Root pruning

Root-pruning has two distinct, and opposite purposes. In some cases (let's call it root-trimming) it is intended to provoke the growth of new feeder roots, which can stimulate a plant into growth. In the other cases it is meant to check the growth of the plant to encourage flowering. In these latter cases, root-pruning accomplishes much the same restriction on growth as allowing the plant to become root-bound. Trimming the small roots to encourage the growth of feeder roots is stimulating. Cutting back the larger roots will reduce the total mass of feeders the plant can produce.

WR: White Lilacs for Winter (1868)
"The plants that are intended for forcing are cut round with a spade in September, to induce them to form flower-buds freely; and they commence to force early in the autumn."

Nicolas: Root-Pruning Roses (1935)
Since feeding-roots generally are annual and partly disappear, to renew themselves each year, most of the old fibers on the dormant plant received from the nursery are useless, and the first function of the plant is to grow new fibrous or feeding-roots. The process of shortening the heavy roots is to promote and accelerate the growth of fibrous and feeding-roots; each root, after a fashion, becomes a "cutting" by itself.

Collins: Avocado (1905)
The tree flourishes in many localities where it fails to bear fruit, and, as with the mango, this sterility is usually found in localities of almost continuous humidity. Under such conditions an artificial check, such as root pruning, has been found to induce flowering and the setting of fruit.

House Beautiful 10(2): 81 (July 1901)
Plants for the Terrace by Ida D Bennett
Hibiscus. In spite of the florist's claims to the contrary, I do not consider the hibiscus a good bedder. A good summer bloomer it certainly is, but it does better in pots sunk in the ground or in the sand box, where it can be kept moist and will receive the morning sun. In the open ground the tendency to excessive root-growth interferes with its blooming. The hibiscus blooms well when root-bound, but must never be allowed to dry out during the blossoming period, as this is the cause of the dropping of the buds so much complained of. When plants are wanted for winter blooming, bedding out in the spring and lifting in the fall may be wise, as the plants will be in better shape for the winter blooming than if grown in pots and allowed to bloom during summer.
     In the house the excessive root-growth of the hibiscus may be pruned if it threatens to require too large a pot. To accomplish this with the best results and the least trouble, I run a knife down through the soil on each side of the pot, slicing off a good half of the roots. The remaining roots will quickly branch out into many new feeding roots—the life of the plant—which will result in an early crop of flowers. This will often bring a backward plant into bloom, and the habit of blooming once established the plants will be found very reliable bloomers.

The Garden: Root-Pruning (1892)
The value and necessity of root are not understood and recognised in the way should be and few people are aware of the effects it has on trees, especially such as are heavy land and full of gross growth. The reason of this is that they keep running to wood and make timber instead of flower buds; but once check that gross tendency it is easy to restrain after, for Nature then rights herself, and one crop leads on to another. It must be borne in mind, however, that root-pruning must not be carried out in a rough-and-ready fashion, as otherwise harm instead of good will result, for if roots are hacked and mutilated and severed too near to the tree, a long time will elapse before the tree will recover.

American Farmer, June, 1876
“Root-pruning can be done at any season of the year; but it is easiest performed in spring. The earth is then saturated with moisture, and is easily dug. Trees of three or four inches diameter (apple or pear,) should have their roots cut off from fourteen to eighteen inches from the trunk, [too near the stem ] and two and two and a half to three feet deep, [deeper than necessary, the roots of trees of that size never spread two feet below the surface.] Smaller trees should have the roots cut shorter, and larger longer. As a rule, the radius of the circle should be about five inches for every inch of diameter of the tree. The trench should go deep enough to cut all lateral roots. Enough roots must be cut to check the tree that the annual growth shall not exceed ten inches; and whenever the tree replaces the roots cut, so as to make excessive growth, the operation must be repeated."
     In case of pear blight, root-pruning must be done when the disease first appears. It will not do to delay, and, if well performed, seldom fails to effect a cure. A good sharp spade should be used.
     A correspondent of the American Agriculturist says: "To obtain fruit from barren trees, take coarse, strong twine, and wind it several times about the lower limbs of a tree and tie it as tight as possible. The next spring all the top above the cord will be as white as a sheet, and there will not be one blossom below. A neighbor seeing his trees loaded with pears, used the same method with the same success.”

