A rose that has either too much or too little of any nutrient will suffer. Most of these nutrient imbalances can be diagnosed by using color photographs {See color chart of nutrient deficiencies at end of chapter.) There are 16 nutrients that roses need and thus there are 32 possible imbalances of nutrients, plus some other toxicity effects such as too much sodium.
Fortunately, there are only four of these imbalances that are frequently observed, and it is important that the Consulting Rosarian is aware of them. These are:
- Nitrogen deficiency. Because nitrogen can leach from the soil (as nitrate), volatilize (as ammonia) or denitrificate (by bacteria), nitrogen needs to be constantly added to the soil. In roses lacking nitrogen, the leaves will show an overall pale yellow-green color, the plant will be stunted and stem size will be smaller than normal. This can be caused by a too high or too low a pH.
- Oxygen deficiency. This is a lack of air to the roots typically caused by over watering or poor drainage. The veins of the leaf will show chlorosis (yellowing) followed by interveinal chlorosis.
- Iron deficiency. The appearance of leaves on a plant suffering from iron deficiency has the opposite look of oxygen deficiency – the interveinal areas show chlorosis while the veins remain green. It is rare that iron is actually deficient in the soil, but rather it is likely that something is making the iron unavailable. Possible causes are high pH, poor aeration of the soil, high soluble salts or excessively high concentrations of manganese, zinc or phosphorus. Foliar sprays can give temporary relief if they contain iron. This may also be caused by too high or low of a pH.
- Leaf burn. he edges of the leaves turn brown and crispy. The fundamental cause of this is a lack of water getting to the edges of the leaves. This can be caused by anything that either makes water unavailable to the plant or excessively increases the water loss from the plant. Typical causes include over fertilizing with synthetic fertilizers, high salt level in the soil, lack of water, heat stress, spray burn or a combination of the above
Symptoms of Rose Nutrient Deficiency
It is important to note that many symptoms of a nutrient deficiency are problems with availability rather than supply. The nutrients may be present in the soil but are unavailable because of a pH that is too high or too low. There may also be a nutrient imbalance that prevents absorption of one nutrient thus causing symptoms of deficiency. Many symptoms are similar. Generally, micronutrient deficiencies are rarely seen. The most common deficiencies are nitrogen, iron, oxygen, plus heat stress. See the Color Plate of Common Rose Deficiencies at the end of this chapter.
1. Mature Leaves Affected First
- Older leaves turn chlorotic, pale light green to completely yellow on the entire leaf but remains on the plant. Reduced growth with reduced leaf size. Stems weak and spindly, small flowers, lighter in color. – Nitrogen Deficiency
- Do not mistake oxygen deficiency with a nitrogen deficiency. Though the symptoms look alike, no amount of nitrogen will correct the symptoms.
- The first symptom is a reduction of leaf size. Entire leaf is chlorotic with yellow between veins. Plants are stunted with large, necrotic white areas symmetrically distributed on both sides of the leaflet between larger lateral veins of the older leaves. Leaf edges of older leaves cup down. Some varieties may develop dark brown or purplish blotches scattered randomly across the leaflet. – Magnesium Deficiency
- Older foliage drops without turning yellow. Leaves are dull gray-green in color. Buds slow to develop, leaf edges of older leaves may cup down. – Phosphorus Deficiency
- Margins of leaf are affected first. Margins become yellow then turn brown, leaves sometimes become purple. Young shoots become hardened and stunted. Flower buds may be distorted. – Potassium Deficiency
2. Younger Plant Parts Affected First
- Chlorosis of young leaves. A general lightening of the green of the leaves. Interveinal areas yellow. – Iron Deficiency
- Interveinal areas yellow but smallest veins remain green, more of a netted appearance. – Manganese Deficiency
- Shoots often die or are hard. New growth ceases or withers. Leaves do not develop or are distorted. • Flower petals become shortened and bullheaded flowers may be numerous with petals rolled inward. – Boron Deficiency
- Young leaves develop light edges, apical stem dies resulting in development of many small side branches. Possible to confuse with magnesium deficiency. – Copper Deficiency
- New growth dies without development. In severe cases, plants become defoliated. Many dead roots. • Older leaf edges may cup down. – Calcium Deficiency
NOTE: There is a close relation between calcium and boron. Calcium deficiency symptoms may be only a reflection of a calcium-boron imbalance. There must be ample quantities of both, but they must be present in proper balance. Often low pH, high phosphorus and high nitrogen levels, high soluble salts and heat stress create conditions which limit calcium uptake.
