by Ronald G. Schwerdt
3019 N. Major Ave. | Chicago, IL
Email: rgschwerdt@aol.com

Are your roses growing as well as they can? There may be many reason why they are not performing as they should. Some problems have simple solutions, while others are a bit more complex. Many are physiological and not related to infectious diseases or plant pests. Most arise with the plant’s environment, such as the soil. Too much or too little water, poor drainage, insufficient soil aeration, or a nutrient deficiency, etc. may be the cause. These are conditions that need to be identified and eliminated in order to grow healthy roses.

It is a well-known fact that insects and diseases thrive on stressed and unhealthy plants. Start with a biologically active soil rich in humus. Under proper conditions of moisture and soil temperature, most species of soil organisms in the process of decomposition produces substances such as antibiotics, enzymes and trace elements that provide optimal plant growth, also help fight off diseases, resulting in a natural immunity for the plants – before insects or diseases can get established.

Not all problems related to unhealthy plants are caused by environmental conditions. Some problems can be traced to various insects that inhabit the soil, such as nematodes, fungus, gnats, etc. They can feed on plants’ roots and spread diseases showing symptoms similar to plant dehydration, and yet not be caused by a lack of moisture in the soil.

While rosarians will agree that water is of the utmost importance for growing roses, so is proper soil management. Part of this “management” is conserving soil moisture for as long as possible, by any and all means. The best method of conserving moisture is to incorporate organics regularly, like sphagnum peat moss or compost, to build up a live healthy soil. This results in improved soil aeration as well as improving the tithe (workability) of the soil. Opening up the soil for greater air infiltration makes for quicker decomposition of organic matter. This organic material feeds the soil’s active microorganisms as it decomposes, thereby building the soil structure, ensuring a constant supply of nutrients and humus, which acts as a reservoir for storing soil moisture.

During hot, dry periods, with a breeze, the loss of moisture will be greatly increased. Having a limited root system and large top growth during these hot dry periods causes some plants to dry out quickly. Plants sometimes lose more moisture through the leaves, than the roots are able to absorb from the soil, causing a temporary wilting of foliage. Water, along with dissolved nutrients, are pulled upward by capillary action under tension. Moisture flows from the roots through the xylem tubes to leaves, where it evaporates into the atmosphere (leaf transpiration), producing a cooling effect in hot weather. As long as the capillary action remains unobstructed, the plants receive an adequate supply of water. Repottimg a plant in an incompatible soil may result in a break of continuity of gravity’s pull of water by the roots.

Soil is the key to growing healthier roses. A garden soil is nothing more than a combination of rocks, worn down over the years by nature, into various-sized particles. These particles, from silt to coarser sand to very fine sand are combined with a various amounts of organic matter, such as peat moss, decayed leaves, etc.

There are basically 12 recognized types of soil structures that make up the physical structure of a soil, with the percentage of sand, silt and clay determining the class. These are light, medium, and heavy soils, depending on the degree of air infiltration, water and nutrients absorption. A basic formula is one third coarse sand, one third clay, and one third decomposed organic matter. When mixed together, these elements provide a soil mixture that is light and friable, doing what you want it to do. This is known as loam, and is what you should try to change your existing soil to, if need be.

A light soil is generally sandy. While providing excellent drainage and aeration, light soil also warms up quicker in spring; it is often on the acid side; and it lacks the ability to retain moisture or nutrients. To overcome these problems, a large amount of organic matter must be worked into this kind of soil.

The soil structures in many areas are clay or silty clay loam – a heavy soil. This makes it ideal to absorb and retain moisture and nutrients, but it suffers from poor drainage. To correct the drainage problem of a heavy soil (which you must do to get oxygen down into the root system), you must work in coarse sand (torpedo) and decomposed organic materials.

These facts stated, it becomes apparent that a medium-type soil structure is best – one which incorporates only the best features of clayey and sandy soils into one that is fertile, and well balanced. Any soil can be conditioned into one that will produce healthy roses by incorporating into it what the soil is lacking. Do not try to condition a soil that is too wet to work. All you will do is compact it, making it extremely difficult to condition afterwards.

Fall is often the best time to condition the soil, as there is still sufficient time to incorporate anything required to improve the soil , letting it mellow over the winter months for next year’s spring growth.

