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When You Love Roses Too Much - Part 2

© Mark Whitelaw

Minor nutrients, although needed in lesser quantities, are nonetheless important to the rose's diet. Without them, growth is stunted, leaves are malformed, and blooms fail to mature.

Minor nutrients

Magnesium, expressed as Mg, is essential to photosynthesis in plants. It's the "main molecule" in chlorophyll, the green coloring in green plants! Photosynthesis is the process by which plants use the sun's energy to create carbohydrates.

Without magnesium, the rose's leaves turn yellow or purple (usually at the bottom of the shrub) while leaf veins remain green. Although the plant will maintain a normal growth rate, leaves will fall prematurely from the base of the plant. Magnesium usability is limited to a narrow range in soil pH; even slightly acid soils will inhibit its usefulness.

We usually think of calcium (Ca) — found in milk and limestone — as bone material. Actually, calcium is a metal and extremely important to the rose for its ability to neutralize toxic acids formed in their metabolic processes. It also serves as the building block in plant proteins and cells, and assists in the balance of magnesium within the plant's growth cycle.

If your roses are displaying uneven growth, a calcium deficiency may be the culprit. Leaves at the top of the shrub will display brown, dried centers, and leaf tips may curl. This is common in excessively low pH soils. Excessive calcium will result in a boron or magnesium deficiency.

Boron (B) is essential to virtually every function within the rose's metabolism: its cell growth and division and its flower formation and pollination. Although normally found in well-prepared soils, boron deficiency usually occurs in high pH soils because of an abundance of calcium.

A deficiency will manifest as overly crowded leaf growth and new leaves near the shrub's top may appear as a mottled yellow and malformed. Excessive boron will appear as brown leaf edges with a characteristic pink margin separating the brown leaf tissue from the green leaf tissue.

Sulfur is expressed as an S and is an essential organic compound in the formation of plant proteins and amino acids necessary for root development and cell protoplasm. Normally, sulfur is available from organic materials and is converted by bacteria into soluble and usable sulfates.

Sulfur deficiency is noticeable on the top leaves of the plant. Leaf tissues are very pale and veins appear yellow. Too much sulfur in the soil will manifest as excessively low pH, causing other nutrient deficiencies.

Iron is expressed as Fe and, like magnesium, iron is an essential catalyst to the photosynthetic and hydrocarbon production process. Without iron, the plant is said to have "iron chlorosis" which manifests itself as yellowish leaves and dark green veins. Leaf stems turn yellow. Unlike magnesium deficiency which occurs near the bottom of the plant, iron deficiency usually begins at the top of the plant and works downward. In highly alkaline soils, iron becomes an insoluble precipitate and cannot be used by the plant. Keeping soil pH at or below 7.0 allows available iron to be used.

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