– Barbara Mah
A: Most plants are happiest with a slightly acid pH of around 6.5, including just about everything you would grow in a vegetable garden. This is explained by the tropical origins of plants. In the tropics, the pH is acidic since the heavy rains wash away those minerals – containing calcium and magnesium – that make a soil alkaline. Compost also has a slightly acidic pH, a fact that encourages its use where soil is alkaline.
A short chemistry lesson is needed here: Soil with a pH of 7 is considered neutral; soil with a pH higher than 7 is termed basic or alkaline; a pH lower than 7 is considered acidic.
In the Valley and, for that matter, throughout California and the West, soil pH is usually in the alkaline range. This is due to our low rainfall and the presence of calcium and magnesium compounds, which often keep the pH considerably higher than 7.
Where rainfall is heavier, as in the Northwest, Northeast and Southeast parts of the U.S., pH tends to be in the acid range. In fact, you can generally tell what kind of pH a plant prefers by its habitat.
Plants from areas with a Mediterranean climate like our own – where the year is divided into a short wet season followed by a long dry one – are partial to soil with an alkaline pH. This is why your Euryops daisy – that popular shrub with yellow daisies and finely cut, sea-green foliage – could not grow in your acid soil. The Euryops daisy is native to South Africa, whose Mediterranean climate means that the soil there has a high pH and the plants originating there require alkaline soil.
I highly recommend that you grow camellias. The camellia is an acid- loving plant that is reasonably drought-tolerant. In fact, I have seen camellias in side yards that receive irrigation no more than twice a month in the hottest weather and still produce an abundance of flowers each year.
Ferns are also acid-loving and not overly demanding when it comes to water. Interestingly enough, manzanita (Arctostaphylos species) is one California native plant that is partial to acid soil. A member of the Ericaceae or heather family, manzanita is a botanical relative of azaleas and rhododendrons. Certain species of manzanita are found growing in acidic soil habitats throughout our state. Many manzanitas, especially the sub-shrub and ground-cover types, would grow well in your partial sun exposure with a minimum of water.
Other plants well-suited to acid soil and our hot and dry Valley climate are junipers and arborvitae. Thirty or 40 years ago, junipers and arborvitae were a mainstay of Valley landscapes. Gradually, flowering perennials have taken their place. Yet, the simplest and most easily maintained landscape, whether your soil is alkaline or acidic, remains the juniper landscape. There is probably no better solution for a difficult-to-landscape and -irrigate slope than tam junipers (Juniperus sabina “Tamariscifolia”).
The tam juniper, as well as related varieties such as “Broadmoor,” “Arcadia” and “Blue Danube,” are famous for growing no more than 2 feet in height while spreading out 8 feet or more. Arborvitae are those chartreuse-colored, gumdrop-shaped shrubs that are planted near entry gates and along sidewalks or driveways. Dwarf arborvitae make nice additions to any planter because of their reasonable height (of 3 feet or less) and the distinctive color of their foliage.
TIP OF THE WEEK: Speaking of acidic soil, the presence of moss in your lawn may be an indication of low soil pH. The most effective chemical remedy to mossy soil is ferrous (iron) sulfate. Ferrous sulfate can be purchased or special-ordered at your neighborhood nursery. Just be careful when applying ferrous sulfate around sidewalks or other concrete surfaces – this is a chemical compound that will produce a rusty orange stain on such surfaces.