DIF Makes A Difference 



A New Technique to Control Plant Development and Height 



Nancy Adams 



Keprintedjrom an article by Nancy 

 Adams, Extension Educator, Rocking- 

 ham County, in the UNH Cooperative 

 Extension Ornamentals Update, 

 Spring 1991. 



Research is beingconducted at Michi- 

 gan State on the use of temperature to 

 control plant height. Dr. Royal Heins 

 and his associates have discovered 

 that height can be controlled or regu- 

 lated by the "DlF"erence between 

 day and night temperatures. Growers 

 have traditionally kept greenhouses 

 wanner during the day than at night 

 and it is now known that this practice 

 will produce taller plants than will a 

 regime of cooler days and warmer 

 nights. It is also known that changing 

 the absolute temperature, yet main- 

 taining the sameday/nightdifference, 

 will affect plant maturity. 



DIF is defined as the mathematical 

 difference between the day tempera- 

 ture (DT) and the night temperature 

 (NT): DIF equals DT minus NT. If the 

 night temperature is higher than the 

 day's, the DIF value would be a nega- 

 tive one. 



Plants grown under equal DIF" values 

 have a similar final height, although 

 the rate of maturity will differ with 

 different temperature regimes. For 

 example, plants grown at a day/night 

 temperature of 75 will be the same 

 heightas, yet more mature than, plants 

 grown at a day/night temperature of 

 70. 



As the positive DIF number increases, 

 the height ofthe plant increases. The 

 reverse is also true. Plants become 

 shorter as the day temperature be- 

 comes cooler relative to the night 

 temperature. 



Obviously, using DIF in a working 

 greenhouse could be somewhat com- 

 plicated. Michigan State has worked 

 out a method of charting or graphing 

 the desired growth of selected potted 

 plants such as poinsettias and Easter 

 lilies. A computer program can take 

 your desired flowering date, combine 

 this vrith the desired finished plant 

 height, and print out a growth chart 



specificallytailoredtoyourcrop. Dur- 

 ing the growing season, the height of 

 the crop is measured and then plotted 

 on the graph. If it falls above or be- 

 low the ideal range, the grower can 

 accelerate or slow the growth by alter- 

 ing the DIF temperatures. 

 With this system, apparently it is pos- 

 sible to decrease the use of growth 

 regulators and rely more on tempera- 

 ture controls to maintain ideal plant 



growth and height. 

 The magazine Greenhouse Grower 

 has compiled a series of articles con- 

 cerning DIF. Their 36-page booklet 

 entitled Control Plant Growth With 

 Temperature costs $12.00 and can be 

 obtained by writing: Greenhouse 

 Grower, 37733 Euclid Avenue, 

 Willoughby, Ohio 44094. Telephone: 

 (216) 942-2000; FAX: (216) 942-0662. 



North Country Product Compost 

 Gains Acceptance in New Hampshire 



Jay Kilbourn 



Oack in the days before chemical 

 fertilizers, the value of a good com- 

 post was well understood here in New 

 England. To this day in other parts of 

 the world, "night soil" (or human 

 waste) is utilized extensively, albeit 

 without adequate sanitation precau- 

 tions, in agriculture as one ofthe only 

 sources of plant nutrients and organ- 

 ic matter available. Now the State of 

 New Hampshire is taking steps to re- 

 vive an old practice and protect public 

 health. 



In a new effort to evaluate and utilize 

 recycled products, the Department of 

 Trasnsportation has approved North 

 Country Products Compost and other 

 soil amendments for utilization on the 

 state roadways. At the same time, the 

 legislature is actively considering a 

 new definition for compost in its solid 

 waste laws. Feedstocks now included 

 in the definition of compost include 

 manures, municipal solid waste, sew- 

 age sludge, leaf and yard debris, and 

 other organic wastes. The State is also 

 redrafting all regulations relative to 

 the manufacture and distribution of 

 compost derived from any organic 

 waste material. 



Among the many benefits of composts 

 are: 



«■ high organic content yielding 



high erosion control, 

 «' the ability to provide plant nutri- 

 ents over the long term, 

 «■ the use as an ideal lopsoil substi 

 tute when mixed with silty sand, 

 « low cost relative to conventional 

 erosion control products and na- 

 tive loam. 

 According to Revin I^ngston,the 

 Plant Manager at l^banon's Compost 

 Facility, "We used to incinerate our 

 wastewater sludge just to solve a 

 waste problem. Then we sent the ash 

 to the landfill. Now we manufacture 

 compost, a valuable resource for our 

 community, and receive a little rev- 

 enue for the town." 

 This is a good year for all of our New 

 Hampshire plantsmen and women to 

 support our municipalities and busi- 

 nesses in this recycling effort. North 

 Country Products compost specialists 

 are available to provide technical in- 

 formation about their products and 

 about compost utilization in general. 

 Call them at 536-5280. 



Jay Kilbourn is Group Manager of 

 Resource Conservation Services, Inc., 

 Compost and Processed Products 

 Division. ^ 



June/July 1991 19 



