Proc. Soc. Hort. Sci 3: 34-37 (1905)
FORCING RHUBARB IN THE DARK
W. R. LAZENBY,
Ohio State University, Columbus, Ohio.

During the past eight years the Horticultural Department of the Ohio State University, as a part of its illustrative work in the winter forcing of vegetables, has been growing rhubarb in the dark. Although several reports of the methods employed and results secured have been published, the numerous inquiries show that the subject is not generally understood.

The forcing of rhubarb is an old practice, but the method of growing it in complete darkness in ordinary house cellars, basement rooms, and other places where light is totally excluded, is comparatively new. This new method is not only simple but profitable, and is increasing the popularity of this old garden esculent.

The philosophy of the practice, and the scientific principles upon which it is based may be briefly stated as follows: In a large leaved perennial like the rhubarb, food is prepared much faster than it is consumed, and we find a special accumulation in the roots. Under suitable conditions this stored supply of reserve food may all be expended in one succeeding period of growth, and this growth be in the best possible form for the use of man.

This desired growth is associated with a remarkable alternation of vigorous activity and rest. Just why growth is resumed so energetically after the rest period is not easily explained. Some tests with rhubarb roots show that either artificial freezing or drying will take the place of the natural long rest period. This gives us a hint that natural exposure to cold in the case of cool and moist seasons or climates, and a similar exposure to drouth in warmer and drier ones, may account in part for the remarkable activity seen after the rest period.

The growth taking place in complete darkness, no chlorophyll is formed, and consequently that interesting process known as photosynthesis does not take place. The nutritive processes are those of transformation rather than those of creation.

The effect of the exclusion of light is seen in the form, color and texture of the leaf, and likewise in the water, acid and aromatic content.

Regarding the form the principal difference is seen in the moderate lengthening of the petiole or leaf stem, and a wonderful reduction of the lamina or leaf blade. Like the eye that only develops in the light or where it can be of use, so this part of the leaf, the special organ of photosynthesis is developed in a very rudimentary way.

The green color which depends upon light for its existence, is wholly absent, and the stems according to variety range from pure white to various shades of pink.

The texture is more crisp and delicate, due to the lessened development of the woody fiber. The skin is greatly reduced in thickness and is not readily separated from the stem, the bast tissue especially being poorly developed. The water content is increased from 6 to 10 per cent. This may seem objectionable, but when we reflect that the juices of the rhubarb like those of more delicate vegetables, and fruits generally, contain a considerable quantity of organic acids, together with more or less sugar, the increase in water may improve the flavor. In rhubarb grown in the light, the acid content is usually too high in proportion to the sugar, and the decrease lends quality and an improved flavor to the dark grown product. With the results of partial shading in mind, it might be thought that rhubarb grown in total darkness would be small, spindling and unpalatable, but such is not the case.

Until the root becomes exhausted, its size is satisfactory, color attractive, and quality unexcelled. It has a thin tender skin, is crisp and brittle, and has a sprightly flavor.

The methods we have employed in forcing rhubarb are as follows. The roots are plowed out in early winter before the ground freezes. Where only a few roots are required for home use they may be dug by the use of the spade, but the grower for commercial purposes will find the plow more economical of time and labor.

A furrow is run close to the row on one side throwing the soil away from the roots. Then run a furrow the same way on the opposite side. The roots are then lifted out and all the smaller rootlets cut off with a spade or a shovel. Pains should be taken not to injure any of the larger roots, and it is well to allow a considerable amount of soil to adhere to them. The roots are left on the surface of the ground until they have been well frozen. This seems to be essential to a prompt, energetic growth. After freezing they may he removed at any time to the pit, cellar or basement, where they are to be grown. The roots should be set close together, and all spaces between should be filled with soil. Regular, well-trimmed roots can be crowded into a small space without injury, if care is taken to get them well surrounded with soil. All crowns should be covered to the depth of two or three inches. About every four feet a narrow passage way should be left for convenience in gathering the crop. After the roots are in place they should be thoroughly moistened, and all light excluded. The more intense the darkness the better.

The question of temperature is an important one. It may range from 55 to 70 F. If the temperature is high, the growth is more rapid and the cutting season sooner over. If low, the growth is much slower and the season longer. For home use a temperature ranging from 55 to 60 F. would be desirable. If the crop is grown on a commercial scale from 60 to 65 F. may be none too high.

