Mineral deficiencies in plants (Boron, Iron, Magnesium, Manganese)

Recently, I had to do some research for a client regarding a possible mineral deficiency in her Cotinus coggygria - Smoke Tree 'Golden Spirit'.  A year after installation and with good rains and warmer weather, these plants still don't seem to be adapting very well to their new environment.

After double checking that the irrigation was working correctly I then thought it might be a fungal infection but then it occurred to me that it is actually more likely to be a mineral deficiency in the soil.

During my research I learned that mineral deficiencies can look just like the symptoms I was seeing on the Smoke Tree shown above. Specifically Boron, Magnesium and Manganese deficiencies.

Magnesium Deficiency

Magnesium (Mg) has an important role in photosynthesis because it forms the central atom of chlorophyll. Therefore, without sufficient amounts of magnesium, plants begin to degrade the chlorophyll in the older leaves. This causes the main symptom of magnesium deficiency, chlorosis, or yellowing between leaf veins, while the veins stay green, giving the leaves a marbled appearance. Due to the mobile nature of Mg, the plant will first break down chlorophyll in older leaves and transport the Mg to younger leaves which have greater photosynthetic needs. Therefore, the first sign of magnesium deficiency is the chlorosis of older leaves which progresses to the young leaves as the deficiency continues but the leaves don't turn brown or necrotic unless the deficiency is extreme. 

Iron (Fe) deficiency appears very similar to Magnesium deficiency but the yellowing begins in the younger leaves instead of the older leaves (more difficult to diagnose in a tree with naturally yellow young leaves such as the Cotinus in the top photo).

Boron & Manganese Deficiency

Manganese (Mn) deficiency is often caused by over liming which is a common problem in lawn trees otherwise it is most often found in peaty and sandy soils with a high pH (alkaline). Symptoms are similar to iron deficiency which include leaves turning yellow or brown between the veins but the smaller veins remain green creating a 'fishbone' or 'checkered' effect. Chlorotic and necrotic spotting are common symptoms resulting in premature leaf drop or delayed maturity in some species. 

Adding sulphur to the soil - which will increase the acidity (decreasing pH) - will help solve the problem. I personally have found adding diluted white vinegar (1 tbs/ 1 gallon of water) also helps to lower pH (acidify the soil).

The symptoms of boron (B) deficiency are poor development of the growing tips of the plant and bushy stunted growth. It is more likely in soils with pH above 6.5 or over-leached sandy soil. Boron is necessary for calcium to perform its functions in the plant but too much boron is also harmful to the plant. Excess use of magnesium sulphate will also cause a boron imbalance. 


For the best diagnosis, lab tests of the leaves and soil are necessary which can often be done through your local Farm Bureau. Apart from testing, checking the type of soil, how much watering is being done, the water itself (ie - Southern California water has high salt, chemical and dissolved particulate content especially in the summer) and of course the symptoms on the leaves. With this information, a reasonable informed decision can be made about which course of action to take.


Here are some great sources of information:

http://www.phoenixtropicals.com/vitaminNutrientDeficiencySymptomsPlants.html

http://en.wikipedia.org/wiki/Magnesium_deficiency_(agriculture)

http://www.caes.uga.edu/publications/pubDetail.cfm?pk_id=7723

http://www.allotment.org.uk/fertilizer/trace-elements-plant-nutrition.php

http://en.wikipedia.org/wiki/Boron_deficiency_(plant_disorder)

http://edis.ifas.ufl.edu/ep362