Root Dipping of Conifer Seedlings 

 Sliows Little Benefit in the Northern 

 Rocky Mountains 



John P. Sloan 



Introduction 



Root dips coat the root systems of bareroot seed- 

 lings with some kind of water-holding or growth- 

 stimulating substance before planting. Foresters 

 have experimented with root dips for many years 

 and they have often been iised when planting. Sloan 

 (in press) describes fo\ir root dip categories and the 

 various types of root dips that have been used on 

 North American conifers: soil slurries, vermioilite or 

 ground sphagnum moss, hydrophilic gels, and other 

 materials, including organic substances, bioregulants, 

 pesticides, and other chemicals. 



Clay slurries and hydrophilic gels have been the 

 most popular root dips. They made their way into 

 reforestation as a means to protect seedlings during 

 storage, to protect seedlings from exposure to drying 

 conditions before planting, and to hold water in the 

 root zone of newly planted seedlings. They have been 

 found to be effective in protecting conifer seedlings 

 against exposure to sun, wind, and other drying con- 

 ditions before planting (Dierauf and Marler 1969, 

 1971; Owston and Stein 1972; Tabor and Davey 1966; 

 Williston 1967), but were detrimental to seedlings 

 d\iring cold storage (Dierauf and Marler 1969; MuUin 

 and Bvmting 1979; Williston 1967). Sloan (in press) 

 reviewed the published results of root-dip studies, 

 finding few studies where root dipping improved the 

 survival and growth of conifer seedlings that were 

 protected against drying. 



In the early 1970'8 the U.S. Department of Agricul- 

 ture, Forest Service's Intermountain Region made 

 root dipping in a vermiculite and water mixture a 

 standard step when preparing bareroot seedlings for 

 planting. Vermiculite absorbs and holds moisture 

 that would otherwise drip off the root system or eva- 

 porate during drying conditions. The Targhee Na- 

 tional Forest used a pump to keep the vermiculite 

 suspended in water. The pump groxmd the vermicu- 

 lite into a slurry that looked, felt, and acted much 

 like clay slurry. Since then, various hydrophilic gels 

 have been tried as root dips throughout the region. 



Intermoimtain planting sites are noted for their hot, 

 dry conditions during the summer months. Root dip- 

 ping was supposed to help moderate the harsh condi- 

 tions. This paper is a report of an investigation into 



the effect of root dipping in vermiculite, vermiculite 

 slurry, or hydrophilic gels on the growth and survival 

 of western conifer planting stock in the Intermoun- 

 tain West. 



Materials and Methods 



Tests took place in growth chambers, in a green- 

 house, and under field conditions. All stock was 2-0 

 (2 years in the n\u*sery bed, years in the transplant 

 bed) bareroot seedlings grown at Lucky Peak Nursery 

 near Boise, ID: ponderosa pine {Pinus ponderosa 

 Dougl. ex Laws.), lodgepole pine (Pinus contorta var. 

 latifolia Engelm.), Douglas-fir (Pseudotsuga men- 

 ziesii var. glauca [Beissn.] Franco), and Engelmann 

 spruce (Picea engelmannii Parry ex Engelm.). For 

 growth chamber and greenhouse tests, seedlings were 

 hand Ufted as soon as niu^ery conditions allowed and 

 stored in plastic bags at 36 °F for 7 days or less. For 

 the field tests, seedlings were lifted and stored in 

 Kraft Poly bags on the National Forest District where 

 they were planted. All stock was dormant, with the 

 exception of the Douglas-fir in the second greenhouse 

 experiment. The poor root growth of that Douglas-fir 

 stock indicated that the seedlings probably broke dor- 

 mancy before they were lifted. 



Measurements 



For new root growth, long and short roots were 

 treated differently. All new roots shorter than 1.5 cm 

 were counted. Most roots in this category were shorter 

 than 0.5 cm. Roots longer than 1.5 cm were counted 

 and measured to the nearest centimeter. The total 

 length of aU new roots was calculated by multiplying 

 the number of short roots by 0.5 cm and adding the 

 sum of aU long roots. An index of mycorrhizal activ- 

 ity was estimated by counting the number of mycor- 

 rhizal root tips on the first 10 cm of the second lateral 

 root from the root collar. 



Shoot heights were measured fix)m the ground line 

 to the tip of the terminal bud, to the nearest centi- 

 meter. If there was no terminal bud, height was 

 measured to the base of the needles nearest the 

 shoot's tip. 



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