s /^-o 1 lion Bulletin 465 November 1959 Propagation of Woody Plants By STUART DUNN and RUSSELL EGGERT Agricultural Experiment Station University of New Hampshire Durham, New Hampshire s ^-o 1 lion Bulletin 465 November 1959 Propagation of Woody Plants By STUART DUNN and RUSSELL EGGERT Agricultural Experiment Station University of New Hampshire Durham, New Hampshire Acknowledgement The authors wish to acknowledge the help of the following graduate research assistants in the conduct of the investigations reported in this bulletin: John R. Baker, DeWolf Merriam, George Williams, and Beyoung H. Kwack. Propagation of Woody Plants By Stuart Dunn and Russell Eggert 'T'HIS report is on a continuation of the work with sugar maple cuttings u f""""^^"^^^'^ previously (2), and on results with cuttings of apple and hazel-filbert hybrids. Many of the same techniques of gathering and handling the cuttmgs were again used. Since high moisture of the air around the cuttings by constant mist was shown to be important, this was further emphasized with some variations. Use of sawdust as a rooting medium had shown some promise, so further comparison of it with other materials was made. Since no survival of the rooted cuttings had been obtained after exposure to their first winter, considerable attention was given to this phase of the investigation. A description of variations from the methods previously developed will be given in the discussion of the results with different treatments. For some of the treatments, the results over a 5-year period, 1954-59 inclusive, are summarized. For others, shorter periods are involved. Effect of Kind of Propagating Bed There were in all 6 different kinds of propagating beds tested. (A) Greenhouse Ground Bed with Whiteivash Shade. This was a large bed 16' by 4' by 2' deep. Shade was provided by a fairly thick coating of whitewash on the greenhouse roof. For tests in two of the seasons, half of this bed was filled with sand, the other half with sawdust. For the rest of the time it was filled entirely with sawdust, except in the last year (1958) vvhen a part of it was filled with perlite. The maple cuttings used to fill this and all other beds were gathered and placed in the beds early in July as described before (2j. Their foliage was kept moist by constant mist, using oil-burner type nozzles (No. 4.00-60PLP ) delivering 4 gallons of water per hour. These gave a very fine mist which was ideal. See Figure 1 for type of bed and distribution of mist. Good drainage of the bed was provided by two lines of tile running its complete length. (B) Outdoor Bench ivith Cloth Shade, This was made with boards on bottom and sides, supported above the ground at waist level by 2" x 4" legs. It was made in three sections, each 6' x 3' and about 8" deep. A wooden frame supported a brown nylon netting for shade during two seasons. Later, woven Saran shading cloth was used and this was'^more satisfactory. This bench was supplied with the same rooting media and type of mist as the greenhouse bed. (C) Small Outdoor Bed tvith Cloth Shade. This was built of wood sides, directly on the ground. 6' x 3'. with a layer of coarse gravel beneath, and with a canopy of burlap for shade. This provided a low-cost propagating bed. It also had constant mist. Figure 1. Maple cuttings in ground bed with constant mist. This photograph shows the type of mist produced. (D) Plastic Covered Bench in Greenhouse ivith Fan Aeration. This was based on a report by Sweet and Carlson (4) in which they found that apple and cherry cuttings could be rooted in a bed supplied with inter- mittent mist in an air chamber covered with a canopy of plastic sheeting. Through this a stream of air was drawn by an exhaust fan. A bed very similar to this was set up, size 6' x 3', and filled with sawdust. It was supplied with intermittent mist, operated by the drying action of an "arti- ficial leaf" attached to a solenoid valve. (E) Greenhouse Bench Aerated from Beloiv. This was a wooden bench, 3' X 6', fitted with an air-tight metal bottom. Above this was a one-inch air gap. Above the air gap the medium rested on hardware cloth sup- jjorted by wood slats spaced one inch apart. This permitted air to pass continuously through the sawdust in which the cuttings were inserted. This bed also received interinittent mist. (F) Greenhouse Bench ivitli Tii^hl Plastic Cover. Several descriptions of this type of