California buckeye, Aesculus californica, is an enigma. How does it survive while defoliated for so much of the year? Not all are so mysterious. Those that live in sheltered or forested situations behave like normal deciduous trees, by defoliating in autumn, and refoliating in spring, after a brief winter dormancy. Those that are more exposed in warm and windy situations make us wonder.
After their brief winter dormancy, exposed California buckeye trees refoliate early in spring, as they should. Then, only a few month later, they defoliate through the warmest and most arid part of summer, which might be a few months long! As the weather cools and the rain starts, they refoliate briefly for autumn, only to defoliate in time for their winter dormancy. They are ‘twice deciduous’.
How do they photosynthesize enough to survive? It seems like they would consume more resources in this process that they could generate. They obviously know what they are doing, since they survive quite nicely in the wild. Furthermore, they are not the only species that can do this. Sycamores sometimes do it if the weather is just so, or if they get infested with anthracnose too severely.
Most deciduous plants defoliate only in winter because that is the worst time to try to photosynthesize. There is less sunlight available while the days are shorter, and the weather is cloudier. Frost, wind and snow would cause much more damage if deciduous plants retained their foliage. Defoliation is how they accommodate the weather. It is no different for plants that defoliate in summer.
Much of California is within chaparral or even desert climates. Native plants, as well as plants that are from similar climates, know how to live here. If they happen to be in a hot and dry situation, some may go dormant until the weather improves, even if they do not go dormant through the mild winters. This is why wild arums and some unwatered acanthus have died back to the ground, and why naked lady amaryllis will remain naked until the first rains in autumn.
Are warm season annuals really the most colorful flowers for summer? Perhaps. They have their limits though. They are also very demanding. They need to be watered very regularly, and should probably be fertilized too. Many need to be deadheaded frequently. After all that, they are only temporary, and will get replaced with cool season annuals in autumn. Perennials are more practical.
Lily-of-the-Nile is likely the most common and most familiar of blooming summer perennials. It is a shame that it blooms only once. Bloom is usually in time for the Fourth of July, and lasts a good long time, but is already fading. Deadheading as the blue or white color is eventually exhausted will not promote subsequent bloom, but will keep the evergreen foliage looking tidy until next year.
Daylily might be the second most popular of summer perennials. Some of the older types bloom only once like lily-of-the-Nile, but various cultivars bloom at various times to prolong the season if a few are grown together in the same garden. The most popular modern cultivars probably bloomed earlier, and will bloom again, perhaps with little time in between. The color range is extensive.
Penstemon are not committed to their natural schedule of blooming in late spring and again in autumn. A good pruning at the end of winter eliminates tired old foliage, and enhances and delays bloom until summer, without compromising the later autumn bloom. Like daylily, a few different varieties of penstemon in the same garden prolong bloom, which can be white, pink, red or purple.
Salvias are a big group of summer perennials that really should be more popular than they are. Some are native. Others are from other chaparral climates. Naturally, they are right at home here. Many bloom about now, and some will bloom again in autumn if deadheaded or pruned back. What they lack in flashy color, they compensate for in resiliency and reliability. They really are tough.
This is by no means a complete list of summer perennials. It does not even include the perennial daisies such as coneflower, black-eyed Susan and gaillardia.
Does the heat seem to have come on suddenly this year? There was all that rain through winter, then a quick but delightful spring, and now it is suddenly over a hundred degrees in some places! What happened?! There is certainly nothing abnormal about such warmth in the middle of June. It just comes as a surprise when it arrives so suddenly after such pleasantly mild spring weather.
At least warm weather here is not as dreadful as it is in other climates. It cools down a bit overnight. Humidity is typically (although not always) low. There is typically at least a bit of breeze by late afternoon, just after the worst of the warmth. We need not contend with the sort of dankly humid heat, that lasts all day and into the night without even a slight breeze, that so much of America gets.
Of course, that is no consolation now. By our standards, it is hot. Gardening is no fun, and some of it gets neglected. We become more aware of where shade trees should have been planted. We might also notice wilted or pallid plants that are not getting enough water. Pruning that was delayed while new spring growth matured may need to be delayed a bit longer, until the weather cools.
Unfortunately, the minimal humidity and occasional breezes that make the weather more comfortable for us make it more uncomfortable for the plants in the garden. Plants can realistically tolerate more heat than we can, but prefer it to be in conjunction with humidity. Otherwise, they can lose too much moisture to evapotransipiration (evaporation from foliar surfaces), and wilt or desiccate.
Automated irrigation obviously needs to be adjusted accordingly. Potted plants need more of an increase than those in the ground. Those that are overgrown, in hanging pots, or exposed to the typical evening breezes will be the most consumptive. It is not always easy to know how much they need, but one can be certain that if they are wilting, they need more than they have been getting.
Pots exposed to sunlight can get uncomfortably warm. If cascading or bushy growth does not shade the south sides, smaller potted plants can.
It makes sense for flowers to bloom in spring. Winter is too cool, windy and damp for both flowers and the insects that pollinate many of them. By summer, successfully pollinated flowers have faded, are busy making seed to disperse in autumn. Some plants produce fruit to get birds and other animals to disperse their seed. There are certain advantages to blooming early in the spring.
Native plants that are endemic to chaparral climates are quicker with bloom, so that they finish before the air gets too arid. Desert plants might bloom for less than a week. Some tropical plants might bloom whenever they want to because they do not understand the concept of seasons, but they are not the prominent plants in our gardens. Therefore, flowers get scarce this time of year.
Besides the few perennials and annuals that bloom as long as the weather stays warm, there are not many plants that bloom reliably so late in summer. Belladonna lily, which is also known as naked lady, might be one of the flashiest, as its bright pink flowers bloom on top of bare stalks before the low basal foliage develops. It was actually dormant through the warmest part of summer.
Billowy and bold pampas grass flowers bloom this time of year, but are uncommon. The boldest type of pampas grass is too big and difficult to manage for home gardens. The smaller type has dingy tan flowers, and is so invasive and weedy that it is unavailable in nurseries. Those of us who have it in our gardens did not plant it. Other grasses with nice late flowers are not very colorful.
Russian sage has become one of the more popular late blooming perennials. More traditional Japanese anemone, goldenrod, lion’s tail and showy stonecrop all seem to have lost popularity over the years. Mexican blue sage should bloom best late in summer, but often finishes sooner than expected. Yarrow often blooms later than expected, until summer ends. Marigold, blanket flower and some sunflowers bloom until frost. Chrysanthemums, whether grown as annuals or perennials, are just beginning late in summer.