Beaton (1851)
My next failure was with a beautiful climber, called Tecoma jasminoides, better known as a Bignonia. I have in vain striven to get this beautiful plant to flower very freely in-doors; but out against a wall, which is protected from the frost, it is a most beautiful thing, flowering as freely as can be from June to October, and it catches everybody's eye who comes near it. The mode of treatment is the same as that prescribed by Mr. Errington for a vigorous pear-tree. Main shoots are allowed to extend wherever there is room for them, and the side branches from these are stopped at a few joints, to form clusters of spurs, and on the young wood from these spurs the flowers come in long succession. Whenever the current growth refuses to give flowers, it is a sure sign the plant is getting too strong, and a few roots are cut to bring about a balance between them and the branches.

American Agriculturist, 3:29 (1844)
Pear-Training superseding the necessity of Root-Pruning.—Going over the pear quarter at the royal gardens at Versailles, I found from the head-gardener that he considered the tying-down the branches a sufficient check to overgrowth, without the assistance of root-pruning, except as regards any very free-growing varieties. Nothing could, to my mind, exceed the neatness and good-bearing of the pear-trees; they were of a conical shape and all the branches tied down so as to present the appearance of a conical chandelier, and of course much more bearing-wood obtained than in the trees which were stunted by root-pruning.


Art of Natural Bonsai by David Joyce (2006)
Craetaegus oxycantha (May Hawthorn)
Do not let dry out or let get root bound even though root bound trees flower better.
Azalea (satsuki) and Azalea (kurume)
Root-bound trees flower too much, and some flowers must be removed to avoid weakening tree.

The Garden Under Glass (1917) by William F. Rowles
Schizanthus.— A good open soil and firm potting will suit schizanthuses with no attempt at shading. Never should they want for water, while to allow them to remain root-bound is a deadly sin, the punishment for which is premature flowering and puny plants. It was at one time delivered to me as a doctrine that these plants would not bear feeding. This I have proved to be a heresy, for besides adding chemical stimulants liberally to the soil I have fed them with liquid cow manure and frequently top-dressed them with Peruvian guano.

Gardeners' Chronicle, June 13, 1908
Cymbidiums—plants in a root-bound state are always more productive of flower-spikes.

Journal of Horticulture and Home Farmer, 56: 116 (January 30, 1906)
Acalypha Sanderiana.— Well, I think a few remarks on stove flowering plants will not be out of place at this season. Beginning with Acalypha Sanderiana, this is a plant often neglected in the stove. I have heard the remark that it is not worth growing, simply because, through neglect, it has become root-bound in a small pot; then some day, when the stove is being overhauled, it is "shoved" into a pot several sizes too large for it. The result is that it grows to nothing but leaves and soft top growth, with an apology for a catkin here and there. If stuck under a glass in small pots in April, or even earlier, and given a shift as it requires, until it is put in a 7 in pot. (which is quite large enough to grow a specimen tree 3 ft or 4 ft high), a beautiful plant will result, with long catkins from the top to the rim of the pot. It should be grown as near the glass as possible, and given plenty of feeding when root-bound in its final pot.

Collins: Avocado (1905)
Some of the most prolific trees are those grown in rather small depressions of porous rock in southern Florida, where the plants are, in a manner, root-bound, while the porous nature of the rock affords good drainage.

The Garden, 63: 377 (May 30, 1903)
Cockscombs.— Balsams, Celosias, and other plants must be potted into their flowering pots before they become root-bound or they suffer a check. Cockscombs, on the other hand, are apt to grow away and refuse to produce their combs unless a check is given during the early period of growth. As soon as the combs are developed the plants require liberal treatment in every way and a gentle bottom heat.—J. Jaques. Wendover.