bed have been published in nursery trade journals and else- where. Typical of these is the one described by Coggeshall I f I . Essential- ly, this consists of a propagating bed enclosed above by a moisture-tight covering of plastic sheeting supported usually by wire netting at some distance above the cuttings. Theoretically this is supposed to need little or no additional water, the vapor from the water-soaked medium keeping the air al)ove the cuttings saturated. A bed similar to this was set up at one end of a greenhouse bench, and, to aid in cooling the interior, several thicknesses of cheesecloth on top of the plastic cover were sprinkled with water at intervals. Water was added to the cuttings and medium fairly often. The temperature rose to a very high point (95-105°F.) in this "sweat- box" type of bed on warm summer days. This was tested for only one season. Table 1. Effect of Kind of Bed and Moisture Treatment on Rooting of Sugar Maple Cuttings Total Nc . of Moisture No. of Number N umber Percent Seasons Supply Kind of Bed Cuttings Rooted Callused Rooted Te^ ited Greenhouse ground bed — whitewash shade 3660 1068 1112 29 5 Constant Outdoor bench — mist cloth shade Small outdoor ground 2988 814 920 27 4 bed • — cloth shade 450 166 23 37 2 Intermittent Plastic covered bench mist — greenhouse — fan aerated 570 163 160 28 2 Greenhouse bench aerated from below 225 23 79 10 1 Moisture Greenhouse bench with sealed in — tight plastic cover 318 74 145 23 ? watered as needed The results of tests in all beds are summarized in Table 1. Based on the percentage of rooting, the small outdoor ground bed with cloth shade (C), gave the best response (37 percent). Although the total number of cuttings tested in it was relatively small, this type of bed does have definite possi- bilities. The chief recommendations for it are simjilicity of construction and ease of operation, plus low cost. Bed (A), greenhouse ground bed with whitewash shade and constant mist, proved to be next best in rootino- re- sponse (29 percent), although the margin was slight between the resuUs with it and those with type (B). outdoor bench with cloth shade and con- stant mist (27 percent), and those with bed (D), the plastic covered bench with fan aeration and intermittent mist (28 percent). However, the extra expense, care, and trouble encountered with intermittent m.ist devices, whether with or without special covers or aerating fans, would be dis- tinctly against the use of this method. As to type (F), the bench with moisture-tight cover, the somewhat lower rooting response (23 percent), together with the extra care and attention it requires, do not recommend this type of bed. Lowest amount of rooting of all beds was obtained with bed (E), the one with forced aeration from below, (10 percent). On the basis of these results this method is not worth further consideration. From all the results the general conclusion may be drawn that the use of beds or benches either in the greenhouse or outdoors, with constant mist and some shade, will provide good rooting conditions for sugar maple cuttings. Effects of Medium on Rooting As mentioned in the publication cited above (2). earlier results had shown sawdust to have promise as a rooting medium in contrast to sand. Prior to this published report, preliminary experiments had shown mixtures of sand and peat in various proportions, and waste bark to be inferior to sand alone. In order to definitely establish the value of sawdust in this re- spect, for two seasons a comparison of sawdust was made with sand. Separ- ate portions of two different beds were filled with each material. Both media were tested with nearly equal numbers of cuttings from each clonal source. Those cuttings were given similar treatment. In another season a similar comparison was made of perlite with sawdust. The results of these tests are summarized in Table 2. These show that sawdust is superior to either of these other two materials as a rooting medium under the conditions of these experiments. It may be mentioned that sawdust has other advantages. One is that it is much lighter in weight than sand, and therefore easier to handle and store. It is usually cheaper than other media and easily obtainable. Table 2. Effect of Medium on Rooting of Sugar Maple Cuttings Number Number N umber Percent Year Medium Tested Rooted Callused Rooted Sand 664 143 255 21 1954 Sawdust 648 182 238 