Pour-thru on Primula
During a recent grower visit, I noticed several primula
plants that had begun to develop chlorotic foliage. I asked the grower if they
had recently conducted a pH analysis of the substrate and they indicated they
had not. Primula is similar to many other iron-inefficient plants, it that iron
becomes insoluble and thus unavailable for uptake by the roots due to high substrate
pH. This is not to be mistaken for flower bud initiation, where recently unfolded
leaves of some cultivars develop a pale green color. The recommended pH range
for primula is between 5.5 to 6.0. After a pour through test, we determined
that the pH was 6.3. This grower can use one of several options to lower their
substrate pH. These options are detailed in the January 2018 e-GRO Alert: Volume
7 Number 2.
High substrate pH (>6.2) will result in iron deficiency
symptoms that appear as chlorosis of recently unfolded leaves. Advanced symptoms
of iron deficiency can result in completely bleached leaves.
Low pH (<5.5) can result in zinc toxicity
that appears as necrosis on the edges of older leaves.
Roberto LopezAssociate Professor and Floriculture/Controlled Environment Extension Specialist, Michigan State University
Roberto G. Lopez is an Associate Professor and Floriculture/Controlled Environment Extension Specialist at Michigan State University. He has an appointment in research, teaching and extension. His area of expertise is; controlled environment specialty crop production; Lighting applications for greenhouses and indoor vertical production; light-emitting diodes; young plant propagation.