Mild Weather Is Still Problematic

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Minimal frost delayed certain spring blooms.

It is amazing that so many orchards are so productive in California, and that so many similar orchards had formerly been productive in the urban areas in which so many of us now live. Nowadays, it takes so much work to care for just a few fruit trees in home gardens. Horticulture is not what it used to be.

Diseases and pests get transmitted all over the world at a rate unlike at any other time in history. It is just too easy to buy and sell infected plants online, and get them delivered without adequate inspection. Many varieties of plants that are so easily imported may not perform as reliably as the more traditional varieties.

Modern landscaping does not make fruit production any easier. Most deciduous fruit trees do not get pruned adequately or properly. Many get too much water. Almost all must live in crowded landscape conditions where diseases and pest proliferate. Sanitation (removal of infected plant parts) is rarely as efficient as it should be.

Then there is all this crazy weather! First, the winter does not get as cool as it should. Then, it does not get warm enough in spring. It is all so difficult to keep track of. Many plants do not know how to respond. Those that stay dormant through cool weather got an early start. Those that like warmth in spring started late.

The unfortunate deciduous fruit trees that need both a good chill through winter and nice warm spring weather are really confused. Early blooms were ruined by brief late frosts or brief rain showers. Some delayed blooms were not synchronized with pollinators. Some of the minimal fruit is developing slowly.

Even the fruitless or ‘flowering’ relatives of the deciduous fruit trees are annoyed by the weather. Many flowering cherry trees that should have bloomed profusely prior to foliation delayed bloom until lower foliage started to appear. However, both bloom and foliation are so slow and sporadic that upper stems stayed bare quite late.

Flowering crabapple trees, which generally bloom after flowering cherries, actually bloomed more reliably, and were not delayed as much. Hopefully, fruiting apple and pear trees, although late, will be more productive than so many of the cherry, apricot, plum, peach and nectarine trees will be this year.

Frost Is Now Old News

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Minor frost can cause major damage.

Frost was something of a nonissue for some of us this winter. For those of us in milder climates, in rarely is. Those who limit selection of what grows in their gardens to species that are resilient to frost need not be concerned with it. Those of us who enjoy gardening a bit too much are more likely to grow a few marginal species that would prefer to be somewhere with milder winter weather.

Protection from frost might have been a concern prior to the onset of cold weather. Then, there was more concern for the few plants that might have been damaged by frost. Grooming and pruning of damaged foliage and stems needed to be delayed until after the threat of subsequent frost. Now that it is so late in the season, subsequent frost is very unlikely. It is safe to clean up any mess.

Pruning and grooming of foliage and stems that were damaged by frost is delayed for two main reasons. Firstly, the damaged material, although unsightly, helps insulate undamaged foliage and stems below it from subsequent frost. Secondly, premature removal of damaged material stimulates premature development of new foliage and stems that are more sensitive to subsequent frost.

Not only is it now safe to prune and groom frost damaged plants, but such procedures should not be delayed while affected plants recover. The same frost damaged material that provided a bit of protective insulation earlier would now interfere with the healthy development of new stems and foliage. Pruning can now promote new growth that was preferably delayed through colder weather.

Because the weather has been so pleasantly mild for quite a while already, new growth may already be developing among some frost damaged plants. Damaged material should be removed as carefully as possible to limit damage to such new growth. Many perennials that were not damaged this year might be pruned as if they were, to remove tired old growth, and promote new growth.

Many of the dormant spores of fungal and bacterial pathogens that overwinter in old foliage will be removed as such foliage gets groomed away.

Some Annuals Are Not Annual

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Some summer annuals can survive winter.

So many annuals are actually perennials. They just get dug and replaced because they are not pretty enough during their off season. For warm season annuals, winter is the off season. For cool season annuals, summer is the off season. However, if left alone, many annuals that are actually perennials go dormant so that they can survive through their off season to regenerate and perform again for another season, or several seasons

Cyclamen and various primroses are cool season annuals that are in season now. Cyclamen will go dormant and defoliate as the weather gets warm in summer. Primroses do not defoliate, but get rather runty through warm weather. If planted with other light duty warm season perennials that take over for them, no one notices. For example, primroses are colorful enough now to distract from tired fleabane. By the time primroses fade, the fleabane takes over.

Chrysanthemums are among the flashiest of perennial annuals, but also have a short season. They typically get planted while blooming in autumn, but finish their bloom cycle before winter. After all the rain and cool weather . . . and then a bit of warm weather, some are already dying back to the ground; but closer examination might reveal new growth already emerging from the roots!

Nasturtiums can obscure regenerating chrysanthemums nicely. If the frost sets them back, they recovery quickly. They will bloom more colorfully by spring, and continue until summer gets too warm. By that time, the chrysanthemums should be filling out nicely to bloom by autumn. As the chrysanthemums finish, the nasturtiums will have sown their seeds, so that the process can start over again. Neither chrysanthemum nor nasturtium need to be removed while out of season. They only need to be pruned back and groomed accordingly.

Coleus, impatiens, fibrous begonias and maybe even polka dot plant that were only moderately damaged by frost might be salvageable if they can stay put long enough. That is the advantage of growing them in pots with other small perennials that will cover for them when they die back or need to be pruned back.