28 Sand 838 115 114 12 1955 Sawdust 838 200 194 25 Sand 1502 258 369 17 Totals Sawdust 1486 382 432 26 Sawdust 168 54 44 32 1958 Perlite 168 19 35 11 Effect of Growth Regulators The data reported previously (2) had shown some slight advantage for growth regulator treatments, the best one being indolbutyric acid at 0.1 percent strength (quick-dip method). For further information, tests were continued with a few of these substances for two more seasons. Also, on recommendation by Dr. P. W. Zimmerman of the Boyce Thompson Insti- tute (personal comitiunication ) , the dry powder manufactured by Merck and Co., knowir as Hormodin No. 3. was tested for two additional seasons. The results are summarized in Table 3. Here again, some slight superiority is shown for one of the growth regulator treatments over the controls, but probably not enough to warrant the extra labor and expense of treatment with these materials. Table 3. Effect of Growth Regulators on Rooting of Sugar Maple Cuttings Part A. Solution Treatments — Quick-dip Method Treatment Number Tested Number Rooted Ni Ci .imber illufed Percent Rooted Control 1002 274 232 27 Indolbutyric acid 0.1 % 0.02% 0.01 7o 348 562 308 122 113 82 91 80 133 35 24 26 Indolacetic acid p-chlorophen- oxyacetic acid 0.1 % 0.01% 0..5 % 323 292 562 86 68 74 92 102 71 26 23 14 Naphthalene- acetic acid 0.02% 261 49 42 20 For growth regulators, totals and average % rooting exclusive of that for p-chlorophenoxyacetic acid 2094 520 Part B. Drv Powder Treatment Control Hormodin No. 3 828 828 247 289 540 380 183 25 30 35 Clonal Differences Some variations in rooting of sugar maple cuttings from different clones were observed previouslv ( 2 ) . For each season of the work reported here, records were kept of the rooting response of the cuttings from different trees. The records are summarized in Table 4. Trees numbered 3, 4, 5. and 6 were part of a row of old trees along a roadway at the Horticultural Farm, University of New Hampshire. Records kept of trees 3 and .5 have shown their sap to be exceptionally high in sugar content. Tree 3 is ex- ceptionally vigorous with a pronounced "bushy" type of top growth. In Table 4. A Summary- of Clonal Differences in Rooting of Sugar Maple Cuttings over a 5-year Period, 1954-1958 Number of Number Number Number Percent Tree No. Seasons Tested Rooted Callused Rooted 3 5 2074 906 416 43 4 4 1345 329 411 24 5 5 2208 194 1093 9 6 4 645 217 93 33 8 4 1198 433 302 36 9 4 635 235 97 37 Totals 8105 2314 2412 28 (Ave.) contrast, tree 5 is less vigorous and has fewer scaffold limbs. Whether this type of growth has anything to do with the high percentage of rooting by cuttings from tree 3 is unknown. Tree 8 is actually a closely-growing clump of three main trunks, medium in age (about 20 years) and very vigorous. This clump grows near a loading dock. Tree 9 in Table 4 represents cuttings taken from several young trees I perhaps 10 to 15 years old ) at the edge of the clearing at this general location. It is evident that the clonal source of cuttings does make a great difference in rooting response. Of especial interest is the contrast between rooting of those from Tree 5 (9 percent) and Tree 3 (43 percent). Both are old trees and high in sugar yield, but differ in vigor and growth habit. It should be mentioned at this point that it is often difficult to collect a large uniform group of cuttings from any one tree or clonal source. Fre- quently the greenwood shoots are too short to make good cuttings. On the other hand, cuttings from water-sprouts that are too long and have grown too rapidly are prone to rot very readily. This must be taken into account in making comparisons of effects of various factors, such as growth regu- lators, media, etc., within a group of clonal material. In connection with the matter of clonal differences, it may be mentioned that Muckadell ( 3 ) has presented some evidence that younger portions of a woody plant are more active in many ways. It seemed desirable to de- termine if cuttings taken from the topmost part of an old maple tree would root better than those taken lower down. A small number of cuttings were taken in 1957 from near the top of Tree 3 (a very tall tree), and records kept of their rooting as compared to those taken in the usual way in an area extending from the base of the foliage up to a height of about 16 or 20 feet. From a total of 111 cuttings taken from