Healthy greenhouse and nursery plant stock sells. Conversely, a plant with yellow or wilted leaves typically discourages customers from making a purchase.

Raising healthy stock begins with understanding and successfully managing factors that contribute to plant damage. “Is it a nutrient disorder or a pest or disease?” asked Neil Mattson, Associate Professor and Floriculture Extension Specialist at Cornell University Department of Horticulture in Ithaca, New York.

Though symptoms of damage by pests or disease look similar to nutrient disorders, there are distinguishing characteristics. The first step in diagnosing and correcting nutrient deficiencies in greenhouse or nursery stock begins with proper identification.

“Watch for patterns,” he added. “Pests and diseases cause spotty damage that are not consistent throughout the crop.” Damage caused by nutrient imbalance is symmetrical and consistent throughout the entire crop.

Understanding plant nutrients

Plant nutrients are grouped into one of two classifications: mobile or immobile nutrients. A plant-mobile nutrient can be moved from one area of the plant to another. For example, mobile nutrients can be shifted away from older, established leaves to support tender, new growth. Nitrogen (N), phosphorous (P) and potassium (K) are examples of mobile elements. Plants deficient in mobile nutrients exhibit signs of stress in the oldest (lowest) plant growth first.

Conversely, plant-immobile nutrients cannot be shifted from one area of the plant to another. They are in essence “stuck” where they first land in the plant. Boron (B), calcium (Ca), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn) are all plant-immobile nutrients. When plants are deficient in any of these elements, yellow begins on the newest (upper most) plant growth.

In addition to the nutrient characteristics, several factors contribute to nutrient deficiency. Other nutrients present in the soil and media, soil pH levels, nutrient imbalances, poor root systems and temperatures all can contribute to a nutrient imbalance.

There are five nutrient deficiencies that occur most often in greenhouse and nursery operations. This article will explain three common deficiencies, tips for identification and guidelines for correction.

Nitrogen deficiency

Nitrogen deficiency may be the most common nutrient disorder among greenhouse and nursery producers. Since N is classified as a mobile nutrient, signs of stress will first appear in the oldest (lowest) section of the plant.

“The old leaves are affected first and uniformly turn light green and then yellow,” Mattson said. The leaves of a nitrogen-deficient plant may also be smaller in size and may prematurely drop off the plant. “The plants are stunted and have reduced root growth and branching,” he added.

Correcting nitrogen deficiencies in field-grown nursery stock begins with a pre-plant nitrogen test and is a multi-year process. Mattson recommends applying 50 pounds per acre (approximately 0.5 ounces per plant) prior to bud swell in the first year.

In the second and subsequent years, he suggests 80 to 120 pounds per acre per year. “Apply two-thirds prior to bud swell and one-third in early June,” he said. Halt nitrogen applications after July 1 to reduce chances of late growth injury from winter conditions.

Band the applications at least 8 to 10 inches from the stem or apply through an irrigation system. Since nitrogen is water soluble, it is okay to use soil surface applications.

Balancing nitrogen deficiencies in container plants is a bit different than field grown stock. First, “verify the fertilizer injector is working,” he said, “then increase the fertilizer rate with a complete water soluble liquid fertilizer.” The plants can also be top-dressed with controlled-release fertilizer for longer-lasting control.

Phosphorus deficiency

Severely stunted plant growth and deeper-than-normal green foliage indicate phosphorus deficiency. In some plant species, the older plant leaves may even turn purple.

“Cool temperatures, for example less than 55 degrees, can cause inactivity of roots, which leads to phosphorus deficiency,” Mattson said. Most commonly, this is seen in field nursery crops and the symptoms are usually just attributed to the cold spring weather.

For field grown plants, it’s important to start with a pre-plant phosphorus test. Testing is important as phosphorus rates vary by crop and density. If the results indicate additional phosphorus is needed, apply at 44 pounds P/acre or 100 pounds per acre P205.

“Triple superphosphate (0-46-0), monoammonium phosphate (11-52-0) or diammonium phosphate (18-46-0) are all good options,” he said. Because phosphorus is not a mobile element, broadcast apply and then incorporate it into the soil. “Often it is not required in field soils after establishment,” he noted.

To adjust phosphorus levels in greenhouse crops first check that the injector is working. Then, if a moderate P fertilizer like 20-10-20 is being used, it can be increased to a higher P fertilizer such as 20-20-20. Top-dressing with a controlled release fertilizer with P like a 15-9-12 provides longer-term control. Increasing the greenhouse temperature can also help. “Plants recover quickly as root-zone temperatures warm-up,” he said.

Magnesium deficiency

Whereas plants affected by magnesium deficiency begin to yellow in older leaves first, the pattern will look different than that seen in other nutrient deficiencies. “The veins stay green, the yellow begins at leaf edges and then work inward,” he said. “That’s called interveinal chlorosis.”

When the soil pH that is less than 5.5 the uptake of magnesium is reduced and leads to a nutrient deficiency in the plant. Pay attention to the soil pH before planting stock to avoid magnesium deficiencies. “Dolomitic limestone can be used to raise pH,” Mattson said. “It includes both calcium and magnesium.” Strive to apply 30 to 100 ppm or 60 to 200 pounds per acre. “If magnesium is needed in the soil, but lime is noted, incorporate or drench with Epsom salts (MgSO4),” he said.

Container plants apply 2 ounces per 100 gallons of magnesium sulfate (Epsom salts) in a constant liquid feed program. “Eight ounces per 100 gallons as a single application can be applied once a month or switch to a water soluble fertilizer like 15-5-15 that contains magnesium,” he said.

More to learn

Diagnosing and solving nutrient disorders in your greenhouse and or nursery plant stock is key to running a profitable operation. There are two remaining deficiencies – iron and manganese – that are commonly found in greenhouse and nursery stock. In next month’s issue, look for a detailed explanation of both as well as recommendations for correcting soils to achieve healthy plant growth.