American Gardening, 24:701 (December 19, 1902)
Making the Most of the Cold Frame and Hot Bed
I. Forcing Cauliflower
Early vegetables are always appreciated and cannot be had too early to suit people who are expecting forced vegetables, and there is none that gives greater satisfaction, on the whole, than early Cauliflower. It is also a pleasure to the grower to cultivate subjects that give results so uniformly good as may be obtained from any of the many stocks of forcing Cauliflower obtainable to-day.
     Last year we used a selected strain of Snowball for the purpose, though any of the dwarf Erfurt varieties are suitable.
     It is high time to commence operations by the sowing of a pan of seeds in the greenhouse. Our first sowing is already up, and when these are transplanted, another sowing will be made and successions made until about six sowings have been put in. The demand, of course, will have to govern the quantity grown, but we find it impossible to have too many heads.
     The first transplanting of the plants is done into 2 1/2-inch pots, placing the seedling at the side of the pot, instead of in the centre. This will be found a great preventive against "damping off," as it is termed—it may also be called water-pot fever. Potting off young seedlings of any description may be much more rapidly done in this way, and the percentage of loss considerably reduced by this simple means. It is a well-known fact, too, that when a plant begins to feel the sides of the pot it rapidly progresses.
     When the plants are ready for a shift, they are transferred into 4-inch pots, using at this time a good, rich, light soil. A temperature of 50 to 55 degrees at night is most suitable. Given these conditions, it will not be long before a 6-inch pot will be needed.
     If it is intended to finish the crop in pots, the final shift may be to a 7-inch at this last potting.
     We prefer to finish the crop in a hotbed made up about March 15, planting out. By that time the plants will have become somewhat root-bound, which is a desirable condition, since it checks the tendency to leaf production and hastens the formation of the flower head. This state is an important one to be observed, for if planted out before this the depth of the average hotbed will not suffice as head room, and the foliage will become crippled and often frozen by getting in contact with the glass. The use of mats is avoided, reliance being put upon the latent heat from the soil to keep up the required temperature. Warmth at the roots and a cool top will perfect finer heads than where the plants are coddled and become puny from lack of light and air.
     The above details apply to all the earliest batches. The later sowings are planted in cold frames, without the aid of fermenting materials. These last lots are planted in frames that enjoy shade from the heat of midday. Cauliflowers delight in cool treatment and in late spring require protection from sun, or the foliage suffers, and consequently the heads are of poor color and quality.
     If any crop appears to come on slowly and a break in the supply is thereby threatened, use nitrate of soda in the water given, and the result will be magical. It is not desirable to use the nitrate in a general way, as it has a tendency to make the heads too large. Small ones are always preferred by the epicurean. —E. O. O.

The Garden [London] 54:42 (July 16, 1898)
Zonal Pelargoniums do not require any particular mixture of soils. In fact, poor soil to my thinking is better than rich combinations. The latter tend to the growth of leaves at the expense of flowers. My compost for these at all seasons is that which has done duty for other plants—Chrysanthemums and the like—and another most important item is to use comparatively small pots. When root-bound they flower most profusely.—H. C.

The Garden [London] 54:390 (Dec 12, 1898)
Zonal Pelargonium Guillon Mangilli.— I doubt if there is a better all-round zonal than this old variety. It is a very reliable winter bloomer, and there is no trouble to cut good trusses from it from November onwards. For summer flowering it is excellent, producing large heads of bloom in great profusion all through the season if the plants when root-bound are occasionally fed with weak liquid manure. I have plants of it now in 8-inch pots carrying about two dozen trusses, and these have given me a lot of bloom for cutting from the middle of June, and will continue to do so up to the close of the autumn. For the flower garden it answers better than the majority of double kinds, not making such gross growth as many of them, the flowers resisting heavy rains fairly well. Cutting struck in April and grown along freely will make good plants in 6-inch pots for winter blooming, and one-year-old plants cut back early in May, shaken out a little when they break, and replaced in pots one size larger, will furnish a quantity of bloom during the dull months of the year.— J. C. B.

The Garden [London] 54:390 (Dec 12, 1898)
GERANIUMS FOR WINTER AND SPRING BLOOMING. With the many and beautiful varieties of zonal Geraniums now in commerce, a house having a comfortable temperature can now be made very gay during the dull months of winter by specially preparing the plants for the purpose. For producing plants for winter blooming, the best way is to take stout cuttings in February. When rooted, grow them on as hardy as possible, shifting into 4 1/2-inch pots before they become pot-bound, keeping them close to the glass and giving abundance of air. At the beginning of June stand them in a sheltered position in the open air on a bed of ashes, pinching the growths when of sufficient length, and assisting the roots with liquid manure as soon as the 6-inch pots, which will be large enough for the plants to flower in, are becoming pretty well filled with roots. A good fibrous loam and some coarse sand suit them well. Keep all summer trusses of bloom picked off, and remove into a temperature of 50° early in October. Their somewhat root bound condition will induce flowering better than larger pots at this season. Even during the winter a gentle current of fresh air must be given in open weather to prevent the plants becoming drawn. For the production of large quantities of bloom during April, May, and June, plant out spring-struck cuttings along the edge of a Peach house or vinery border, allowing a distance of 2 1/2 feet between each and planting in a compost of good holding loam and a little leaf-mould and coarse sand. This mixture not only produces a short-jointed firm growth, but also allows of the plants being lifted in autumn with a good ball attached. Pinch the growths as soon as sufficiently advanced and train the plants by means of stout wooden hooks or pegs. Continue this practice till the end of August, never allowing the plants to suffer from want of water. About the middle of September well water the plants, and a few days later carefully lift each with as much soil as possible and pot firmly into 10-inch pots, placing in a frame and keeping rather close for a fortnight. When established in their new quarters, give plenty of air, and in October remove to a cool, airy position in the greenhouse, or even a cool vinery or Peach house. When growing freely in spring, assist twice a week with diluted liquid manure. Plants so treated will produce a plentiful and continuous supply of good trusses of bloom. It is best to throw away the old plants and raise a fresh lot every year. J. C.

