives as a remnant of a preceding perennial garden, but does not perform well now that redwood roots have become so aggressive. Furthermore, its floral color is unimpressive. It is not white, but is not quite pink either. Heck, it is not even white blushed with pink. I do not know how to describe it. Initially, it seemed to be only slightly pinkish pale gray. Ick! This year, it seems to be slightly more pinkish than it had been, which makes it slightly less disappointing. However, now that I know it is here, I will not try any other Japanese anemone until I at least try to grow this one well. I am confident that if I relocate bits of it to a garden where it does not need to compete with other vegetation, it will bloom with a more appealing shade of pink. I will not mind that it is not white if it does that much. Then, if it can perform well, I will know that I can grow a white cultivar of anemone also. There is no rush though. Although white happens to be my favorite color, and Japanese anemone happens to excel at white, pink can be appealing also. This is my very first Japanese anemone, and regardless of how unimpressive it is now, I am pleased with it.

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Ginger Ail

White butterfly ginger is still green.

At least seven gingers live here. Five are ornamental. Two are culinary. None have yet died back as they should for winter.

Now that it is time to divide them, I do not know what to do with their intact foliage. For this white butterfly ginger from Forest Garden, I divided the rhizomes and installed them into the landscape with their healthy foliage still attached. I do not want to cut it back until it succumbs to frost. I suppose that it can remain as long as it is healthy. It is likely promoting healthier secondary growth. Because none of the gingers are crowded yet, it should not be difficult to selectively groom out older growth as new growth develops. I doubt that older foliage absolutely must be pruned away during winter. If it were that important, the rhizomes would shed it naturally, with or without frost.

This is a mild climate, with very mild frost; but gingers should still die back for winter regardless. Cannas certainly do, even without significant frost. Even some of the banana trees were somewhat unhappy about the chill.

Actually, the banana trees seem to be bothered more by chill than the gingers. Is this normal? Angel’s trumpet, cup of gold vine and blue ginger (which is not related to ginger) also expressed more displeasure than the gingers.

I really should have sheltered some of these species better. Actually, I probably should not be growing so many species that are so sensitive to chill and frost. I will be going to Southern California again in about April, so could bring back even more tropical species. It is a bad habit.

Technically, the average last frost date is about a month and a half from now. Technically, a bit of frost is possible even after that.

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Summer Bulbs Begin In Winter

Summer bulbs bloom after spring bulbs.

Spring bulbs begin to go into the garden during autumn to benefit from the chill of winter. Summer bulbs begin to go into the garden during late winter to avoid the chill of winter. Spring bulbs know to remain dormant through winter. Some summer bulbs do not. If they grow prematurely, they can be vulnerable to cool wintry weather. Late is better than early.

Frost is still possible within some climates. However, summer bulbs are now in season. That is because, like spring bulbs, they disperse roots prior to developing foliage. By the time they extend foliage in a month or so, the weather will not be so cool. Later phases of a few sorts bloom later to prolong bloom for the first season. They synchronize afterward.

That is because they establish themselves within the garden. Once they do, some types of summer bulbs become hardy perennials. Some might try to grow prematurely during subsequent winters. If they incur frost damage as established perennials, they can easily replace the damage. Ornamental gingers and cannas do so regularly in inland climates.

Ornamental gingers and cannas may eventually benefit from division. Even if they do not become too crowded, they can migrate where they are not wanted. Their surplus is easy to relocate or share while dormant for winter. Their foliage becomes shabby or dies back during dormancy anyway. Even if mostly green, its removal stimulates healthy refoliation.

Ornamental gingers and cannas also are oblivious to phasing. Gingers bloom only once for late summer or autumn. Cannas bloom randomly from spring until autumn. Gladiolus bloom only once like gingers, but are more conducive to phasing. Early planting allows early bloom. Late planting delays bloom. Unfortunately, they are much less sustainable.

If summer bulbs do not look like bulbs, it is because few actually are. Most are rhizomes. Dahlias, which, like cannas, bloom from spring until autumn, grow from tuberous roots. As the name implies, tuberous begonias grow from tubers. Crocosmias grow from corms. So do taros, which are large foliar perennials. Gingers and cannas are familiar rhizomes. Although alliums bloom as summer bulbs, they go into the garden along with earlier spring bulbs.

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Proof of Seasons

Daffodil bloom here as if they were in the Pacific Northwest.

Narcissus make me wonder. Both paperwhite and common daffodil, as well as a few fancier daffodil, bloom here as if they were in a climate that is more conducive to such performance. The happiest naturalize and slowly multiply. Not many bulbs do so where winter weather is so mild. That is why I do not bother with tulip or hyacinth, although a few hyacinth have also been performing reliably here for many years.

Peony is very marginal here. I know that they perform inexplicably well for some neighbors, but none have ever done well for me. I really do believe that they prefer more chill than they experience here. Realistically, winter weather is relatively mild here.

Yet, I am not convinced that it is as mild as I have always believed it to be. Some who are unfamiliar with California believe that we experience only two seasons, which are summer, and a few days annually that are not summer. I know better. No one argues that the warm and dry summers here last longer than elsewhere. Prior to summer though, spring is likely comparably to spring within other climates. After summer, autumn, although mild, is cool enough to initiate autumn foliar color. Then, winter is cool. Really, it is cool enough for deciduous species to defoliate, and for mild frost. It may not get as cold as it does in other climates, but how cold does it need to be to qualify as winter?

I am satisfied with the winters here. I can grow all of the deciduous fruit trees that I want to grow. This is one of the best climates in the World for roses. These daffodils seem to be quite satisfied as well. In fact, they sometimes stay dormant later here than in climates with cooler winters!