UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA FORCING GLADIOLUS OUTDOORS BY HEATING THE SOIL WITH ELECTRICITY JAMES R.TAVERNETTI AND S. L. EMSWELLER BULLETIN 584 OCTOBER, 1934 UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA FORCING GLADIOLUS OUTDOORS BY HEATING THE SOIL WITH ELECTRICITY 1 2 JAMES E. TAVEENETTF and S. L. EMSWELLER 4 The growing of gladiolus outdoors for cut flowers is an important part of the floral industry in the United States. According to the Cen- sus of 1930, this crop then comprised slightly over 26 per cent of the land area used and over 29 per cent of the value of all cut flowers grown in the open. This popularity results from the wide adaptability of the gladiolus to different types of climatic and soil conditions and from its use both as a cut flower and as a decorative plant. The wide range of color and type, the ease of growing, and the long season of bloom are also contributing factors. Although the early cut flowers bring a higher price, little or no at- tempt has been made to produce them outdoors. The common practice is to plant the corms as soon as possible for the earliest crop and to make successive plantings every few weeks. The time required to produce the flowers varies with the climate. It is often unduly prolonged by low soil temperatures that cause early planted corms to lie dormant for a long period. Because of its convenient adaptability and relatively low initial cost, heating the soil by electricity has recently stimulated interest in the forcing of gladiolus outdoors. In order to determine the effect and costs of this method of forcing outdoors, a series of experiments was con- ducted at Davis during the winter and spring seasons of 1931, 1932, and 1933. The first year, plants were grown in an uncovered frame; the second, in the open field; and the third, in a covered frame. In all the experiments the corms used were between 1% and 2 inches in diameter. They were dug about October and were held in storage i Received for publication July 6, 1934. 2 This publication is the twelfth of a series reporting results of investigations conducted by the California Agricultural Experiment Station in cooperation with the California Committee on the Relation of Electricity to Agriculture. 3 Associate in Agricultural Engineering. * Assistant Professor of Truck Crops and Assistant Olericulturist in the Experi- ment Station. [3] 4 University of California — Experiment Station until planted in a basement where the temperature varied between 54° and 59° Fahrenheit. Each year all corms were dipped in Semesan as soon as they had dried out after harvest, and again a few days before planting. Only sound, healthy ones were used. Fig. 1. — A piece of the heating cable used for warming the soil. It consists of an insulated resistance wire enclosed in a lead sheath. A 60-foot length connected to a 110-volt circuit will heat about 4 square yards of soil. This cable costs about five cents per foot. The soil was warmed by a special heating cable (fig. 1), consisting of a resistance wire insulated with felted asbestos and enclosed in a lead sheath about ^4 inch in diameter. This cable had a resistance of % onm per foot and was connected to a 110-volt circuit. FORCING IN UNCOVERED FRAMES In 1931 the corms were grown in an uncovered frame 6 x 15 feet, half of which was heated and half unheated (fig. 2). A space of 1 foot was left between the two plots. The heat was furnished by 45 feet of soil- heating cable, which was looped back and forth, as shown in figure 2, and buried 5 inches deep in trenches 12 inches apart. The total con- nected load was about 500 watts for the bed or about 12 watts per square foot. Bul. 584] Forcing Gladiolus Outdoors with Electricity Fifty-four corms of the Prince of Wales and 36 of the Shay lor varie- ties were planted in each bed on December 15, 1930. There was 1 foot between the rows, which were midway between the legs of the cable loops; and the corms were spaced 4 inches apart at a depth of 3 inches. /5" _Jl 6-0' 5"- .?