Window Gardening,153-154 (1898)
Henry T Williams
Vallota Purpurea, is one of the finest Amaryllis, and is the most easily managed. They are not at all particular as to soil, will grow in any, but prefer the same as recommended for other Amaryllis But few plants answer as well or make as fine display for the window. Unlike most other plants, they do not require shifting but will grow from year to year in the same pot, tub or box without a change of soil, or other care than to give them plenty of water while flowering or in their growing state, and moderate watering the balance of the season. The foliage being persistent they require attention the whole year, but they can be kept under benches, in a light cellar or in any light room away from the frost during the winter, and in summer anywhere out of doors upon the piazza, the lawn, or if in pots, plunge in the border. They require but little pot room, in fact do better when root bound. The writer had a clump in a small tub last season that gave forty-one spikes of bloom; the plant was but five years from a single bulb. It is truly one of the finest, cheapest and most desirable cape bulbs.
     Its season of flowering is August and September, and we have neither been able to coax or drive it into flower at any other season.

Journal of Horticulture and Cottage Gardener 23:119 (August 6, 1897)
Tree Carnations.—All the earliest rooted Carnations are growing rapidly and fast filling their pots with roots. They must have weak stimulants every time they need water, clear soot water, or that made from cow manure being good for them; or, better still, artificial manure applied to the surface of the soil at intervals of two or three weeks. If neglected in this respect growth comes to a standstill, and flower spikes appear before they are wanted. Plants that are allowed to become root-bound early in the season are almost certain to come into flower in early autumn long before they are wanted. We have found it a good plan to place into larger pots any that are likely to become root-bound too early.

Garden and Forest, 7: 247 (June 20, 1894)
Cypripedium insigne.— We formerly had trouble in getting Cypripedium insigne to flower well, because we made the mistake of having very thrifty plants. They were treated to manure-water, and were green and vigorous, but when the time for flowering came the plants simply continued to grow and look strong, and did not flower. We now keep them in the coolest place in summer to prevent any second growth that might be induced by heat, and have left off giving manure-water except to such as are root-bound and really need it.
     We are trying Cattleyas and Laelias in a large, cool and airy structure for the summer, and they have improved in looks already. Small houses have a tendency to become overheated in the hot months of the year, far beyond the requirements of these plants. This causes the growths to mature early, and a second growth ensues. The plants are thus deprived of the absolute rest so beneficial in winter and conducive to satisfactory flowering.

Garden and Forest, 6:506 (1893)
Carnations may be grown outdoors to advantage during the summer, and when lifted and potted in the fall can be stored for a time in the pit or frame. In this way a regular supply of these useful flowers can be assured. Bouvardias should be treated in the same way for the summer, but after being lifted they require a higher temperature, and, therefore, had better not be placed in the frame. If kept warm and treated to a little stimulating food occasionally, the plants will soon become root-bound, when they will flower freely all winter long.

American Agriculturist, 52: 234 (April 1893)
Hibiscus not Flowering.—S. M. Wright. Clay Co., Ky.: The cause of failure of your Hibiscus sinensis to flower, after having been taken up from the garden, is a natural one. No shrub will thrive for a season after having been disturbed while in an active growing state. In disturbing its roots you have forced it into a premature rest, and its flowering buds were not developed. New buds will, in due time, form, and the plant will commence another season's growth. If the plants are expected to flower in winter, it will be much better not to take them out of the pot, but plunge them, so that the rim of the pots will be about an inch below the surface. Hibiscus have to be kept pretty well root-bound to flower freely.

The Culture of Vegetables and Flowers from Seeds and Roots (1892)
Sutton and Sons
Cockscombs.— The ideal Cockscomb is a dwarf, well-furnished plant, with large, symmetrical, and intensely coloured combs. Seeds of a first-class strain will produce a fair proportion of such plants in the hands of a man who understands their treatment. Sow in seed-pans filled with rich, sweet, friable loam, and place in a brisk temperature. Transfer the seedlings very early to small pots, and shift on until the size is reached in which they are to flower. Directly they become root-bound the comb will be formed, and having been grown entirely in heat, it is not improbable that the plants may be much too tall. If so, fill pots with suitable soil, using a size smaller than those already occupied; cut off the heads with a sufficient length of stem, remove a few of the lower leaves, and insert the stems firmly in the new pots. Place them on a hot-bed kept close and shaded for a few days, and if the specimens have been judiciously chosen and skilfully treated, there will be grand combs on dwarf plants.

