chlorotic clematis

(Question)

in North Toronto, sun, medium moisture, along a fence, amended with garden compost
I have 3 clematis on a fence and one freestanding that have quite yellow leaves towards base and green ones at growing tip (photo enclosed). I figure there is a soil deficiency but what?

 

 

(Answer)

Thank you for your inquiry. Chlorosis or the yellowing of leaves is defined as a lower than normal amount of chlorophyll.

Depending on where the chlorosis is located; over the entire leaf, between the veins, young leaves or older leaves will give a hint as to what macro or micronutrient is lacking in the soil. From your photo it appears that you have interveinal chlorosis; this is when the leaves are yellow but the veins remain green. A lack of iron in the soil is usually the cause of interveinal chlorosis, however a number of other soil issues can also be the culprit. Manganese deficiency, a high soil pH, zinc deficiency, wet soil conditions, compacted soil, high organic content in soil, high salts, high levels of phosphorus, copper, or zinc can all  produce the same symptoms.

In order to determine if the interveinal chlorosis is a result of iron deficiency you can purchase chelated iron from your local garden centre. Follow the directions on the package and you should notice green-up within 2-7 days.

If you do not notice a difference within a week it could be that your soil has a high pH, or a high phosphorous level. Phosphorus is an important element in the  flower and seed producing  systems and is  required for primary root growth. The disadvantage to phosphorous is that it has a slow solubility. It can build up in soil and as a result, the micronutrients can be bound up so tightly  that they are not readily available to your plants. If this is the case you may wish to have your soil tested. Click  here to read the step by step process in City of Toronto’s Guide for Soil Testing in Urban Gardens.

Click here to read an excellent article by the  Missouri Botanical Garden on Soil Fertility and Fertilizer

Good Luck.