■ o • , y 6" JL- A A \ rYeatet/ C/?ecA n \ //e/7t//?a ca&/es 7 i jr -<^ « ' y Cor/r?s ^ Corms '" \ V 6-0" - 7-0"- * /-o" ■* 7"-0" »- Fig. 2. — A, Cross section, and B, plan of heated and cheek beds in the uncovered frame. The heat was first applied on January 14, 1931, and was left on until April 20 (96 days). During this time it was automatically controlled through a thermostat by the temperature in the top 10 inches of soil at a point midway between two legs of a cable loop. The ranges of tem- perature for both soil and air were recorded during the period of heat- ing. They are given in table 1 along with the electrical energy con- sumed. During the heating period, the average range of soil tempera- ture (73° to 80° F) in the heated bed was about 16° higher than in the check bed (58° to 63° F). This difference varied from about 20° during the first few weeks to about 5° during the last weeks. The energy con- sumption averaged 1.19 kilowatt-hours per square yard per day or a total of 114 kilowatt-hours per square yard for the entire heating period. 6 University of California — Experiment Station TABLE 1 Energy Consumption and Kange of Soil and Air Temperatures for Experiments in Uncovered Frame, 1931 Period January 14 to 25 January 26 to February 1 February 2 to 8 February 9 to 15 February 16 to 22 February 23 to March 1 March 2 to 8 March 9 to 15 March 16 to 22 March 23 to 29 March 30 to April 6 April 7 to 13 April 14 to 20 Average Energy con- sumption, kw.-hrs. per square yard per day 1.78 1 50 1 47 89 28 1 65 1 16 1 38 98 1 26 1 04 1 01 64 1.19 Soil temperatures* in heated bed, deg. Fahr. Ay. min. 70 73 74 66 72 74 73 73 75 74 75 73 73 Av. max. 76 75 76 73 79 83 82 82 83 86 86 83 80 Soil temperatures* in unheated bed, deg. Fahr. Av. Av. min. max. 47 50 51 55 54 58 56 60 54 60 55 60 58 65 58 63 62 66 61 66 64 69 67 72 70 80 58 63 Air temperatures around beds, deg. Fahr. Av. min. 36 40 44 44 40 38 38 42 45 39 40 44 45 41 Av. max. 57 59 64 63 62 65 72 67 72 67 77 79 84 68 * The soil temperatures are the average in the top 11 inches of soil. The growth in the heated bed was always considerably more advanced than that in the check bed (fig. 3) . At first the foliage was a light green, but as the season advanced it became normal; and the quality of flowers produced was in no way inferior. In the heated bed, both varieties be- rir Fig. 3. — The upper picture was taken on February 8; the lower on April 28, 1931. The heated plot was consistently earlier in growth and flowering. Bul. 584] Forcing Gladiolus Outdoors with Electricity 7 gan to bloom 5 about two weeks earlier than in the unheated (fig. 4) and had finished before 25 per cent of the latter had bloomed. All the Prince of Wales variety were harvested 25 days before the last spike was cut Pr/oce of Wo/es 5/)0y/or *^ Legend 1 //eat erf 36 c/ayj 7f% ///7/?e0teo' * i »_ 160% \//Z% ^s s 9 /3 ~/c//?e /? r// A/fat/ Fig. 4. — Blooming period of gladiolus in the uncovered frame. Points on the bars indicate dates when 25, 50, and 75 per cent, respectively, of the spikes were har- vested. The figures at the ends of the bars show percentages of spikes harvested in relation to the number of corms planted. on the check plot, while the Shaylor variety showed a difference of 21 days in favor of the heated. The percentage of corms blooming is slightly- in favor of the check plots, but it may not be significant, since the num- ber involved is small. FORCING IN THE OPEN FIELD In 1932, eight beds in the open field, each 18 inches wide and 26 feet long, were used, four being heated and four unheated (fig. 5). In each heated bed a single circuit of 52 feet of soil-heating cable was buried to Corms • • //eat//?? cc?6/es '■"■■'■•' -. . Fig. 5. — Cross section of the heated bed in the open field. a depth of about 5 inches. It was placed in a hairpin loop running the length of the bed with the legs spaced about 12 inches apart. The con- nected load in each bed was about 475 watts, or about 12 watts per square foot. 5 Spikes were considered mature when the first flower opened. 8 University of California — Experiment Station CO O W PQ o ►a w W O w 05 W W P Eh < Pi W Oh w 95 u . 3 95 -wT3 C s3 0>„c o>^ r * u^3 Oj .3 o3 S3 a > 05CClO(MOOOb-00 CO CO CO CO ^ CO ^ *** * m oo b o> e to ^* ^ CO ^ CO ^* ^< 4)73 «- 03 3J2 • 03T3J5 fc 03 s3 tt S3" Saj . 0> e * '"S a S3 s > U)*U5IO!00 03 O t_ ^ ~* JS ^T3 03 ft2 §> *u 93- :3 s3 O CT3 co-~ S3 a to co o —i c» r^ o N 00 X » OO N 00 > < r^coco-r^oococo^r^ooooocooi 0QT3 .2.8*?