Soil aeration is necessary for soil’s microorganisms to function properly. This is vital in the utilization of plant fertilizer as they feed on the organic matter as they condition the soil. Over a period of time this organic matter is depleted and needs to be replenished. The more chemical fertilizer used, the quicker this will happen. For this reason, it is a good practice to incorporating some organic matter into the soil every year. Without these organisms and enough organic matter for them to feed on, any fertilizer you give your plants will be of little value.

You should have a professional soil test made at least every four years, sooner if you have problems with the roses. During the growing season, check the soil’s pH yourself. Soil testing kits and meters are available that are easy to use. Even though there are indications that the soil is lacking in a certain element, the element may be present in the soil, but because it is locked up by a too high or too low pH, it is unavailable to the plant. Adding fertilizer to a plant suffering poor growth is of little use unless a soil is first conditioned to a level where the plant can take up and utilize the available nutrients. The pH in a soil is commonly referred to as the acidity/alkalinity balance. On a scale of 0 to 14, 7 is neutral. Above 7 is alkaline, below 7 acidity. For roses, the pH range should be between 6.0 and 7.0, with 6.5 ideal.

Sulfur is usually used to lower the soil’s pH, while dolomite lime is used to raise it. Dolomite lime is also a source of calcium and magnesium. The quantity to use to raise or lower the pH to the desirable range is on the box. Claims are made by many rosarians that Epsom salts (magnesium sulfate) agricultural grade encourages basal breaks. There is a great percentage of sulfur (S) 12.9 percent in a 50# bag, and magnesium (Mg) 9.8 percent. If you already have a soil on the acidity side, adding sulfur will lower your pH further! Be wary of the ashes from some types of briquettes used for outdoor cooking. While many are a source of potash, some contain a high level of sulfur. This, when combined with water, forms sulfuric acid, which again lowers the pH of your soil.

Gypsum (calcium sulfate) does not change the soil’s pH and has the ability to loosen up a heavy clay soil. Soils high in excessive amounts of sodium salts sustain damage to their structure. Having an alkaline condition can cause the plant leaves to burn. Adding gypsum provides calcium that replaces the sodium in the soil’s structure. This breaks the sodium’s bond, allowing water to flush out the soil’s salt buildup from too much chemical fertilizer.

It is important to understand the relationship between water, soil and maintaining the proper soil pH. Make adjustments if need be, and when the new rose season is in full swing, take inventory of how the roses are performing in this new changed environment. If rose are still not up to your expectations, what are the problems? Is new growth stunted and puny looking, or are blooms or foliage of abnormal size?

Do you have healthy looking foliage, but no flower buds? How about color of the bloom? Are they washed out and faded looking, instead of deep vivid colors? Are leaves lime green or yellowish (chlorotic) color instead of the dark green which is normally associated with healthy foliage? Maybe something is missing or not being utilized in the soil.

There are times when a plant may show signs of a nutrient deficiency even after being fertilized. These signs include a lack of color in the blooms, stunted plants, some leaves turn light green, white, dull gray, yellow, etc. All these symptoms can be caused by a lack of one or more trace elements (not all fertilizers contain trace elements.) A trace element can provide a plant and the soil bacteria with a balanced nutrition. When using a trace element, only a very small quantity is necessary.

One example of a nutrient deficiency occurs when trace elements are used up in the soil, causing the leaf to turn yellow while the veins of the leaf remain green. This condition usually occurs when there isn’t enough magnesium which the plant uses to manufacture chlorophyll in the soil. Yellow leaves (chlorotic) are a good indication the plant has some type of a physiological problem, a nutrient deficiency, or a problem with the plant’s environment.

While there are many reasons that cause leaves to yellow, their symptoms can be confusing. Often leaves look like the discoloration could be caused by a shortage of several different elements.

A nutrient deficient plant is plagued by insects and diseases more often than a healthy plant.

This article was provided to the TVRS as a courtesy by the American Rose Society.

by Dr. Gary A. Ritchie • 8026 61st Ave. NE • Olympia, WA 98516
Email: rosedoctor@comcast.netImagine for a moment that you are a nanoperson who can crawl inside a rose leaf. What would it look like? What would it feel like? What sorts of structures would you see?

