Photo: Foliar iron deficiency on river birch
River birch (Betula nigra) is a popular landscape tree in the Southern Appalachian region (USDA zones 6-7). The cultivars 'Heritage' and 'Duraheat' have made a good native species even better with resistance to aphid and leafhopper insects. However, river birch demands a soil pH which is moderately acid. Why?
Iron is an important minor nutrient element. If the soil pH rises (becomes less acidic), available iron becomes less available to plants. Major landscape trees also affected by "pH nutrient creep" include favorites as pin oak, willow oak, sweetgum and littleleaf linden. An old timey recommendation was putting several nails in the bottom of the hole at planting time.
Modern day solutions include: 1. adding elemental sulfur in late fall to lower the pH and next year's new foliage should stay green all summer long; OR 2. apply iron supplying fertilizers like Ironite® or Sequestrene®, following package rates accurately; OR 3. feeding acid raising soluble fertilizers like Miracid™ or Hollytone® which contain iron.
Follow any one of these three approaches and summer color will gradually return this summer or next.