*, m a o> 5 ?> s3 S g -3 "*- 3T3 £ 8.S8 NN»NM- co «-■ S-d-S S3 +^ hH is * • o> a to ax!j> B^ -S $ 03* X3 >> ."2-03 0.5-0 CO S3 a O0SNN^Tf00!D ^ OB'S .. .2 +s i >> . >>-u S3 •„ , ■Q M a 0) £ 03 S3 fe a-^-^oi 73 C 3T3 95 3 »- m 93 » >> cr » " c _o s3 03 a 8 3*° t - NNNNHHiHHH T3 o 43 Ch 03 u -O o> o ,3 o S3 o o o o CO o » >. 2 >> >> si (O n O n n n o o p o >> S3 % O S3 s3 3 3 3 C S3 S3 ►-s i-s S3 S3 3 3 - - 0) 03 h S3 3 - «0 - i-i rH OJ O M O ^H (M CO S3 s3 s3 s3 cL a a a a o V 4) (b -a o 3 a T3 03 J3 s3 3 S3 03 a o co Bul. 584] Forcing Gladiolus Outdoors with Electricity 9 Six varieties of gladiolus — Rose of 1910, Jack London, Shaylor, Scar- lano, Prince of Wales, and Bothkin — were planted on November 11, 1931. The rows were run across the beds, spaced 8 inches apart; and four corms were planted about 3 inches deep and 4 inches apart in each row. Pose of /9/0 Jack london Shay/or 5car/ano Pr/nce of Wa/es 8o£f?Ain w///, t>//////>////>/ I I lege/70' ^/Veoted /02 days c V///////A f/eat?ed 60 days ■gzzzzz2ztzz2Xt I///// / / / / 7/ , •//// /}///?/;/>;;/; ////////>///;?/;;;; ;;>/;////>///n /?p% //////7 /"/>>> w/sh;/////;/;;7tT* S2% S / S ? J>S f />//????// 3 6/s?/?eoted 7e% 82% ss% 170% 172% 90% ies% 73% ZBZZ2ZBZZZZBZB& S>6% 168% m/os% 7S% 160% /J // 2/ 2S 29 May /o /4 ^St//?e /£ 22 26 30 Fig. 6. — Blooming period of gladiolus in open-field beds. Points on the bars indi- cate dates when 25, 50, and 75 per cent, respectively, of the spikes were harvested. The figures at the ends of the bars show percentages of spikes harvested in relation to the number of corms planted. The current was first turned on in all four heated beds on January 26, 1932. In three it was left on until May 7 (102 days), and in the fourth until March 26 (60 days). The heat was automatically regulated by a thermostat that was controlled by the soil temperature at a point mid- way between the legs of the cable and at the same depth as the corms. The thermostat was set to turn the electric current on at 60° and off at 66° F. Table 2 gives the electrical energy consumed and the temperature range for the various beds during the periods of heating. It shows a very close agreement of the soil temperatures and energy consumption in the heated beds during the first 60 days. The minimum soil tempera- ture during this period averaged 16° warmer than in the unheated bed, whereas during the succeeding 38-day period it averaged 11° warmer. Although soil-temperature readings were not taken after the heat was discontinued in the 60-day bed, in all probability they were the same 10 University of California — Experiment Station as those in the unheated bed for the same period. The energy consumed in the bed heated 102 days dropped from an average of 1.95 kilowatt- hours during the first 60 days to 1.04 during the last 38 days of heating. The blooming periods are shown graphically in figure 6. Of the six varieties planted, three — Jack London, Shaylor, and Prince of Wales — Fig. 7. — View of a heated bed in a covered frame, showing the heating cable in place ready to be covered with 3 inches of soil. After the bulbs were planted, 3 more inches of soil was placed over them. were exposed to both the 60 and 102-day periods of heating. In each instance those receiving the shorter period of heat began blooming be- fore or as soon as those receiving the maximum amount, 75 per cent of Prince of Wales and over 50 per cent of Jack London and Shaylor being harvested before one-fourth of the 102-day plots had bloomed. In all varieties the unheated corms began to bloom from 10 to 22 days later than the heated. The percentage of blooms shows a rather marked difference in some varieties. This was partly caused by a prolonged period of high tem- peratures about the middle of June, when the young buds were so badly scorched that they never recovered sufficiently to produce a normal spike. FORCING IN COVERED FRAMES In 1933 the plantings were made in four 6 x 30-foot outdoor frames, three of which were heated and one unheated. During the first nine weeks of the heating period, all the frames were covered at night and on cloudy days by sash made of wax-impregnated muslin. 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