Mistletoe is a parasite, tapping its host trees for water and nutrients. Being a green plant, however, it also produces its own food through photosynthesis.




Photograph by Shari Kaplan







Sensitive plants require winter frost protection

By Tony Tomeo

The climate in the Santa Clara Valley must be the best in the world. Summers are relatively mild with minimal humidity and autumns are cool enough to stimulate foliar color among several species. After that, winter does not become too uncomfortably cold. Only a few species require protection from frost and only for a few days during winter. In fact, it is already the day after Christmas, but there have only been a few nights of mild frost.

In other climates, many species easily grown here--including citrus and most palms--either cannot be grown, or must be brought inside for winter. My father, who lives on the Olympic Peninsula in Washington, must even bring much of his coniferous bonsai stock into a greenhouse to prevent the soil in the pots from freezing. Unlike the inexpensive greenhouses popular here, a more substantial greenhouse that will support the weight of snow is necessary. Fortunately, he can afford it because he did not send me the new Buick I wanted for Christmas.

Frost protection is much simpler here and only necessary for a few species. Many sensitive species can be successfully grown without protection if strategically located in protected areas of the garden, such as under eaves or larger trees, if sun exposure is adequate. Under the eaves of heated homes, radiant heat from an exterior wall will also be appreciated. Exposed walls that face south are warmer during the day and consequently radiate more warmth at night. Incidentally, such walls are good locations for species that require protection but enjoy warmth in summer, such as bougainvillea and hibiscus.

The most sensitive species that can be damaged by even mild frost should be grown in containers if practical. They can then be relocated during frosts or for the entire season. Larger items are obviously more easily relocated for the entire season than every time they are threatened by frost. Porches, lanais, carports and covered patios are actually better protection than larger shade trees. Those of us with nothing to park in a garage may use the space to store plant specimens if sun exposure through windows is adequate.

If "tenting" specimens installed in exposed areas, the covering material should not touch foliar surfaces. Otherwise, moisture that condenses on the cover may freeze on the foliage and damage it worse than if it were left exposed. Coverings should be removed during the day.

One of my neighbors in San Luis Obispo placed either inner tubes or bleach bottles painted black and filled with water around sensitive specimens so they would be under the tents at night. The black rubber or paint would collect and transfer solar warmth to the water from which warmth radiated at night. It was unsightly and I never quite figured out how the water got inside the inner tubes, but I don't remember seeing any frost damage in that garden. However, I would think that the water would be frozen by morning before dawn, when warmth is most critically needed.

Frost-sensitive species should not be pruned too late in summer or autumn because the resulting new growth is most sensitive. If a specimen becomes damaged by frost, it should not be immediately pruned. Damaged parts may be unsightly, but they insulate inner growth that may not have been damaged.

Plant of the Week: Mistletoe

Mistletoe, Phoradendron villosum, is not a species enjoyed by many garden enthusiasts--not because it is rare, but because it can be so damaging to desirable trees. This parasite of western trees is commonly displayed as cut foliage during the holidays because it resembles European mistletoe, which for centuries has represented fertility because it remains green while the host tree is dormant and bare.

The inconspicuous flowers, which incidentally are the state flower of Oklahoma, produce toxic (to humans) white berries that are eaten by birds, which deliver seeds to other trees. Mature plants may be several feet wide with yellowish green foliage. Infestations are often controlled by removal of all foliage, but mistletoe may emerge again from root-like structures known as haustoria that have become established below the cambium of branches. Consequently, eradication may require the removal of all infested branches.

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Horticulturist Tony Tomeo can be contacted at 408.358.2574 or at LGHORTICULTURE@aol.com.

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