Lime-Loving Plants… Do You Know Them?

My first experience with the magic which can be performed by the addition of lime to the soil came when I transformed a bed of sweet sultans from sickly plants to vigorous specimens with blossoms of exhibition quality.
In common with most beginners I wanted to have outstanding success with one certain flower. In my case it was the sweet sultan Centaurea moschata (Centaurea suaveolens), but if they flowered at all for me the blossoms were small and the stems weak and crooked.

Simple Secret To Success

The secret of success was so simple that I blush to mention my repeated failures. I learned that the centaureas as a family are lime-lovers, and when I worked finely broken plaster rubble into the bed of sweet sultans the crop of cut flowers rivaled the florist’s finest, tallest plants were 51 inches in height and bushy, the long-stemmed blossoms huge and the colors particularly bright.

flowering campanula an Alkaline loving plant

My next revelation of the magic properties of lime gave spectacular results with so little effort aroused my interest to the point of obsession.

I found that although experiments to ascertain the degree of soil acidity certain plants require have been given wide publicity, information about the effects of lime in the soil has not been well disseminated. My accumulation of notes on the subject certainly provides facts enough to justify the use of lime as sound working practice rather than mere theory.

Lime – A Farmers Secret Sauce

Farmers and market gardeners find it profitable practice, for they know that many field and vegetable crops produce a consistently higher yield on well-limed soils. Liming becomes absolutely necessary for most vegetables where the soil is inclined to be acid.

Legumes usually require an alkaline soil, and soybeans, squash, asparagus, canteloupe, cauliflower, onions, parsnips and rhubarb appreciate extra lime in the soil.

Generations of adaption to various environments have conditioned most of these are known as calciphobes. Where our favorite ornamentals to a neutral soil, although carnations, gypsophila, delphiniums, mignonette, nasturtiums, sweet peas and many others prefer sweet soil.

When plants are brought from high mountain ranges, deserts, plains, jungles or any specialized environment, they lack the ability to conform to the soil difference which, has been developed through centuries by our garden hybrids.

The difficulty, and expense involved obtaining these plants makes it imperative to ascertain their special requirements, then to duplicate these as closely as possible in the garden.

Of recent years this process is usually undertaken with the greatest consideration regarding the acid soil group; but with less understanding where lime-loving plants are concerned. It would be just as reasonable to hope that those plants requiring an-extremely low pH will thrive in neutral soil as it is to expect that plants native to a strongly neutrality.

Natural Habitat

The best way to determine Soil preference in plants is by reference to their native habitat. Plants from the high Sierras, Rocky Mountains or any other granite range, will not tolerate lime in any form. But many other plants from the western plains are lime-tolerant if not definitely calciphilous.

A lime deficiency is now considered the main cause of their frequent poor growth in many eastern gardens. A great number of Plants from the limestone range would seem; on first thought, to require straight acid soil treatment.

But further investigation will often prove that while the plant seemingly grows in leafmold; the long taproot strikes deep into the crevices of the limestone formation below the humus of the surface soil.

Lime Lovers Divide Plant Families

The fact that many, flower families are divided among themselves makes it even more important to consider the native haunts of the species in question. Plant explorers and many of our nurserymen designate the locale and often the formation found beneath the plants under discussion.

This is often the key to their culture. Soil above marble, limestone and serpentine is almost certain to be alkaline, while that above quartz, granite and mica is usually acid. Acidity generally prevails above sandstone and shale, although it may be neutral or even mildly alkaline.

Alkalinity A Deadly Poison

Where acid soils occur in nature we find a class of plants to which the least taint of alkalinity is a deadly poison; these are known as calcipphobes. Where the soil is alkaline the lime-lovers, or calciphiles, are found. These plants seemingly depend on the action of lime for the release of nutrients in the forms most easily assimilable by their roots.

This it does by altering the mineral compounds present in the soil to the essential elements required for the growth. it must be remembered that lime is not a fertilizer and is to be used only as an amendment to improve the texture and change the chemical, by which process, also activity of the beneficial soil bacteria is greatly increased.

When it has been determined that the plant in question requires increased alkalinity, the next step is to decide in which form it is best to provide it. Many rock plants are happiest with a top dressing of limestone chips.

These also serve to protect the crown of the plant from undue dampness and the blossoms from being spattered with mud. Old mortar rubble may be used as a top dressing or dug into the soil, the degree of pulverization depending on the plant and the location. Coarse pieces used in the root run will help to improve drainage and also most nearly simulate the stone calcareous range where limestone is unavailable.

