Plant Nutrition

Geranium with “Brown Speckle” Symptoms Due to Low pH

The symptoms on this geranium are due to iron and manganese toxicity, a nutritional disorder associated with low growing medium pH (below 6.0). This problem is sometimes called "bronze speckle" due to the numerous small brown spots on the leaves. Zonal geranium, American marigold and all types of impatiens are susceptible.

See the fact sheets: pH and Fertility Review for Annuals, University of Massachusetts

Drought Information

The drought this summer has been a challenge for some growers. Many towns have water bans and some towns have discouraged new plantings. Some retailers have reported that the hot, dry weather has also reduced demand for plants. Depending upon the water source, another consequence of the drought may be the quality of water being used for irrigation. Equipment clogged with sediment (surface water), or high salt (Na and Cl) concentration in irrigation water due to low water levels are possible considerations.   

Garden Mums, Flowering Cabbage and Kale - Irrigation and Hot Temperatures

Production areas with black fiber cloth were hot, hot, hot this week. Garden mums, flowering cabbage and kale may exhibit signs of wilting during extended periods of 90 plus degree temperatures. The solution may not be as easy as turning on the irrigation. Plants wilt when the soil is dry, but wilting will also occur in hot weather which may cause plants to be stressed, or if the roots are damage from a root disease such as Pythium, even if the soil is saturated with water. When the roots stop functioning the plants will show signs of stress by wilting.

Soluble Salt Injury - Spinach Transplants

Two photos of spinach plants in organic growing media. The compost mix (from the bag) tested high soluble salts (3.4 mS/cm) and ammonium (64). Spinach plants on showing symptoms of high soluble salts are stunted, yellowed and have burned leaf tips. Plants were also bottom watered with additional organic fertilizer. Notice the soluble salt build-up on the media surface. The spinach plants in the second photo are the same plants after a week of watering with clear water from the top and letting water drain through, leaching out the soluble salts.

Iron Deficiency on Petunia and Calibrachoa

Iron deficiency symptoms have been observed on petunias. At this time in the growing season, Iron (Fe) deficiency symptoms are starting to appear on bedding plants and other spring greenhouse plants. The main symptom of Iron (Fe) deficiency is chlorosis or yellowing, usually starting at the shoot tip and newly developed leaves. The yellowing or chlorosis may appear only between the veins (interveinal chlorosis) or the entire leaf may be chlorotic. As the problem gets worse the color of the chlorosis may change from yellow to white.

Geraniums - Nitrogen and Magnesium Deficiency

Because of cool temperatures some growers have been fertilizing geranium hangers at very low rate. However with the increase in the angle of the sun and increasing day temperatures in the growing the plants are pushing more growth therefore requiring more nutrients. This has resulted in plants showing nitrogen and magnesium deficiency. Nitrogen is an important component of nucleic acids, amino acids, enzymes and chlorophyll in the plant. Deficiency of nitrogen may cause the plants to appear stunted with light green lower leaves while upper leaves remain green.

Geranium - Nitrogen Deficiency

When temperatures are cool during March, growers may fertilize geranium hangers at very low rates. However with the increase in the angle of the sun and increasing day temperatures the plants are pushing more growth therefore requiring more nutrients. This has resulted in plants showing nitrogen and magnesium deficiency in this photo. Nitrogen is an important component of nucleic acids, amino acids, enzymes and chlorophyll in the plant. Deficiency of nitrogen may cause the plants to appear stunted with light green lower leaves while upper leaves remain green.

“Brown Speckle” Symptoms Due to Low pH

A reminder that zonal and seed geraniums, American marigold, and all types of impatiens are susceptible to iron/manganese toxicity, a nutritional disorder associated with low growing medium pH. This problem is sometimes called "bronze speckle" due to the appearance of numerous small brown spots on the edges of the leaves of geranium and marigold. The target pH range to prevent toxicity is 5.8-6.5.   If the pH is lower than the target range the risk for toxicity increases because at low pH too much iron and manganese becomes available to these plants.

Over fertilization and Soluble Salts Injury on Mums

Providing adequate fertility is important in maintaining optimum plant growth in mums. However over-fertilization can result in high concentrations of soluble salts that can cause injury to the plants. Chrysanthemums are among a number of plant species known to have susceptibility to soluble salts injury. Over-fertilization results in high concentrations of soluble salts in the medium. As the salts are translocated throughout the plant they accumulate at the leaf tip and margins and when they reach toxic levels they cause “salt burn”.

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