Resources for Growing Hemp

Drug Plants Under Cultivation USDA_Bulletin - 1915

Hemp Cultivation

How Weather Effects CBD Content in Hemp Plants

Growing Hemp

Hemp - A new crop with new uses

From the 1913 USDA Yearbook of Agriculture


Hemp loosens the soil and makes it more mellow. The soil is shaded by hemp more than by any other crop. The foliage at the top of the growing plants makes a dense shade and, in addition, all of the leaves below the top fall off, forming a mulch on the ground, so that the surface of the soil remains moist and in better condition for the action of soil bacteria. The rather coarse taproots (pI. XLI, fig. 3), p.ene- trating deeply and bringing up plant food from the subsoil, decay quickly after the crop is harvested and tend to loosen the soil more than do the fibrous roots of wheat, oats, and similar broadcast crops. Land is more easily plowed after hemp than after com or small grain.'

Very few of the common weeds troublesome on the farm can survive the dense shade of a good crop of hemp. If the hemp makes a short, weak growth, owing to unsuitable soil, drought, or other causes, it will have little effect in checking the growth of weeds, but a good, dense crop, 6 feet or more in height, will leave the ground practically free from weeds at hfrvest time. In Wisconsin, Canada thistle has been com- p etely killed and quack-grass severely checked by one crop ~ hemp. In one 4-acre field in Vernon County, Wis., where Canada thistles were very thick, fully 95 per cent of the thistles were killed where the hemp attained a height of 5 f{'et or more, but on a dry, gravelly hillside in this same field where'it grew only 2 to 3 feet high, the thistles were checked no more than they would have been in a grain crop. Some vines, like the wild moming-glory and bindweed climb up the hemp stalks and secure light enough for growth, but low- growing weeds can not live in a hemp field.

An abundant supply of plant food is required by hemp, but most of it is merely borrowed during development and returned to the soil at the close of the season. Hemp requires for its best development a richer soil than any of the other crops mentioned except sugar beets. These other crops, except the stalks of com and the tops of beets, are entirely removed from the land, thus taking away nearly all the plant food consumed in their growth. Only the fiber of hemp is taken away from the farm and this is mostly cellulose, composed of water and carbonic acid. The relative proportions by weight of the different pa.rts of the hemp plant, thoroughly air dried, are approximateJy 88 follows: Roots 10 per cent, stems 60 per cent, and leaves 30 per cent.

The foliage, constituting nearly one-third of the weight of the entire plant and much richer in essential fertilizing elements than the stalks, all returns to the field where the hemp grows. The roots also remain and, together with the stubble, they constitute more than 10 per cent of the total weight and contain approximately the same proportions of fertilizing elements as the stalks. The leaves and roots therefore return to the soil nearly two-thirds of the fertilizing elements used in building up the plant.

After the hemp is harvested, it is spread out on the same land for retting. In this retting process nearly all of the soluble ingredients are washed out and returned to the soil. When broken in the field on small hand brakes, as is still the common practice in Kentucky, the hurds, or central woody portion of the stalk, together with most of the outer bark, are left in small piles and burned, returning the mineral ingredi- ents to the soil. Where machine brakes are used the hurds may serve an excellent purpose as an absorbent in stock yards and pig pens, to be returned to the fields in barnyard manure. The mineral ingredients permanently removed from the farm are thus reduced to the small proportions contained in the fiber.

Hemp is recommended to be grown in rotation with other farm crops on ordinary upland soils suited to its growth. In ordinary crop rotations it would take about the same place as oats. On some of the farms in California hemp is grown in rotation with beans. If retted on the same land, however, it would occupy the field during the entire growing season, so that it would be impossible to sow a field crop after hemp unless it were a. crop of rye. The growing of rye after hemp has been recommended in order to prevent washing and to retain the soluble fertilizing elements that might otherwise be leached out during the winter. This recommendation, however, has not been put in practice sufficiently to demonstrate that it is of any real value. Hemp will grow well in a fertile soil after any crop, and it leaves the land in good condition for any succeeding crop. Hemp requires a plentiful supply of fer tilizing elements, especially nitrogen, and it is therefore best to have it succeed clover, peas, or grass sod. If it follows wheat, oats, or com, these crops should be well fertilized .with barnyard manure.

Hemp leaves the ground mellow and free from weeds and is therefore reeotnmended to precede sugar beets, onions, celery, and similar crops which require hand weeding. If hemp is grown primarily to kill Canada thistle, quack-grass, or similar perennial weeds, it may be grown repeatedly on the same land until the weeds are subdued.

Hemp requires an abundant supply of plant food. Reaching in four months a height of 6 to 12 feet and producing a larger amount of dry vegetable matter than any other crop in temperate climates, it must be grown on a soil naturally fertile or enriched by a liberal application of fertilizer. In Europe and in Asia heavy applications of fertilizers are used to keep the soils up to the standard for hemp, but in the United States most of the hemp is grown on lands the fertility of which has not been exhausted by centuries of cultivation.


The best single fertilizer for hemp is undoubtedly barnyard manure. It supplies the three important plant foods, nitrogen, potash, and phosphoric acid, and it also adds to the store of humus, which appears to be more necessary for hemp than for most other farm crops. If other fertilizers are used, it is well to apply barnya.rd manure also, should be applied to the preceding crop, or, at the latest, in the fall before the hemp lS sown. It must be well rotted and thoroughly mlXed with tne soIl be- fore the hemp seed is sown, so as to promote a umform growth of the hemp stalks. Uniformity in the SIze ot the plants of other crops ~ of httle consequence, but m hemp it . is a matter ot pnme Importance. An application of coarse manure in the spnng, just before sowing, is likely to result in more injury than benefit. The amount that may be ap- plied profitably will vary with different soils. There is little danger, however, of mducing too rank a growth of hemp on upland soils, provided the plants are uniform, for it must be borne in mind that stalk and not fruit is desired. On soils deficient in humus as the result of long cultivation, the increased growth of hemp may well repay for the application of 15 to 20 tons of barnyard manure per acre. It would be unwise to sow hemp on such soils until they had been heavily fertilized with barnyard manure.


Beans grown before hemp and the vines plowed under have given good results in increased yield and im proved quality of fiber on alluvial soils at Courtlancl", Cal. Clover is sometimes plowed under in Kentucky to enrich the land for hemp. It must be plowed under during the preceding fall, so as to become thoroughly rotted before the hemp is grown.


In experiments with various crops for green manure for wheat in India, hemp was found to give the best results.! In exceptionally dry seasons, many fields of hemp do not grow hlgh enough to be utilized profitably for fiber production. They are often left until fully mature and then burned. Better results would doubtless be obtained if the hemp were plowed under as soon as it could be determined that it would not make a sufficient growth for fiber production. Mature hemp stalks or dry hurds should not be plowed under, because they rot very slowly.

PDF file of complete 72 page article published in 1913