Lawanda's Garden

For the past few years, the leaves on the tips of the stems of my rose bush have leafed out a much lighter green than the leaves on the lower parts of the stems.  The veins of the leaves remain dark green though.  Soon those leaves  top leaves turn yellow and then the edges get brown

            I admit I have difficulty identifying plant nutrient deficiencies, especially when it comes to the micronutrients, which are those nutrients other than the big three – nitrogen, phosphorus and potassium – that are found in most commercial fertilizers.  The problem is that the symptoms of many nutrient deficiencies look alike. 

For example, interveinal chlorosis, the yellowing of tissue between leaf veins while the veins remain green, can be the result of a lack of magnesium, iron, manganese, zinc or boron. 

            There are other clues however, that can pinpoint the problem.  One of the easiest is to determine whether the problem is occurring on older, lower leaves or on younger, upper leaves.  In the list above, symptoms of magnesium and zinc deficiencies occur on older leaves and the others appear on younger leaves. 

            Say the problem is on older leaves.  Besides interveinal chlorosis, both magnesium and zinc defiencies cause stunted growth, so that doesn’t narrow the problem down any.  But zinc deficiency also causes leaves to be thickened while magnesium deficiency does not.

            Along with interveinal chlorosis on younger leaves, iron deficiency causes stunted growth.  A lack of boron produces twisted and pale green young leaves and buds may die and a plant with a deficiency of manganese will have brown spots scattered throughout the leaves.

            There is a further twist to the problem though.  After going to the trouble of determining the problem and trekking to the garden shop to buy a bag or bottle of some potion that’s going to fix it, you may be wasting your time and money if your soil pH is not at the correct level for the nutrient to be taken up by the plant. 

I determined that the problem with my rose bush was an iron deficiency, but I learned that iron deficiency is actually rare in soils, and that the problem might be that the pH of my soil was too high.  A high pH ties up the iron in soils and makes it unavailable to plants.  To lower the pH, I sprinkled a few cups of coffee grounds around the rose bush.  In a few weeks it looked a lot healthier.  With all the rain we’ve had, I’ll be adding more coffee grounds again soon and I’ll make a note on my calendar to do it again early next spring before the rose bush even begins to leaf out.

To prevent deficiencies in micro-nutrients in the first place, generous use of compost and foliar feeding with liquid seaweed or fish emulsion should do the trick.