the top there were 43 rooted or a percentage of 39. Of the total number of 485 cuttings taken lower on the tree. 279 or 57 percent rooted. On the basis of these rela- tively few cuttings there is no advantage shown for taking them from the top part of the tree. However, it is probably unsafe to regard this as very conclusive evidence, since the sample was not large, and was taken for only one season. The Survival of Rootecl Cuttings From the evidence presented here, and in the published report (2), the problem of rooting fairly large numbers of sugar maple cuttings can be regarded as being virtually solved. However, the additional problem of se- curing their survival through one or more winters following their root- ing is only partially resolved. It may be noted at this point that usually only the most vigorously rooted cuttings were chosen for potting and keeping for survival tests. This was true except in instances of clones where rooting was poor and scanty, as in the cuttings of Tree 5. Examples of vigorous rooting and weak rooting may be seen in Figure 2. Single, "club-shaped" roots of the type on the bottom side of the photograph were very weak and easily broken. Rooted cuttings of this type were usually discarded. Previous to the year 1955 all of the rooted maple cuttings had been potted in early fall and later when fall rains started were set out in a specially prepared nursery bed at the Horticultural Fann. These were mulched rather deeply with sawdust after the ground was partly frozen, and were Figure 2. Types of rooting in sugar maple cuttings. Those at the top are vigorous; those at the bottom, Meak. further protected by a wooden inverted V-shaped sheUer of lath. None of the cuttings thus treated survived the winter. At the close of the rooting season of 1955 half of the rooted cuttinas were o;iven this same treatment and the other half were potted and were packed in boxes with sawdust up to the tops of the pots. They were taken to the Horticultural Farm and left on the ground beside the barn to harden. At the onset of very cold weather, just before the final freeze-up, they were placed in a sheltered room beneath the barn, where they were covered with a thick layer of sawdust on all sides and top, held in place by heavy building paper. The following May the boxes of rooted plants were moved into daylight outside the barn and evidence of survival awaited by renewal of vegetative growth. Of 200 plants thus treated. Ill or 57 percent were alive on May 20, 1956. By Septend:)er 1. 1956. about 45 were alive and growing in the field. Of those planted directh in the nursery the previous fall, none sur- vived. Based on this kind of evidence, for all subsequent seasons the rooted cuttings were given the same kind of sawdust packed treatment that had resulted in some survival. The same technique did not result in equal success in securing survival in later seasons, however. Also there has been further mortality in those plants surviving the first winter in the field. Of those kept over winter from the seasons of 1957 and 1958. none have survived to date. The reasons for this are somewhat obscure, but it seems evident that the temperature dropped too low in the storage area at some time during these two winters. At Table 5. Survival of Cuttings — Sugar Maple in Nursery Row as of June 5, 1959 From 1954 Rooting From 1955 Rooting From 1956 Rooting Tree No. and 1955 Planting and 1956 Planting and 1957 Planting No. 3 1 No. 4 4 No. 5 0 Y.T. (No. 9) 11 L.D. (No. 8) 14 Totals 30 3 Total of all surviving 36 present the survival score stands as given in Table 5. These are all vigor- ous and growmg well. This is not a very impressive total from the thous- ands of cuttmgs that have been rooted, but it shows that it can be done! At this point, a few comments and suggestions may be in order, to serve as a guide to those who may wish to propagate woody plants by these methods or to improve upon them. One chief problem is the pot-bound condition of the potted cuttings at the time of placing them in the nursery row. it takes a long time for side roots to become established and such plants are not anchored as well as they should be. Another is that they seem to require a winter temperature slightly above 32 °F., but which does not fall below that point. Perhaps the solution to both problems would be to transplant the rooted cuttings directlv to a cutting bed which