Frost Is Just Too Cool

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Frost makes tender foliage ugly fast.

Is it too late to warn about frost? After all the rain, the recent and sudden cold weather was quite a surprise. Fortunately, these recent frosts were relatively mild. This sort of weather is probably just enough to start to satisfy plants that require chilling through winter without causing too much damage to too many sensitive plants. So far, only the most sensitive plants, like angels’ trumpet, canna and left-out houseplants show symptoms of frost damage. (Cannas should get cut to the ground at the end of winter anyway.)

Doing without all frost sensitive plants would be too limiting. Lemon, avocado, bougainvillea, fuchsia and Australian tree fern would be off limits. Such plants are worth growing, as long as we understand the potential for occasional frost damage. Those that are too big to protect may sometimes need to get pruned for removal of stems that get killed by frost. In milder climates, such damage will be very rare. In cooler spots, damage is more common, and may involve a few tougher plants, like jacaranda.

Smaller plants that are sensitive to frost, such as jade plant, angel wing begonia and the various pelargoniums, can be grown in containers so that they can be moved to sheltered spots before the weather gets too cold for them. The most sensitive sorts need to be moved under a porch roof or eave, or maybe into a garage. More resilient plants may be safe under overhanging trees or against a wall. South or west facing stucco walls radiate a slight bit of warmth at night.

Frost sensitive plants that get too big for containers should be planted in sheltered spots, like below eaves or larger trees. If a severe frost is predicted, young plants can be protected by burlap, paper, trash bags or any convenient sheeting suspended above by stakes. Foliage that touches the sheeting may get frozen, but foliage within should be fine.

Foliage and stems that get damaged by frost should not necessarily get pruned away immediately. Although unsightly, the dead foliage insulates damaged stems below from subsequent frost. Besides, premature pruning can stimulate new growth, which is more sensitive to subsequent frost.

Some Plants Need To Chill

41210thumbIt is easy to snivel about the weather when it gets uncomfortable for us. The rain gets too wet. The temperature gets too cool. Even here on the west coast, without the cold of Minnesota, the heat of Arizona, the humidity of Louisiana or the rain of the west coast of Washington, we tend to think about weather by limited human standards. What we fail to consider is that many other organisms rely on a variety of weather conditions for their survival.

Deciduous plants make it obvious that they know how to deal with cool winter weather. What is not so obvious that that many deciduous plants actually need specific wintry conditions to be convinced that it really is winter. If the weather does not get cool enough, or stay cool long enough, some plants do not go dormant long enough to get the rest that they need in order to perform adequately the following spring and summer.

For example, the reason that only a few of the many different varieties of apple can be grown locally is that most have chill requirements that exceed what they get here. A chill requirement is a specific duration of cool winter weather. Only a minority of all varieties were bred for their minimal chill requirements, so that they will produce reliably even where winters are innately mild.

Besides chill requirements, some seeds like to be soaked in moist soil before they germinate the following spring. This lets them know that it is raining, like it typically does in winter. Pecans, for example, can be soaked for a while inside before sowing, bur really prefer to be out in the garden through winter, where they can tell than rain water is actually flowing past them through the soil, and the microorganisms in the soil help to break down their shells.

It is all about timing. Chill requirements get apple trees to bloom in spring, only after they were convinced that it was already winter. If they were not so specific, they might bloom after a brief cool spell in autumn, leaving their blossoms or developing fruit vulnerable to later frost. Pecans germinate and grow only after the danger of frost, but before the weather gets too dry. If they start too early, they may not survive frost. If they start too late, they may desiccate through summer.

Way Beyond Last Frost Date

90410thumbScheduling of gardening chores is as important now as it ever was. We plant warm season vegetables and annuals in time for spring and summer. We plant cool season vegetables and annuals for autumn and winter. We pick flowers as they bloom. We harvest fruits and vegetables as they ripen. We watch the seasons change on our calendars, as well as in the locally specific weather.

Yet, the one scheduling tool that we do not hear as much about as we did when agriculture was more common in the region is the ‘last frost date’. It refers to the average date of the last potentially damaging frost for a specific region. The last of such frosts might actually be earlier or later, but the last frost date remains a standardized time to plan particular procedures and planting around.

There are likely a few reasons why we do not talk about the last frost date much. The most relevant reason is likely the timing. Around here, the last frost date is sometime in January. It is earlier in some spots, and later in others, but it is sometime between January 1 and 30. It is simply too early to limit much of what we do in the garden in early spring, and is irrelevant to most winter chores.

It might seem to be just as irrelevant now, since the last frost was so long ago. Seed for warm season vegetables and annuals is sown as the weather gets warmer only because it would grow too slowly while the weather is too cool in winter, not because of a threat of frost. There really is quite a bit of time between the last frost and warm spring weather, while the weather is still rather cool.

However, pruning of plants that were damaged by frost should have been delayed at least until after the last frost date, and perhaps as late as spring. Although unsightly, damaged growth shelters inner growth from subsequent frost. Besides, premature pruning stimulates new growth that is more sensitive to subsequent frost. Most of such pruning is delayed until just after the last frost date.