At the higher temperature one can begin to market the crop in twenty days from the date of setting out the roots, and cuttings can be made for about four weeks. At the lower temperature it would require thirty days before the first cutting, and the roots would continue to produce for at least six weeks.

It is generally believed that roots from three to five years old are the only ones that can be profitably used for forcing. But this is a mistake. We have demonstrated that roots of one season's growth can be used with satisfaction and profit. Briefly stated, our experience has been as follows. Rhubarb seed preferably of the Linnaeus type is sown early in April, just about as soon as the soil is fit to work. The soil, a sandy loam, is well enriched with stable manure. The seed is sown with an ordinary garden drill, in rows twenty-four inches apart. The seed usually comes up well, and if the season is a fairly favorable one, the young plants grow rapidly. They are carefully cultivated until the leaves become so large as to interfere with the passage of the cultivator between the rows. By the middle of August many of the leaf blades measure twelve inches across, with stems from fifteen to twenty inches long and an inch in diameter.

We had not thought of using these seedling roots for forcing until two or three years ago, when having more crowns than we cared to transplant, it was decided to give them a trial. Accordingly, every other row was plowed out in December and one forcing cellar filled with the young roots.

Having roots enough to fill the cellar the second time, these were left on the ground, and covered with a thin layer of soil, to prevent injury from irregular drying or alternate freezing and thawing in a basement room.

The roots for the first crop were placed crown upward, in a basement room and packed closely together. The weight of the roots, including a little adherent soil, usually range from two to five pounds each. In three or four days after setting, the stalks begin to push through the soil, and in about three weeks thereafter we have some of the finest rhubarb imaginable. From these roots of a single season's growth we usually cut or pull the stalks from four to six times. The first two or three cuttings give the finest stalks, and then they gradually diminish in size, but are of good marketable quality. The period of marketing covers about four weeks so that a second crop can be grown in the same place before the outdoor plants are ready for use.

The exhausted roots are easily removed, and the same soil is used to cover the second crop.

The second crop develops about the same as the first, but as the weather is usually warmer care must be taken not to allow the cellars to become too warm.

In order to give a better idea of the size of the stalks the following weights and measurements are presented: Twelve stalks averaged as follows:

Average weight 4.64 oz.
Average length of petiole 17.33 in.
Average length of leaf blade 4.45 in.
Total length of leaf 21.79 in.
Average width of leaf blade 3.02 in.

In regard to the profits from the "new rhubarb culture" I have only this to add. In the very first test made by us, the product from a space 8 x 10 feet sold for over $10 or more than five times as much as we could have realized from a single crop of the same roots grown out of doors in the ordinary way. From a double crop grown in 185 square feet of space we sold $35.55 worth and this came from seedling roots.

In these tests no special effort was made to push the commercial side of the business, but the results were certainly satisfactory in a financial way. Near our large commercial centers, and under good management this new industry should pay splendidly. All that is needed is a careful preparation of soil, a wise selection of seed, proper thinning and good cultivation, and roots of one season's growth will yield a handsome profit. When not grown in a commercial way a succession of fine rhubarb during winter, when fresh vegetables are scarce and expensive is within the reach of all who have a garden plot and cellar.

See also: Hare 1816


CybeRose note: Aside from the practical interest, this article reminds us that growth (increase in mass) and development (differentiation) are separate processes. The rhubarb stalks grow in complete darkness, but their development is different from what occurs in light. Woody fibers do not develop so readily, and the juice is less acid. Of course, the same principle has long been employed to improve the quality of leeks, cauliflowers, asparagus and other vegetables that can be shaded in some way—by mounding soil around them or covering the heads with leaves.

In one of his "Stalking the wild ..." books, Euell Gibbons recommended the same procedure for raising curly dock in the dark for use in winter salads.

It is interesting to note that in 1905 the price of gold was $21 per ounce. Today (May 28, 2009) it stands around $960, or about 45.7 times as high. That means that the author's $10 crop could be valued nearer $457. Not bad for an 8 x 10 cellar. The larger, double crop of $35.55 is equivalent to about $1624.65.