We kicked off this series with the idea that “You are what you eat,” and that the saying could also apply to our roses. Growing healthy roses that produce bountiful blooms and are able to fend off disease requires, in addition to the basics of light, moisture, air, balanced nutrition – having the right nutrients present and available to the plant when they’re needed is just as important. Here’s a summary of the many aspects of plant nutrition and “feeding” roses that we’ve covered in the past months:
What a fertilizer is and what it does
Plant nutrients are the chemical elements taken in by plants that are essential for their growth and development. A fertilizer is a material added to the environment around the plant that directly impacts the plant, providing it with specific nutrients. Fertilizers are NOT plant food! Plants make their own food (sugars and carbohydrates) using water, carbon dioxide and sunlight and combine them with plant nutrients to produce the proteins, enzymes and vitamins essential to plant growth. When we fertilize, we are applying plant nutrients to supplement nutrients naturally occurring in the soil.
The seventeen different chemical elements for healthy plant growth are broken down into four general groups. The essential elements - carbon, hydrogen and oxygen, are derived primarily from air and water. The primary or macronutrients - nitrogen, phosphorus and potassium, are the most common fertilizer ingredients. Secondary nutrients along with micronutrients or trace elements - calcium, magnesium and sulfur, boron, chlorine, copper, iron, manganese, molybdenum, nickel and zinc, play varying roles in plant growth and health.
Types of available fertilizers
Fertilizers contain an active ingredient - the specific material responsible for the intended beneficial purpose of the product. They can also include inert ingredients (often referred to as filler) - substances other than an active ingredient intentionally included in a fertilizer but have no intended nutritional value. Chemically based fertilizers are simple compounds derived from naturally occurring chemical elements; while naturally-based fertilizers are derived from organic materials - bone meal, kelp meal, fish emulsion and manure are commonly used organic fertilizers.
Many varied forms and formulations are available - liquids or solids, simple or single nutrient fertilizers, soluble complete fertilizers, slow-release fertilizers and multi-purpose products that feature a fertilizer and additional materials that serve a different purpose (like a fungicide or insecticide).
How and when to fertilize
How you apply fertilizer depends on what you are adding and when. Granular, powder or pelleted-type fertilizers are generally scattered around the base of the plants and lightly scratched into the soil. Water-soluble products can be simply mixed with water can and applied directly to the soil plant, or sprayed directly on the foliage.
Don’t waste your time, energy and money by fertilizing at the wrong time. Too early in the year and all your valuable nutrients may be washed away by seasonal rains; too late in the season, the plants are starting to shut down and don’t need the extras. For established plants, time your application to maximize the benefit of your fertilizer so that nutrients are available to the plant when it needs it most – during the active growing and blooming stage. The frequency of application will depend on what you’re after – bountiful blooms or that Queen of the Show, the quality of your soil, and the weather. If your roses are planted in healthy soil that is rich in organic materials, you generally don’t need to add any fertilizers until after the first big bloom.
To protect your plants from damage, make sure to water the plants thoroughly the day before and after fertilizing. Adding fertilizers, especially inorganic ones, to a dry plant can result in leaf burn or worse. Watering after fertilizing helps move nutrients into the root zone. When doing a foliar application of fertilizer, do it early in the morning when the liquids will be absorbed most quickly, won’t burn foliage and the leaves have time to dry completely.To protect your plants from damage, make sure to water the plants thoroughly the day before and after fertilizing. Adding fertilizers, especially inorganic ones, to a dry plant can result in leaf burn or worse. Watering after fertilizing helps move nutrients into the root zone. When doing a foliar application of fertilizer, do it early in the morning when the liquids will be absorbed most quickly, won’t burn foliage and the leaves have time to dry completely.
Amendments and additives
An amendment is any material mixed into the soil that indirectly aids plant growth by improving the condition of the soil, like its structure or texture, water retention or microbial activity. The terms soil conditioner and amendment are often used interchangeably, both serving to improve the chemical, physical or biological properties of soil. Mulches are organic or inorganic materials placed on the soil surface to help prevent weed growth, conserve moisture and add organic matter to the soil as they break down. Some materials used as soil amendments can also act as a fertilizer by providing nutrients to the soil, or be applied to the soil surface as mulch.
When selecting an amendment, consider what you want the amendment to do, how long the material will last in the soil, whether it retains water and / or improves permeability (the rate at which water moves through the soil), or if it may present any problems from excess salts, weed seeds, plant, animal or human pathogens. Also think about the practical aspects of the material like availability, cost and ease of handling.
How much of the amendment you add will vary depending on the condition of the soil you’re working with, what you’re adding and what you want it to do to the soil. Over-amending can be a problem if you’re trying to fix a soil problem by adding large quantities of amendment in a single season, and result in soil that is high salts or ammonia that burns roots and leaves, low nitrogen levels from the tie-up of nitrogen due to a carbon to nitrogen ratio imbalance or retaining too much water.
Deficiencies of an individual nutrient can result when there is an inadequate amount of a specific nutrient in the soil or it is unavailable to the plant (most commonly due to incorrect soil pH or being tied up with other nutrients). Typical symptoms of nutrient deficiencies are reduced shoot growth and leaf size, leaf chlorosis (yellowing of leaf tissue due to a lack of chlorophyll), necrosis (death of plant tissue) and die-back.
Some nutrients can move easily through the plant (they’re mobile) while others cannot. If only the lower leaves of the plant are affected, then a mobile nutrient is the likely culprit. Conversely, if it’s the upper leaves showing the deficiency, the plant is likely deficient in an immobile nutrient, one that cannot move from older to newer leaves. The most common deficiencies in roses are nitrogen and iron. Nitrogen, along with phosphorus and potassium, can readily move through a plant while iron is immobile and cannot get to the newer growth.
Nutrient toxicity, the accumulation of soluble salts in the soil, is not uncommon in the rose garden, prevalent in most water sources, fertilizers, manures and Epsom salts (magnesium sulfate). They cause damage to foliage - marginal browning of leaves beginnings at the tip and proceeding to the base of the leaf along the edge of the leaf, and can also retard overall plant growth.
Here’s to a balanced diet and good nutrition – for you and your roses!
Photo of Soaring Spirits is by the author, Nanette Londeree
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