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When You Love Roses Too Much - Part 1

© Mark Whitelaw

I recently received an email from a gardener whose roses had developed long, unusually soft and floppy canes. She was concerned because the stems would not support the blooms, and feared the canes would snap in the wind. The problem was too much love. Well, too much fertilizer anyway.

Lured by the perpetual myth that roses are heavy feeders or by the desire to produce trophy-winning specimens, some rosarians provide too much "love" in the form of excessive fertilizations. Some have gone to the other extreme by providing too few nutrients, supplementing only with compost and mulches, and thus disregarding the special needs our roses require.

The rosarian must strive to achieve a nutrient balance within the garden - first, by performing a quality soil test to determine what is available; and second, to supplement those nutrients shown to be deficient. Once established, the rosarian can determine when these nutrients go out of balance (or when they are consumed) by understanding the indicators of those imbalances.

Rose nutrients, like most plants, are chiefly divided into two groups - macronutrients, those needed in larger quantities for survival, and micronutrients, those that supplement growth and are needed in lesser amounts.

The macronutrients are carbon, oxygen, hydrogen, nitrogen, phosphorus and potassium. Since the first three are provided by the air and water in the soil, we'll dispense with discussing their obvious need. Instead, we'll concentrate on those nutrients affected by soil conditions and pH, conditions you can control.

Chief among these is nitrogen - directly responsible for cell growth and respiration in plants. Without it, plantlife cannot exist.

The nitrogen form used by plants is called a nitrate. These may come from an application of a synthesized source like nitrate of soda or ammonium sulfate, or from the microbial transformation of a natural nitrogen source like manure, blood meal, cottonseed meal, alfalfa meal or feather meal.

When natural nitrogen sources are used, a transformation process called "The Nitrogen Cycle" must occur. These sources contain nitrites. They are transformed into ammonical nitrate compounds by fungi and bacteria, and therefore dependent on temperature, pH and soil friability. When soil temperatures near 40°F (4°C), the process is very slow. The rate of transformation doubles for roughly every 20°F increase in soil temperature provided the soil pH is not too low (too acidic). When soil pH drops below 5.5 (when it becomes acidic), transformation is also very slow. "Denitrofication," the transformation of nitrates into free nitrogen, can occur where soils are compacted. Free nitrogen cannot be consumed by the rose, and is subsequently lost to the soil or atmosphere.

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