- New shoot growth aborted, distorted leaves. Older leaves do not cup down. – Zinc Deficiency
- Symptoms are similar to moisture stress with youngest growth displaying some wilting. Weak flower stems and leaves drying from the tips and edges are also noticed. – Molybdenum Deficiency
Symptoms of Nutrient Toxicity
1. Mature Foliage Affected First
- Older leaves drop rapidly with necrotic leaf margins. – Spray Injury
- Older leaves do not drop at first, main vein remains green as the leaf first turns yellow then brown, then leaves drop after drooping. Young shoots become stunted, buds may be distorted. – Zinc Toxicity
- Browning of mature leaves at the leaf edge, separated from the green tissue with a distinctive pink margin, brown, irregular spots, then eventual leaf drop. – Boron Toxicity
- Small black spots on older leaves. May also cause iron deficiency symptoms to appear. – Manganese Excess
- Similar to high salt concentrations, followed by rapid falling off of older leaves. – Sulfur Toxicity
2. Younger Plant Parts Affected First
- Younger plant parts are affected first with chlorosis of terminal growth. Buds fail to develop after cutting. Too much urea may cause plant hardening. Often the foliage is increased in size and blooms smaller than normal. -Nitrogen Excess
- Symptoms of copper, iron and zinc deficiencies will occur with excessive use of phosphorus as it makes these elements unavailable to the plant. This is especially true with a low pH. – Phosphorus Toxicity
- Chlorosis, root loss and wilting of young shoots. – Potassium Toxicity
Heat and Moisture Stress
Although not technically a deficiency, heat stress symptoms are similar to nutrient deficiencies and will be covered in this section. Visual symptoms will vary depending on the severity and longevity of the stress. Soil salts can become a problem in dry soil and cause root injury, which in turn causes wilting of shoots and leaf scorch. Sometimes scorch of the leaf margins may develop on immature or nearly mature leaves; especially those exposed to direct sunlight.
Heat stress is often noticed after a period of cloudy, rainy weather promoting succulent top growth, followed by hot, dry, sunny days. The lack of oxygen in the soil caused by excessive rainfall (and possible poor drainage) puts the plant under stress to withstand the quick respiration of hot weather. Wilting of young growth may occur at this time.
Bull nosed bloom formation of roses is essentially a temperature stress problem. Red flowers are more likely to develop bull noses than light colors. The darker pigments apparently absorb more heat during the sunlight hours and re-radiate more heat at night establishing a greater temperature fluctuation within the bud.
Petal edge burn is more noticeable in red flowers and is associated with the buildup of heat in the petals. This is more evident after extended periods of cloudy weather followed by hot, sunny days.
When air temperature is high, relative humidity low and air is moving across the leaf surface, the demand for water is greatest. Under these conditions, it is essential to provide water to the soil to reduce the total stress on the plant. During the hottest part of the day, it may be beneficial to water overhead. This will reduce the air temperature while providing moisture for the plant.
Effects of Soil Salts
Since roses are usually heavily fertilized, an accumulation of soluble salts is not uncommon. This could result in foliage injury and retarded growth. The effect of such salt accumulation is interference with water availability in the root zone. The higher the salt contents of the soil, the greater the stress on the plant to obtain moisture from that soil. Thus roses growing in soils having high salt concentrations tend to induce a physiological drought in the plants. This effect is intensified as the moisture content of the soil decreases.
