The iron and manganese deficiencies are commonly found in greenhouse and nursery stock. In severe cases of iron deficiency, the entire plant leaf turns yellow and the edges of the leaf scorch turn brown. Interveinal chlorosis appears first on the young leaves and, as the deficiency increases, it can spread to older leaves, too. Plants like silver maple, river birch, pin oak, sweetgum, dawn redwood, berries and grapes are extremely susceptible to iron deficiencies. Most fruit trees, conifers and shrubs are moderately susceptible as are London planetree, mountain ash, most maples, magnolia, horse chestnut, birch (Betula species), beech and aspen.

Managing pH levels is key to limiting iron deficiencies. In the greenhouse, it is recommended that crops are grouped together based on pH requirements. Using information provided by Cari Peters, manager of research and analytical services at J.R. Peters Group, and Neil Mattson, assistant professor/floriculture extension specialist at Cornell University, recommends:

The “low” pH group prefers growing media between 5.4 and 5.8 pH. Plants that are prone to iron, boron and other micronutrient deficiencies include the following:

  • Bacopa
  • Begonia
  • Bracteantha
  • Calibrachoa
  • Diascia
  • Nemesia
  • Pansy
  • Petunia
  • Snapdragon
  • Tiarella
  • Sutera
  • Verbena
  • Vinca
  • Zinnia

The “medium” pH group prefers growing media between 5.8 and 6.2 pH. Plants that are not particularly prone to micronutrient deficiencies include the following:

  • Angelonia
  • Ageratum
  • Bracteantha
  • Chrysanthemum
  • Coleus
  • Dahlia
  • Euphorbia
  • Fuchsia
  • Impatiens
  • Lobelia
  • Oxalis
  • Poinsettia
  • Primula
  • Torenia
  • Osteospermum

The “high” pH group prefers growing media between 6.2 and 6.8 pH. Plants that can be prone to iron and and other micronutrient toxicities include the following:

    • Alocasia
    • Aloe
    • Begonia-Rex
    • Calendula
    • Cleome
    • Cyclamen
    • Dianthus
    • Geranium
    • Heliotrope
    • Marigold
    • New Guinea Impatiens
    • Pentas
    • Perilla
    • Portulaca

Zonal and seed

Maintaining long-term solutions to correcting iron deficiencies in the field includes low soil pH. Start with site selection and preparation. “Incorporation/drenches of iron sulfate if soil pH is low enough (less than 6) and drenches with iron chelate if the soil pH is high,” he said. A quick, but temporary solution includes a foliar application of iron sulfate or iron chelate for a quick green-up of affected plants. Stem injections for landscape plantings last longer than foliar iron applications, but does not solve underlying problems of high pH.

Katie Navarra is a freelance contributor based in Clifton Park, New York, and writes about agriculture and the equine industry regularly.