In garden beds and for field crops it is obviously better to use hydrated or agricultural lime, the proportion depending on the acidity of the soil and the nature of the proposed planting, or ground limestone which can safely be used in large quantities with an alkaline reaction such as bonemeal and superphosphate without its usual gypsum content may be used to advantage.

Frequency of Lime Application

Lime should not be needed oftener that every two years. The alkaline reaction may continue for as long as five years or indefinitely, depending of the type of soil. Because of the constant leaching, sandy soil, derived form the granite and naturally inclining toward acidity, requires lime as well as fertilizers at more frequent intervals than close, fine-textured soil derived from limestone.

Glacial soils, silts and loss deposited by wind will need constant attention, while a sedimentary soil of alkaline reaction may never need amendment except for the accommodation of acid-loving plants.

It has become common practice in landscape design to provide for acid soil stations. Some provision for segregation of calciphilous plants is also desirable.

Where such a grouping of plants is impossible, as in established plantings, the soil preferences of surrounding plants must be determined before lime or fertilizers of alkaline reaction are added to the soil. The importance of this step cannot be overemphasized, as lime is an immediate and deadly poison to the acid-lovers and will do irreparable damage if allowed to seep into their root zone.

The idea of establishing alkaline soil stations may seem far-fetched, but will surely appeal to the serious gardener as an easy way to get the best performance from this class of plants without damage to others.

In the rock garden and perennial borders the sunny, open spaces might be designated as alkaline stations, as the lime-lovers. broadly speaking, are sun-lovers and the acid soil plants require shade. There are exceptions to this rule in both growth which should be confirmed with respect to local conditions such as altitude, humidity, summer temperatures, etc.

In certain regions the soil type is so well known as to eliminate need for testing, except for culture of those plants requiring a precise pH. In other localities both acid and alkaline soils are found in a small area, oftentimes within the same garden.

The sandy soil of my old home where I gardened for 15 years was inclined to be acid. The water was soft, the water table row and the soil loose and perfectly drained. The new garden, not three miles away, has sweet soil with hard water at a high level and the drainage is poor.

Lime Preferred

Violets also flourish here. I suffered a heavy loss on moving into the new garden when all my violet hybrids were thoughtlessly placed in an acid-soil bed. It did not take them long to die.

Their preference for a sweet soil is undoubtedly the reason why violet growers give as a cultural tip the rather ambiguous advice that violets should not be planted under pine or redwood trees.

These directions apply only to varieties of the sweet violet, Viola odorata, as most species require acid soil, although limestone chips are recommended in any compost prepared for V. alpina and V. pedatifida.

Among, rock plants we find few families in which the members are unanimous in their needs. In almost every large genus there are species as equally insistent in their lime hatred as the related calciphilous species are in their demand for it. All achilleas and aethionemas are believed to need lime and the dianthus family is in almost complete accord.

Schizanthus, when grown in pots, should have a handful of finely pulverized mortar rubble to each pot. Gloxinias will also make a finer growth in sweetened soil. The lovely prairie gentian (eustoma) needs lime in the seed compost as well as a strongly alkaline growing medium.

An Alkaline Diet

All the border campanulas thrive in a limy soil, as well as many of the rockery species. Clematis as a family demand a well-limed soil, exceptions being C. verticillaris and C. crispa which require a pH of 5 to 6.

Scabiosa caucasica and its numerous beautiful varieties cannot be expected to thrive in an acid soil. Recalcitrant stock plants can often be coaxed to bloom by an application of lime as a top dressing, and the thrifty growth of wallflowers in alkaline soil is evidence that lime in some form is a requisite.

Generations ago gardeners realized that bearded iris made their best growth in a sweet soil, with consequent heavy liming the accepted procedure in preparation of iris beds.


This practice quickly fell into disfavor when it was discovered that the lush growth induced by the application of lime rendered the iris more vulnerable to attack by fungus diseases. This does not mean, however, that an acid soil is preferable or that an alkaline soil is not the finest medium for their cultivation, but only that lime should not be used to force a soft, spongy growth which may have less immunity to disease.

A few of the trees which thrive in an alkaline soil are the casuarina, catalpa, yellow locust, hickory and walnut. Among the evergreens are red cedar, juniper and the yew, the chalk soils of England boasting noble specimens of its finest development.

Just as the best results are obtained from acid-loving plants when special consideration is given the soil, lime-lovers, too, should be given the conditions they like. An application of lime to calciphilous plants will do wonders if they are growing on acid soil.

by L. McCombs

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