will later be held in refrigeration at 32° to 34° F. until the end of the winter period. Experiments on Cuttings of Hazel-Filbert Hybrids and Young Apple Stock To explore the potential applications of the methods found effective in rooting maple to other woody species, tests were made on a limited number of cuttings from apple stock and from hybrids of hazel-filbert. These were taken from young trees at the Horticultural Farm. Experiments were made on the effects of growth regulators with both kinds of cuttings and on the effect of taking cuttings from different positions on the plant (lateral vs terminal) with Mains robusta No. 5 in 1955 and 1956. The cuttings were 10 all tested in the sawdust-filled bench (outdoors) with constant mist. The results of these experiments are summarized in Tables 6 and 7. It is shown there that cuttings of M. robusta responded with a higher percentage of Table 6. Effect of Growth Regulator;* on Rooting of Cuttings of Malus robusta No. 5 Part A, Solution Treatments — Quiek-dip Method Treatment Number Tested Number Rooted Nunilier Callused Percent Rooted Control Indolbutyric acid 0.1 % 0.02% 0.01% 1.56 32 72 64 68 19 25 31 61 7 15 27 43 59 35 48 Indolacetic acid 0.1 % 0.01% 32 32 16 17 13 14 50 53 Part B. Dry Powder Treatment Control Hormodin No. 3 42 70 22 35 16 28 52 50 Table 7. Effect of Growth Regulators on Rooting of Cuttings of Hazel-Filbert Hybrids Treatment Number Tested Number Rooted Number Callused Percent Rooted Control 106 13 42 12 Indolbutyric acid 0.1 7o 0.02% 0.01%, 16 54 32 - 3 11 5 4 17 15 19 20 15 Indolacetic acid 0.1 % 0.01% 16 32 2 3 9 11 12 9 p-chlorophenoxyacetic acid 0.5 % 54 0 3 0 Naphthalene acetic acid 0.02 7o 36 1 16 0.3 rooting than those of hazel-filbert. Some advantage is shown for growth regulator treatments, except for that in dry powder form (Hormodin No. 3). It is evident that these methods can be used successfully on other woody plants besides sugar maple. That there is a definite advantage in taking cuttings from the terminal position over those in the lateral position w^ith M. robusta No. 5 is shown in the summary for two years results in Table o. The limited tests on two clones of apple in 1958 I Table 9) indicate that rooting by M. robusta No. 5 was better than that of N. H. .55 stock. 11 Table 8. Effect of Position on Plant (from Mhich Cnttings were taken) on Rooting of Malus robusta No. 5 Year Position Number Tested Number Rooted Percent Rooted 1954 1955 Terminal Terminal Totals Lateral Lateral Totals 96 90 78 56 81 62 1954 1955 186 112 90 134 31 11 72 (Ave.) 27 12 202 42 20 (Ave.) Table 9. Clonal Differences in Rooting of Apple Cuttings, 1958 Number Number Number Percent Clone Tested Rooted Callused Rooted N. H. 55 42 13 29 31 Malus robusta 5 70 44 15 63 Summary 1. Propagating beds or benches filled with sawdust and provided with constant mist and moderate shade were more satisfactory for rooting cuttings of woody plants than beds with other media or with special aerating devices or with intermittent mist, under the conditions of this experiment. 2. The use of growth regulators may produce somewhat higher per- centages of rooting in such cuttings, but it is doubtful if the advantage is worth the extra work and expense of their use. 3. Clonal variations in rooting response are very pronounced. The factors that influence these variations are largely unknown. 4. The problem of securing rooting of cuttings of the species of woody plants used in this experiment may be regarded as solved. It can be done with a fair degree of success, with methods described here. The problem of securing survival of the rooted cuttings of sugar maple during succeeding winters after their rooting, remains a very large one. The results presented here show that it can be done, with proper care. However, the percentage of survival is yet very small and it is toward the goal of increasing that percentage that future work should be directed. Literature Cited 1. Coggeshall, Roger. Asiatic maples, their propagation from softwood cuttings. Arnoldia 17:45-56. 1957. 2. Dunn. Stuart and Townsend, R. J. Propagation of sugar maple by vege- tative cuttings. Jour. For. 52:678-79. 1954. 3. Muckadell. M. Schaffalitskv de. Juvenile stages in woody plants. Physiol. Plantarum 7:782-96, 1954. 4. Sweet. D. V. and Carlson, R. F. Rooting of cuttings in air-cooled mist chamber. Mich. Agr. Exp. Sta. Quart. Bui. 38:258-67, 1955.