Above you there would be masses of green, tightly packed cells arranged in palisades. At mid‑leaf, where you are, the cells become loosely packed with large air spaces between them. The surfaces of these cells are wet to the touch. The air is very damp – 100 percent relative humidity in fact. Throughout this labyrinth of cells you see complex systems of pipes running to and from each cell. Some (called xylem) are filled with water, while others (called phloem) are filled with a sugary solution. These are the leaf veins that ultimately connect the cells to the rest of the plant.

Below you is a dark green carpet of thin, tightly interconnected cells – the epidermis – which is covered on its outside by a thin layer of wax called the cuticle. Scattered across the epidermis are thousands of tiny windows leading to the outside world. These windows are the stomata. In previous articles we’ve mentioned stomata in several contexts, but have never discussed them in any detail. Here we will explore what stomata do and how they work.

The main thing stomata do is to open and close. When they are open, gases inside the leaf, such as water vapor, carbon dioxide (CO2) and oxygen, diffuse out of the leaf into the atmosphere. The diffusion of water vapor from the leaf is called transpiration. CO2 that diffuses out is a byproduct of respiration, while the oxygen that escapes is a byproduct of photosynthesis.

Correspondingly, CO2 from outside the leaf can diffuse into the leaf, providing your rose with the carbon it needs to make food. This exchange of gasses is absolutely critical – without stomata plants could not live, life on Earth would cease, and the stock market would tank.

The stomatal pore is not actually a structure in itself. Rather, it is a space created when two cells, called guard cells which are embedded in the epidermis of the leaf, become either turgid (filled with water) or flaccid. The drawing at right shows how this happens. The guard cells are shaped like tiny kidney beans. When they are flaccid there is no space between them – i.e. the stomate (singular of stomata) is closed. But when they are pumped full of water, they stretch and pull apart in the middle, forming a pore.

Ideally, it would be advantageous to plants if stomata were always open. This would allow transpiration and photosynthesis to proceed continuously.

Transpiration is important because it pulls nutrient ions up into the plant, and it cools the leaves on hot days. Photosynthesis is important because it produces food. So, for the plant to gain both nutrients and food the stomata must be open. But this is problematic, because when stomata are open transpiration sucks water from leaves, causing them to dehydrate. When leaves dehydrate, stomata close blocking the uptake of CO2. So the plant must strike a balance between absorbing CO2 while not depleting its internal water balance.

To realize these conflicting objectives, hundreds of millions of years of plant evolution have created an exquisite array of interacting mechanisms and feedbacks. These control and optimize stomatal movement. For example, stomata close in darkness and open in light. The logic for this is clear – photosynthesis requires light. Stomata close when the leaves begin to dry. Again, this is a mechanism that preserves leaf moisture and prevents dehydration. They also close when humidity is low and when the CO2 concentration of the internal leaf atmosphere is high.

Stomatal opening and closing are modulated by what is know as a “potassium pump.” Potassium ions (K+) contained in the guard cells influence their osmotic properties. As the K+ concentration increases, the cell osmotic potential drops. This pulls water into the guard cells, opening the stomata. This active process accumulates potassium ions against a concentration gradient. Therefore, it requires that the plant expend energy.

An amazing discovery was made recently relating stomata to global climate change. Plant physiologists found that stomatal frequency (number of stomata per unit of leaf area) is directly related to the ambient atmospheric CO2 content – as CO2 increases, stomatal frequency decreases. Paleobotanists (kooks who make their living studying plant fossils) can use this relationship to reconstruct ancient CO2 profiles. First, they determine the age of fossil leaves, then they count their stomatal frequency. The more stomata that occur on the leaves, the lower the atmospheric CO2 was when the leaves were formed. This, then, provides a very long-term record of atmospheric CO2 concentrations. Pretty cool stuff.

Other interesting research conducted several decades ago involves indirect stomatal responses to the environment. Scientists found that when soil moisture begins to decline, ever so slightly, around a plant’s roots, the young root tips are able to perceive this stimulus. They then send chemical signals (hormones) up to the leaves that tell the stomata to close in “anticipation” of pending drought.

While this is a very interesting phenomenon, it’s also a great lead‑in to the next series of articles. There we will explore plant hormones – the chemical messengers that move around in plants and tell them what to do and when to do it. You won’t want to miss this, so stay tuned.

This article was provided to the TVRS as a courtesy by the American Rose Society.