Hydrangeas Grow Well Under Walnut Trees

hydrangea with bacopa

hydrangea with bacopa

Less than a century ago, thousands of acres of walnut orchards thrived in what would become the Los Angeles megalopolis.
Today you can find the remnants of these orchards in equally spaced walnut trees, one per front yard, in residential neighborhoods from Woodland Hills to Encino to Arcadia.
While soliciting your advice on how to grow hydrangeas, I received an e-mail from Claire Martin, who lives in Winnetka.
“Not to boast … OK, to boast,” she wrote, “I have the most brilliant-looking hydrangea around. In fact, I have not seen one nicer than mine, or one displaying more flowers, in the entire Valley. It lives under the shade of a magnificent walnut tree in my front yard, and in circumference is about 15 to 20 feet. It is in full bloom right now, and people stop to ask me how I manage to grow this plant. Care to come see it?”
Always on the lookout for horticultural wonders, I could not resist such an invitation. Martin’s hydrangea was just as she described it, if not more so. In fact, the diameter of her single plant was around 12 feet, with the circumference more than 30 feet around.
A strange place for plants
I was surprised to see such abundant growth under a walnut tree, due to its allelopathic character. Allelopathy refers to the production of toxic substances by certain plants — in their leaves, wood, bark, and roots — that discourage other plants from growing in their vicinity. The allelopathic substance in walnuts is known as juglone. Yet, hydrangea makes the list of plants resistant to juglone and, judging from the appearance of several scores of its pink mophead flowers, it is as though something in the walnut’s chemistry actually stimulated this hydrangea’s growth.
Martin never fertilizes her hydrangea and waters it daily this time of year.
“During the summer, I water it through drip irrigation tubing 15 minutes a day,” she explained. “Other than that, I do nothing except talk to it. And it grows. It was killed back by the freeze last winter, but you would never know that from looking at it now.”
Martin has several other plants that grow with a minimum of care. She says she has a “Darwin garden” since only the fittest plants — those not needing much attention — survive. She has a rangy Texas ranger (Leucophyllum frutescens) covered with bell-shaped mauve-pink flowers that show up well against silver-gray foliage. Catmint (Nepeta faassenii) is a spreading ground cover plastered with violet-blue flowers and attractive heart-shaped foliage. Neighborhood cats are frequently found lounging in it.
In a sun-splashed planter, Martin has allowed a crop of Matilija poppies (Romneya coulteri) to spread. Sometimes called fried-egg plants on account of their flowers — large yellow centers surrounded by crepe white petals — these California native poppies can grow without any summer water, although they will spread that much faster with regular irrigation.
Fenced in
If you are looking for a natural fence, consider the butterfly rose (Rosa mutabilis). On one side of my front yard, three of these rose bushes have grown into a 6-foot-tall thicket topped with simple, six-petaled flowers, as opposed to the more familiar multi-layered hybrid roses. What these roses lack in layers of petals they make up for in their color, which changes from yellow to orange to pink to crimson in the course of their bloom. Hundreds of roses will cover these three plants at any given moment, since they bloom on and off throughout the year.
Benefits of a freeze
I cannot help thinking that the freeze we had in January, at least where plants survived, was beneficial. The vigor of plants this summer surpasses what they usually show. Pests seem to be less of a problem than normal, and perennials — from hydrangeas to roses — are more floriferous than usual. It could be that the deciduous (or at least semi-deciduous) growth habit of roses and hydrangeas contributes to their robustness following a winter freeze, the same way that deciduous fruit trees — apples, plums, and apricots, for example — may produce heavier crops following a colder than average winter.

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