American Florist, 2: 368 (May 1, 1887)
Calceolarias.— During the whole period of a calceolarias' life it requires copious waterings, and should never be allowed to become dry. Water gently, but abundantly, and under the leaves and not over head except in the case of young plants in the frames. In warm, summer weather I usually sprinkled the little plants overhead early in the afternoon, so that they might be well dried before night. I never give manure water till after they get root-bound in their flowering pots, and then stop it when the plants come into bloom. Always keep them covered up dry in the event of muggy, misty, or wet weather.—Wm. Falconer

Vick's Magazine, 9: 336 (1886)
Primula sinensis.— There is a very general custom of removing all flowers as a means of retarding the flowering period; but this is a mistaken impression, and instead of retarding or checking the flowers it is certainly shortening the season by the succession of bloom spikes coming much sooner than they would otherwise have done where the first flowers were allowed to develop. The only means of checking the early flowering of Primulas is to repot them as advised directly the pots are filled with roots. They will then continue growing instead of sending up flowers. This is the secret of having late Primulas in first-rate condition, for if once they are allowed to become root-bound up come their flowers. A small quantity of soot added to the soil is very beneficial.— A. Waters, in Journal of Horticulture.

The Floral World 4(7): 223 (July, 1869)
Hoya Bella Culture.—W. G., Salop.—This is by no means an expensive subject. You can get a thrifty little plant anywhere for half-a-crown. If you procure a plant at once, shift it into a pot one size larger, and place in an average temperature of 70°. Previous to potting, give the foliage a thorough sponging with warm water and a little soft soap, if in any way infested with scale or mealy bug, and then syringe with clear water, A thoroughly-drained pot and a light porous soil are indispensable requisites to the successful culture of this beautiful little Hoya. The compost should consist of two parts fibry peat, one part leaf-mould, and a good sprinkling of sand, small crocks, and nodules of charcoal. Stop the leading shoots to promote a bushy growth, and towards the end of August lessen the water supply, and place near the glass to thoroughly ripen the wood. This must be done in a careful and judicious manner, so that no sudden check is experienced. In the winter a temperature of 55° will be sufficiently high, and just enough water must be given to keep the foliage fresh. Shift early in February, and place in a growing temperature, as already advised. After a flowering size is attained, keep the roots rather pot-bound, as the plants then flower with greater freedom.

Choice Stove and Greenhouse Flowering Plants, 157-158 (1869)
Benjamin Samuel Williams
T. Schomburgkianus.—This fine Acanthaceous plant, which is perhaps better known under the name of T. rutilans, forms one of the most attractive and graceful plants for winter blooming with which we are acquainted. The leaves are oblong-lanceolate, tapering to a sharp point, and dark green in colour. The flowers are tubular, bright scarlet, borne in long pendulous racemes, which give the plant its peculiar graceful and elegant appearance. It is an abundant bloomer, producing its vivid flowers through the whole winter and spring months, and is a most glorious object for table decoration. The soil we find best adapted for it is a good light loam, with the addition of some well-decomposed manure and leaf mould, and a portion of silver sand. The plants should be kept growing as fast as possible until they attain a considerable size, and then kept root-bound, which will induce them to blossom more freely. After this, if the drainage is kept in good order, a little fresh soil is all that is necessary for a year or two, and then a batch of young plants should be ready to succeed the older ones. It requires a liberal supply of water and heat. Native of New Grenada.

Floricultural Cabinet, July, 1854: 180
Amarylis Belladonna in Pots.—I recommend any of your readers who wish to cultivate this plant in pots, to try the following experiment:—keep the plants constantly on a light shelf in the greenhouse, with a pan of wet sand unerneath them, which should never be allowed to become quite dry, not even in summer, when the plant is dormant. By this treatment some bulbs received from the Cape of Good Hope, which if not A. belladonna, can hardly be distinguished from that species, have flowered regularly every autumn in great luxuriance. They should never be fresh potted unless the roots split the pots, which some of mine have done, and of course the foregoing treatment must not be adopted till the bulbs have rooted themselves. This management was adopted accidentally as regards these bulbs, having been ordered, under the suggestion of the Rev. W. Herbert, for Brunsvigia Josephinae and multiflora, which were received at the game time, and which now flower regularly every other year. For some fifteen years before, I never succeeded in getting any of them to flower. The ordinary cause of failure in the cultivation of B. Josephinae is too much heat in winter, and want of moisture in summer,—J. R.

Apparent competition between vegetative phase and fruiting phase

Girdling, Ringing, Binding