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Photograph by Shari Kaplan
The genus 'Campanula' is comprised of a large number of bellflower species, which vary in flower color and size and leaf shape. Most make good groundcover.
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How and where to use soil amendments: a user's guide
By Tony Tomeo
Last Saturday as I was working in the vegetable garden, I incorporated into the soil some of the organic amendments I discussed last week.
After many years of cultivation, the soil is of very good quality, but it benefits from fresh amendments to replace what has decomposed during the past year. Every year, quantity and quality of amendments is determined by the condition of the soil.
Initially, amendments were added very generously to the soil, to compensate for many years of use as a parking lot by cars that leaked automotive fluids. Now, the soil is so rich it would likely be very productive for many years without additional amendments.
Although organic soil amendments are used in large quantities, there are no specific directions for proper application. Each situation has specific requirements.
Some horticulturists recommend adding as much as an equal volume of amendments for an equal volume of soil, if the soil is of poor quality. In my garden, however, I don't think I have ever added more than one part amendments to three parts soil, even when the soil was of very poor quality.
If too much amendment is added at one time, the soil slowly collapses (sinks) as the amendments decompose. Of course, more amendments may be added over the years to compensate for decomposition. Lawn areas are usually not amended as deeply, so soil collapse may not be as noticeable. If it becomes a problem, shallow depressions in lawns are easily filled.
Additions of smaller, but still generous quantities of amendments, may not perfect the soil in one year. Similar quantities, however, may be added for several years, until only minor amounts are required. Annual soil conditioning is very practical in areas of the garden that are cultivated regularly, such as beds of annual flowers or vegetable gardens.
Amendments should be incorporated very thoroughly, and clumps or clods of dense soil should be crushed. The depth of incorporation is determined by what is to be grown. For example, petunias grow well in soil that has only been amended in the top few inches. Larger types of dahlias, however, prefer a deeper volume of amended soil. Amendment to about 18 inches is ideal for most annual and herbaceous plants.
Areas that are permanently landscaped cannot be conditioned as easily. Woody trees, shrubs and vines may be damaged by soil disturbances. For such application, soil amendments are used only once during installation to help roots of new plants become established.
Because most roots are dispersed in the top 18 inches of soil, amendments need not be added below newly installed plants. Such superfluous amendments will only cause problems as they decompose, causing the maturing plant to sink into the soil.
Although generous quantities of amendments are recommended for new installation, backfill soil (existing soil after it is mixed with amendment) should not be so different from the surrounding soil that root dispersion is inhibited. If backfill soil is too rich and surrounding soil is too dense, most root growth will be limited to the volume of soil that was amended--similar to growing in rich soil contained in a "clay" pot.
Flower of the Week: Italian bellflower
Although it is not very common in nurseries, Italian bellflower, Campanula isophylla, is often found in older, established gardens where it has naturalized. Those who recognize and appreciate it will leave it when pulling weeds. Like most small, trailing bellflowers, it prefers to grow in part shade under larger species. Regular irrigation and rich, well-drained soil are ideal.
The perennial stems trail, or hang, to two feet and are useful for small-scale ground cover, or in containers with larger specimen plants. The delicate, light green foliage is serrate and about 1 1/2 inches long. The pale blue flowers are about 1-inch wide, but are star-shaped rather than shaped like typical bellflowers. The cultivar 'Alba' produces larger, white flowers. The bloom cycle begins in late spring, but is more profuse later in summer and into autumn.
Italian bellflower is easily propagated from trimmings of established plants. Because stems root as they trail on the surface of the soil, sections of larger clumps are easily divided. It is not popular enough to be stocked by the more basic nurseries or home improvement centers, but may be found in some of the more specialized nurseries.
Horticulturist Tony Tomeo may be contacted at 408.358.2574.
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Los Gatos, California Since 1881
