From Phenology to ‘Silver Falls’

According to Webster’s dictionary, phenology is the study of recurring biological phenomena as harbingers of seasonal change.
For example, if you live in a northern state, phenologists would say that birds flying south is a sign that winter is approaching. If you live in an eastern state, blooming lilac bushes are a phenological sign that frosty nights are over and spring is on its way.
And if you live in Southern California, flowering jacaranda trees portend the arrival of summer heat even if it’s still April or May.
In their native forests of Brazil, Argentina and Peru, jacarandas are known to flower with special intensity following prolonged dry spells.
Exceptional flowering in any plant may be a response to stress. The plant “thinks” its life could be in danger and puts out an abundance of flowers to ensure that, prior to its possible demise, sexual reproduction occurs. This would explain the current heavy flowering of our jacarandas, considering the below average amount of rain we received this winter. Normally, 15 inches of rain falls during a Los Angeles winter but this year we received less than 9 inches.
The full glory of jacaranda trees may be best appreciated along Stansbury Avenue in Sherman Oaks. You wonder why more Valley parkways are not planted with these beauties.
True, jacarandas can grow to more than 60 feet and their brittle branches are prone to breakage. And jacaranda roots grow into water lines and push up sidewalks.
Yet jacarandas, like California sycamores and coast live oaks, are worth the maintenance they require because of the elegance and opulence they bring to any neighborhood. I know, I know. In an era of scarce city funds, smaller trees such as crape myrtles are invariably selected when planting the urban forest. But still, the value of larger trees in parkways is inestimable.
Strangely enough, I was once called upon to prune jacaranda flower buds. I had never heard of someone pruning flower buds, but the voice on the other end of the line was adamant. How much would I charge to cut all the flower buds off a large jacaranda tree, the voice wanted to know.
It seems hard to believe, but some people hate jacaranda trees because of the sticky flowers they produce. It’s almost like hating the sun because it can give you sunburn. Have these people never stepped back to marvel at a jacaranda in full bloom? Certain jacaranda detractors will concede there is some beauty to behold in a blooming jacaranda tree, but such beauty cannot, according to them, compensate for the mess created by the flowers.
It’s true that jacaranda flowers, if not removed soon after falling, could stain the paint on your car and, since they stick to the soles of your shoes, may also end up on the living room carpet. But these inconveniences seem to be a small price to pay for the miraculous floral display provided by jacarandas this time of year.
In Los Angeles, no tree is more breathtaking than a jacaranda in full bloom. Its nickname of “blue haze tree” is well chosen. On a mature tree, an ethereal lavender-blue cloud engulfs its majestic canopy, a good 50 feet high and nearly as wide.
Alkalinity explained
It is time to clean out the fireplace. Are wood ashes beneficial to the soil in my garden?
– Marlene de Valera
Simi Valley
Wood ashes are not recommended for Southern California garden soil. The reason has to do with the alkalinity of wood ashes, which leads to an increase in soil pH. Our soil pH is nearly always on the alkaline side so making it more alkaline would be detrimental to plant growth.
Most plants prefer a slightly acidic pH of around 6.5, while our soil has a pH that is consistently greater than 7. While it is true that California native plants typically prefer an alkaline soil pH, I would not recommend raising soil pH when planting them either. California natives prefer native soil and its pH should not be altered.
Keep in mind, also, that the pH scale is logarithmic. This means that a pH of 8 is 10 times more alkaline than a neutral pH of 7, and a pH of 9 is 100 times more alkaline than a pH of 7. Thus, an increase in soil pH could have drastic effects.
By contrast, in wetter climates, where heavy rainfall leaches alkaline elements such as calcium out of the soil, creating a detrimentally acidic soil pH application of wood ashes can be highly beneficial.
Rarities in Calabasas
If you visit Sperling Nursery in Calabasas, you may encounter plants that you have never seen before.
Calabasas is in a transition zone, bridging the San Fernando and Conejo valleys, so it benefits from a moderating ocean influence that more-landlocked Valley residents can only dream about.
In the nursery’s parking lot, there is a glorious orange clock vine (Thunbergia gregorii) that appears to have been there for years. In many parts of the Valley, cold winter nights are likely to kill this plant, so that it will bloom gloriously for one season only.
Australian woollybushes and jugflowers, belonging to the genus Adenanthos, are on display at Sperling Nursery. These plants are impossible to resist. Coastal jugflower (Adenanthos cuneatus ‘Coral Drift’) has uniquely shaped scarlet-tipped foliage and Albany woollybush (Adenanthos x cunninghamii) has a low-growing, lacy, yet furry presence.
Speaking of furry, I was stopped in my tracks by an oriental spruce (Picea orientalis ‘Atrovirens’). This tree’s foliage is a collection of tactile green caterpillars. It would be a comforting presence growing in a container on a shady patio, although it would probably have trouble accepting alkaline Valley soil, and dry summer heat, if it were planted in a sunny garden spot.
If you are on the lookout for distinctive flowering vines, Sperling has a wonderful collection of passionflowers (Passiflora species) and Clematis, the latter in pink, pale blue and royal purple varieties. There is also a stunning giant potato creeper vine (Solanum wendlandii) available.
Tip of the week
At Sperling Nursery, the many mixed container and hanging basket plantings on display are a learning experience as far as choosing combinations of plants for pots or flower beds. Above all, I was impressed with a lemon yellow, low-growing zinnia (Zinnia angustifolia), left, that seemed to combine well with everything. There was also a dazzling hanging basket that featured a dusky red Dipladenia contrasting with a rich botanical tapestry known as Dichondra ‘Silver Falls,’ right.

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