Mineral deficiences in plants

In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green colour of leaves, chlorotic leaves are pale, yellow, or yellow-white.

The affected plant has little or no ability to manufacture carbohydrates through photosynthesis and in extreme cases may die unless the cause of its chlorophyll insufficiency is treated. Specific nutrient deficiencies (often aggravated by high soil pH) produce chlorosis, which may be corrected by supplemental feedings of missing compounds in various combinations. Different mineral deficiencies act in subtly different ways.

Deficiency of Nitrogen (N)
The characteristic deficiency symptom of nitrogen is the appearance of uniform yellowing of leaves including the veins, this being more pronounced on older leaves. The leaves become stiff and erect. If the condition of nitrogen stress persists, then the result is decreased foliage and shoot growth.

Conditions inducing Nitrogen deficiency include heavy rain causing leeching, low organic matter content of soils, denitrifcation (losses of N2 and N2O to the atmosphere).

Deficiency of Magnesium (Mg)
Magnesium deficiency causes yellowing, but differs from that of nitrogen. The yellowing takes place in between veins of older leaves and veins remain green, this is followed by necrosis (unnatural death) of tissues. Interestingly, Mg deficiency may be induced in tomatoes by high levels of ammonium in the nutrient solution (Kafkafi et al., 1971).

Deficiency of Iron (Fe)
The principal veins remain conspicuously green and the surrounding portion of the younger leaves turn yellow. Conditions inducing Iron deficiency include calcarous soils, soils high in P, Mn, Cu, or Zn, high rate of liming.

Deficiency of Potassium (K)
Under potassium stress condition, the yellowing of leaves starts from the tips or margins of leaves extending towards the center of leaf base. The yellowing is interveinal and these yellow parts become necrotic (dead spots) with leaf curling.

These are some of the more common causes of mineral deficiency, and as there are many more minerals making a contribution to the Cannas growth, then we can see that these are the first causes that should be investigated when chlorosis is spotted on foliage.

What is the best way to overcome these Environmental deficiences? Well, that is obviously to deliver the missing minerals to the chlorotic plant. The best immediate source of trace minerals is a liquid feed with seaweed fertilizer. However, that is only a temporary fix, as the basic soil deficiency has to be corrected by introducing the missing element(s).

And what happens if there is no improvement from the upgraded feeding regime? Then it is now time to think the worst and start considering the possibility of chlorosis induced by Canna virus, more of which later.

Sea sunshine loved by Cannas

The photograph above shows foliage from a single Canna plant. The story behind it was revealed in a recent posting on the International Canna Club on Yahoo, when Bernard Yorke from Australia wrote in to explain that he wanted to pass on details of his results with Seasol on a sick looking plant. He had a batch of Cannas in an old dried out part of the garden, these were the ones that he had been meaning to dig out and destroy on account of virus like symptoms.

Mr Yorke stated that, "I had been having some aphids under the surface in a few spots, particularly where the soil was more open, so it was recommended I spray with Rogor 100 (not rogor 40, this systemic one is stronger) and at the last minute I laced the mixture with some Seasol. In 3 weeks I had noticed a considerable difference, in fact old plants had enormous growth from the base, they had whole batches of new shoots and leaves. Needless to say, I did the same spray 3 weeks later".

The attached shows the result, obviously the leaf on the left is one of the old leaves, the two on the right are much stronger.

On reading the label on Seasol, I see that it promotes good growth and helps the plant fight against viruses. Note it doesn't 'cure'. Anyway, I have old plants with a whole new lease on life and I am watching them most closely in future. The Curator of our gardens here tells me that Seasol is a wonder fertilizer, good to get rid of caterpillars and the like as well.

Just thought this may be of interest. I find Seasol also beneficial in soaking bulbs before planting out."

My own take on this is very simple, possibly pseudo-science.

This is a sea-weed based, organic fertilizer. (The name is a conjuncture of "Sea" and "Sol", the French word for sun). There are, I hope that I remember my biology right, 72 bio-minerals, i.e. plant nutrients. Most have been leeched out of the soil over the millions of years that the earth has been exposed. However, they are still in suspension in the sea, and sea weed contains traces of all of these nutrients. The application of a seaweed based fertilizer is one way to ensure that our Cannas get everything that they would otherwise lack.

Fertilizers typically provide, in varying proportions, the three major plant nutrients (nitrogen, phosphorus, and potassium), the secondary plant nutrients (calcium, sulfur, magnesium), and sometimes trace elements (or micro nutrients) with a role in plant nutrition: boron, chlorine, manganese, iron, zinc, copper, and molybdenum. It is those last seven micro nutrients that are present in sea-weed, but not in most cheaper commercial fertilizers.

Now, if virus is still present can only be determined in a laboratory, but if all my foliage looked like the ones on the right of Bernard's photograph, then I would never complain.

I have identified that "Mr Fothergill" is the UK representative for "Seasol", and I have already identified my local UK supplier. Now we have to try it out and see what happens.

Seasol web site
Cannas by Bernard Yorke