If delayed longer, fresh new growth will show how far back damaged stems must get pruned.

Get Perennials Ready For Winter

81212thumbDilemmas are common in gardening. Should summer vegetables that are still producing be removed so that winter vegetables can get started on time? What about replacing summer annuals that are still blooming with winter annuals, and then replacing winter annuals with summer annuals half a year later? Should tender perennials be regarded as annuals, or get a second chance?

Right now, some perennials are looking tired. Many will be going dormant for winter. Many do not get much down time, and will start to develop new growth faster than old growth deteriorates. Not many make their intentions obvious. Deciding how to work with them can be confusing at times. It might take a few years and a few mistakes to get familiar with the habits and lifestyles of some.

If cut back too early, hardy zonal geraniums will not regenerate much until the weather gets warmer at the end of winter. In the interim, they are more likely to be killed by frost without the protection provided by old growth However, some varieties start to grow in winter. If not cut back soon enough, new growth mingles with old, so that they are difficult to separate when they do get cut back.

It is best to observe what hardy geraniums are up to before deciding on when to prune. If they start to develop vigorous new growth down near the ground, the old growth should probably be cut down as far as the new growth. It is likely better to take a chance that they might be damaged by frost. Those that do not start to grow right away can enjoy the insulation of old foliage for a while.

Thoroughly deciduous perennials, like deciduous daylilies, dahlias and some ferns, can be groomed of their deteriorated old growth without risk that they will start to regenerate new growth prematurely. However, cutting back some specie of salvia might actually stimulate development of exposed and frost sensitive new growth. Perennials that get damaged by frost later In winter should not be groomed of damaged growth right away. The damaged material provides a bit of insulation for lower growth, particularly if new growth was stimulated by the damage.

Being Cool Might Be Overrated

31218thumbThis really is the best climate for gardening. Even though summers are mild, there are not many plants that want for more warmth. Even though winters are mild, it gets just cool enough for many plants that require winter chilling. Yet, there are a few plants, particularly plants from tropical climates, that can be damaged by frost. The best way to protect such plants from frost is to not grow them.

Of course, this oversimplified technique would prevent the cultivation of familiar plants like banana, angel wing begonia and angel’s trumpet. In cooler regions, it might involve bougainvillea, philodendron and some types of citrus. Most of us would prefer to take some degree of risk to grow marginal plants. Some may get damaged by frost and then recover. Others may be killed by frost.

Potted plants can be moved to sheltered spots when threatened by frost. Some can be brought into the home or garage temporarily. For some, the simple shelter of a porch or a dense evergreen tree might be sufficient. Bougainvillea and other plants that do not like to be potted might prefer to be planted under the eaves against a warm south-facing wall. A bit of warmth radiates from walls at night.

During the coldest nights, some of the most sensitive plants that can not be moved to shelter may need shelter brought to them. Burlap, plastic, paper or any sort of sheeting that can be temporarily suspended on stakes above the foliage should be sufficient. Leaves that touch the sheeting can potentially get frozen. The sheeting should be removed during the day so that it does not get too warm in the sunlight.

Foliage that does get damaged by frost should not be pruned away immediately. It may be unsightly, but if left for later, it helps to insulate inner foliage and stems from subsequent damage from later frost. Besides, immediate pruning stimulates new growth that will be even more sensitive to frost than was the foliage and stems that had already been damaged.

Frost

P81125We 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.

Frost Is History For Now

80328thumbThere is no doubt that frost will return next autumn. It does that every year. Right now, we are more concerned that is should not return prior to that. It is now safe to plant plants that are sensitive to frost. Even if the weather were to somehow get cold enough to necessitate protection of frost sensitive plants, it will not be severely cold, and it will not last long. It is best to start now than to delay.

It is also safe to prune away foliage and stems that were damaged by frost through winter. It was best to leave it in place through winter, both to provide a bit of insulation for undamaged stems below, and to not promote new growth. Pruning it away allows warming sunlight to the undamaged stems, and stimulates generation of new growth. A bit of new growth might already be apparent.

Many leafy perennials can be cut to the ground, or at least just above their rhizomes. The tall vertical canes of cannas can be cut back to the low horizontal rhizomes that creep along the ground. The canes are not really stems anyway, but are merely upright foliar shoots. Any shorter new shoots that are beginning to develop can remain, even if a few outer leaves happen to be damaged.

Zonal geraniums can likewise be pruned almost to the ground, leaving only stubs of lower stems, even if only upper and outer foliage was damaged by frost. Although they do not need to be cut back so severely, they respond to such pruning splendidly, with vigorous new stems and foliage. The fungal foliar disease known as ‘rust’ overwinters in old leaves that get removed in the process.

Lemons, limes and any other citrus that were damaged by frost only need to have their damaged stems removed as far back as viable growth, where new buds might already be visible. However, if more pruning is necessary, this would be a good time to do it. Major pruning should not be done later in summer because the sensitive bark of inner stems can be scalded by sudden exposure to too much sunlight. Small trees that are sensitive to frost become more resilient as the grow larger.