September 24, 2021

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Late summer bloom until frost | Tony Tomeo | Home & Garden

Seasonal changes keep gardening interesting. Like colors of a rainbow, seasons are not as distinct as their dates on a calendar imply. Each evolves into the next. Spring evolves into summer. Late summer is presently evolving into autumn. It happens like red evolves into orange on a rainbow. It is amazing that plants can monitor the changes so precisely.

Even if plants could monitor calendars, they would not. They are too busy monitoring the daily duration of sunlight. That is how they identify primary seasonal changes. Of course, they monitor the weather also. That is how they know more precisely when to react to the seasonal change. Plants are aware that it is now late summer, and they know what to do.

Most but not all plants bloom during spring or summer, so finish by late summer. By now, they prefer to prioritize seed production. Some continue to produce fruit to entice animals who eat it and disperse its seed within. However, some plants prefer to bloom late. Some bloom during autumn or winter. Some are so late that they are early during the next year.

Therefore, there is more to provide floral color through late summer and into autumn than cool season annuals and late blooming perennials. Butterfly bush, plumbago, bee balm, lion’s tail, Saint John’s wort and various salvia are now blooming for late summer. Some might continue into autumn. Oleander and euryops might bloom sporadically until winter.

Strangely, some flowers that bloom for late summer or autumn are from tropical climates. Because equatorial or tropical climates are not as cool during winter, or may lack winter, shortening days are not such a deterrent to bloom. However, many tropical plants bloom sporadically, rather than profusely within a particular season, and may be unpredictable.

Princess flower, mandevilla, hibiscus and angel’s trumpet may bloom at any time prior to winter chill, but may not. Those that do so may not repeat the process annually. Fuchsias are a bit more reliable for late bloom with flowers that are generally more interesting than colorful. Blue hibiscus looks more tropical than it is, with potential for late summer bloom.

highlight: Saint John’s wort

Although it shares the same common name, Hypericum beanii is not the same sprawling Saint John’s wort that is now so aggressively naturalized within some local ecosystems. It is shrubbier and much more docile. Mature specimens get no more than three feet high and wide. It should be evergreen here, but can get sparse through cooler winter weather.

Bloom begins in the middle of summer and continues at least to early autumn. Cheerfully bright yellow flowers are two inches wide, with five rounded petals around fuzzy centers. The light green and oblong leaves are about two inches long. Stems are rather wiry, and can eventually get shabby. Coppicing as winter ends stimulates fresher vigorous growth.

Saint John’s wort prefers sunny and warm exposure. It is otherwise not very demanding. Regular watering enhances bloom. Yet, established plants can survive without watering. Where coppicing (cutting back to the ground) in late winter is not a problem, Saint John’s wort performs well as a low hedge, or unshorn border. Frequent shearing inhibits bloom. Rust is a potentially bothersome fungal disease.