Have you ever read or heard that you should be “…adding lime to the location your clematis is planted in.”? Just as with the old axiom, “plant their heads in the sun and their feet in the shade”, I’m here to tell you that this is another one of those urban legends being spread about.
In my article, FYI on Soil pH, I discussed the importance of pH and suggested to you that the correct pH would be one on the acidic side of the scale. So, if you are indiscriminately adding 1 cup of lime to each of your clematis once a year or giving them a regular light dusting without having the soil professionally tested, you can actually be putting them at risk. This is because you will be increasing the soil’s pH (i.e. making it alkaline) which means they may not be able to uptake required nutrients.
If you are one of those who believer that your clematis require an alkaline condition, it may interest you to know that Roseville Farms, which is a North American clematis specialist nursery that grows over 4 million annually, is growing their liners and plugs in a pH between 5.5 and 6.5, which is strongly acidic to slightly acidic (Source: Roseville Farms Wholesaler Growers FAQ).
Also, another one of the world’s largest producers of clematis, Guernsey Clematis Nursery Ltd., has been using a pH averaging 5.5 (strongly acidic) in the production of their container plants. (Source: page 65 of Clematis For Everyone by Raymond Evison).
Paul Pilon is a horticultural consultant and researcher who authored Perennial Solutions: A Growers Guide to Perennial Production, which is a reference book for wholesale growers in the horticultural industry. He wrote an article for Greenhouse Product News titled: Clematis INSPIRATION. In it he describes how to grow clematis professionally in a greenhouse. He wrote that this particular clematis requires that the pH be maintained at 5.7-6.4 (moderately acid to slightly acid), but I will surmise he also meant other clematis as well.
What is interesting to me is that Mr. Pilon, along with these major professional growers who are involved in today’s clematis production, all agree that clematis are not alkaline lovers. In fact, when one considers their pH recommendations of maintaining a pH from 5.5 to 6.5 in their production, the implication is quite clear that clematis are acid lovers.
For the record here are two more opinions about the myth of adding lime:
In 1989, Christopher Lloyd, who was a definitely a clematarian ahead of his time because he was one of the first to challenge notion of adding lime. In his book was published in 1998 and titled Clematis he wrote:
“The commonest misconception is that clematis need providing with lime if none is present in the soil. Let me assure you straight away that this is quite unnecessary (unless your soil is so acidic that it needs extra lime for everything you grow, and this is rare in British gardens). There is no need to go scrounging with your bucket for mortar rubble out of old buildings. All the same, you will still read in many books and articles on clematis that lime is a prerequisite. I have no doubt that this notion arose from the fact that our native clematis, C. vitalba, is most often found wild on chalk or limestone. One swallow doesn’t make a summer. C. vitalba has sired only one hybrid grown in gardens. And anyway itself will grow perfectly well in acid soil if you ask it to. So will all the rest. I remember Miles Hadfield telling of the large collection of clematis in his parents’ garden in Birmingham (and indeed I remember an ancient C. armandii on a wall of their house) where the soil was excessively acid on account of being impregnated by sulphurous industrial fumes. But the clematis flourished exceedingly. This may also, I suspect, be linked with the fact that they got less wilt disease, because the sulphur dioxide in the air acts as a fungicide...
The disadvantages of adding lime to the soil where you grow a mixed collection of plants are clear. It won’t hurt the clematis but it will make the rhododendrons, camellias and most heathers difficult or impossible to grow, all of them excellent host plants for clematis to clamber over, and there are many more that are similarly calcifuge.”
In 2005, the renowned clematarian Dr. John Howells, wrote a technical article for the International Clematis Society’s yearly journal. In They Say Clematis Are Lime Lovers, he discusses the authorities in the past who believed that a limey or chalky soil was essential in order to grow clematis in the garden. In his conclusion he writes: “The support given by authorities for the notion that clematis are lime lovers is considerable and impressive. But they all have a weakness in common – their views are not based on systematic study.” He does not draw any conclusions about who is right or who is wrong and adds that: “The need is for systematic study.”
The following year he followed up the discussion with another article, Clematis are Acidity Lovers, where he presents five trials he conducted (he apparently undertook his own systematic study) with various clematis to ascertain the effect of soil pH on their wellbeing. From these comprehensive studies he concluded that clematis will grow well in acid soils. The lesson learned here is that clematis will flourish in a pH of 5.0 and above, but will perish in a pH of 4.0 and below.
I hope that this article will alert those of you who are adding lime to your clematis that it is clearly not a “sweet” treat for your clematis. After all, it is my goal to give my visitors a positive experience when growing clematis. I would hate to imagine that you are not receiving all the beautiful blooms that your clematis has to offer you just because you are clinging to an old, unfounded belief that could do more harm than good. So, next time you get out that bag of lime, think twice before torturing your clematis with its contents, because in the Clematis Queen’s kingdom, the offender should be punished by guillotine (don’t you agree?).