All soluble salts do not have the same effect on the soil. Some present a more potent risk of injury by inducing physiological drought. Many of the high analysis fertilizer materials commonly used on roses are capable of producing a high salt index. However, when applied in suitable amounts for fertilizer response, the salt effect is usually not a problem.
A given concentration of soluble salts may not be injurious if the soil is kept moist and evaporation rates are low. But given the opposite conditions, the same salt concentration can cause root injury, which in turn cause wilting of shoots. All waters, except distilled, most rain or melted snow, contain some dissolved salts. Common components (ions) of salts contained in water supplies are calcium, magnesium, bicarbonate, chloride, fluoride and sulfate. Calcium, magnesium and potassium are plant nutrients, but can cause reduction in plant growth when present in excess of requirements.
Chlorides are especially injurious causing reduced plant growth and leaf drop. As the soil becomes solution becomes more concentrated. A concentration of dissolved salts, which is safe when the soil” moist, may become toxic when the soil becomes dry. It only takes one drying cycle under these conditions to cause the loss of roots, causing the plant to lose leaves.
The term salt index is used by scientists to indicate the relative physiological drought inducing effect produced by an equal weight of any fertilizer. Nitrate of soda, muriate of potash and ammonium nitrate are capable of inducing high salt effects when applied in any but moderate amounts. Other materials, notably the phosphates, ammoniated or otherwise, have a relatively low salt index.
It is important for the rose grower to appreciate the importance of water in the use of fertilizer material capable of inducing high salt effects. Small applications of water tend to dissolve the fertilizers and to develop the highest soluble salt concentration possible in the root area. Applications of water which cause some, but not too much, leaching tend to affect a loss of such materials as sulfates and chlorides, with little loss of ammonium or potassium, thus minimizing an increase of salts. Moreover, such watering gives good distribution of applied fertilizers. This is why one should never feed roses if the soil is dry and adequate watering should be done after fertilizing.
Where water is used conservatively, i.e.sub-irrigation, the salt concentration of the water supply is of the utmost importance. Because this method of watering is highly conducive to salt accumulation, sub-irrigation is not suitable for use with water supplies having more than low to medium amounts of soluble salts. If drip irrigation is used, the water supply should be tested for soluble salts. If the analysis is high, a watering system that delivers a greater quantity of water at one time should be considered. All soluble salts are not equal in the effects on rose plant growth when they are present in excessive amounts. Plants will tolerate relatively large amount of sulfates as salts of calcium and magnesium and even of potassium. Nevertheless, the treatment for the correction of high salt accumulations is the same- remove them with water. If drainage is not satisfactory, it may be advisable to add gypsum before leaching. Gypsum tends to improve soil aggregation and consequently the drainage of water. It is also very effective in displacing or facilitating the leaching of other salts from the soil. The liberal supply of calcium in gypsum exchanges places with other metal ions held in the soil and can be tolerated by plants to an unusual degree.
Growth retardation of roses from the effects of an excessive accumulation of soluble salts in the soil is indicated by electrical conductance tests on soil samples. A high salt index may not be as harmful in winter as in summer. Injury is most likely to result during hot, dry days of summer.
Spray Burn
A common symptom that is misdiagnosed is damage from spray burn. Some pesticides will cause damage naturally or if not used properly. Rubigan (Recommended for use as a foliar spray. Do not apply through any type of irrigation system). Daconil (Cannot be shipped to some states. If you don’t see it on the shelf at your local garden supply store, it most likely is banned in your area. It is listed as Danger/Poison) is known to cause spray damage.
ACKNOWLEDGMENTS
American Rose magazine, American Rose Society
Western Fertilizer Handbook, California Fertilizer Association, 9th ed., 1990
All About Roses, Dr. Tommy Cairns, Ortho Meredith, 1999
Roses, Roses, Inc. 1987 Steve Steps, Saratoga, CA