Roses Come Clean

An organic approach to rose care yields healthy, beautiful results.

By G. Michael Shoup


Embrace Nature's Ways 

When we were establishing our display garden, applying the recommended 10-10-10 synthetic fertilizer to the roses was laborious and resulted in plants that became less and less vigorous over time. Weekly spray sessions of insecticides and fungicides did little to stop pest invasions; they were effective only at curtailing our enjoyment of gardening. One day, we spread several inches of bark mulch in part of the garden, and what happened next surprised us all: Plants in the mulched areas showed brighter and more vibrant leaves and were less affected by daily heat stress (no small consideration as our location is central Texas). 
This realization caused us to rethink the way we grew roses, challenging the conventional chemical-intensive methods. Our bark mulch replicated nature's recycling of leaves and organic debris on the forest floor. In successive years, we replaced chemical inputs with a variety of organic regimens, all based on what we saw in the natural environment.
Nobody fertilizes the flora in nature, but it grows and thrives just the same. Could we rely on nature's techniques for supplying nutrients to plants instead of buying bags of fertilizer? As it turns out, twice-yearly applications of coarse hardwood bark mulch (2 to 3 inches in February and again in September) provide all the nutrition roses need. Beneficial organisms in the soil—certain fungi, bacteria, and nematodes—assist in breaking down the mulch and feed on carbon released during decomposition. Gardeners tend to think of these organisms in negative terms, and indeed, the microbes that cause bacterial crown gall and powdery mildew, among other rose maladies, are bad. But there are many more organisms that improve the viability of plants through symbiotic relationships that make roots more efficient at seeking nutrients, or by converting soil nitrogen into forms that plant roots can absorb. Gardeners who are starting with nutrient-depleted soil might need to add a supplement of decomposed manure, compost, or other organic fertilizer to get the microbes rolling.
Brew Tea for Roses 
In retrospect, it is hard to believe that we spent years destroying these microbial populations through our spraying program. A change as simple as adding mulch had improved the health of our plants, yet there was something even more magical—dare I say miraculous?—that evolved from this discovery. Elaine Ingham, Ph.D., a soil microbiologist from Oregon, introduced us to a revolutionary process of increasing beneficial soil organisms by aerating freshly leached compost tea. While traditional compost tea is brewed simply by suspending a "teabag" of compost in a bucket or barrel of standing water, the aerobic technique uses an air pump to continually bubble oxygen through the liquid in a brew tank. 
We followed Ingham's instructions, blending chlorine-free water, molasses (a food source for microbes), fish hydrolysate (ground fish carcasses, another food for fungi), humates (organic residues of decomposed plants or animals), and a handful of good compost to provide the initial microbial population. The air pump kept the mixture in a state of constant agitation and aeration.
According to Ingham's research, after 24 hours of aerobic brewing, the microbial population explodes exponentially. One milliliter (about one-fifth of a teaspoon) of aerobically brewed compost tea contains a trillion bacteria, representing 20,000 different species, and a much-increased fungal biomass—all multiplied from the initial organisms in the compost. Researchers caution that molasses and other microbial foods used in brewing compost tea can boost the levels of pathogenic bacteria, such as salmonella and O157:H7 E. coli. Because of this significant health concern, aerated compost tea should be used with care, and should not not be used on food crops.
The ability of compost to aid the soil's capacity to retain water, improve soil porosity, and help plants absorb nutrients and minerals has long been understood. But I was surprised at the results of spraying compost tea directly on rose foliage. The vast number of beneficial microbes in the tea defended our plants from the "bad guys," like black spot and mildew. It was described to me as like having an auditorium filled with healthy friends: If someone sick with a flu bug tries to enter, all the seats are taken. Treated plants were less prone to attack by red spider mites.
We began spraying weekly during spring and fall (the seasons when roses in Texas grow actively), wetting the leaves thoroughly. Within 6 months, the improved health and vigor of our gardens proved that we were on the right track.