Reprinted from Tree Planters' NotesVol. 23, No. 3, Aug. 1972, pp 22-26

Late lifting and freezing in plasticbags improve white spruce survivalafter storage

THIS FILE COFY D. Hocking' and B. Ward'MUST BF RETURNED TO:

NFORMATION SECTION,ORTHERN FOREST RESEARCH320-122 STREET, CENTRE,LIMONTON, ALBERTA,6H 395

Overwinter storage of conifer seedlings is useful for various reasons, buttwo compelling ones at the Alberta Provincial Tree Nursery (Edmonton,Alberta) are to reduce the spring workload and improve inventory accuracyfor planning of planting schedules. This article reports studies of severalpackaging methods and storage at sub-freezing temperature for whitespruce.

A 1966 trial showed that survivalof conifer seedlings after storage at34° to 36°F. was improved by de-laying lifting until Oct. 24 whencompared with lifting (1) up to amonth earlier. A recent publica-tion describes successful long termstorage of red pine frozen in plas-tic bags (6).

We planned to lift 3-0 whitespruce (Picea glauca (Moench)Voss var. albertiana (S. Brown)Sarg.) weekly from October 13 toNovember 3, 1969. Inclementweather prevented lifting duringthe last 2 weeks, so stock for thistrial was lifted on only October 13and October 20.

Methods

Before packaging, seedlings weregraded and culled to a mean heightof about 8 inches, counted intobundles of 50, and root-dipped inwater to remove excess soil.

Six packaging methods weretested with five replicates of 50seedlings for each method:

1. Heeled-in in peat. (Rootswere loosely packed in moist

peat in wooden flats, tops ex-posed.)Jelly-roll bales. (Seedlingswere rolled up root-to-root,with peat moss, in a plasticand burlap wrapper, tops ex-posed.)Plastic (polyethylene) bags,with moist peat. (Seedlingswere placed root-to-root, ly-ing horizontally in the bags,roots covered loosely withmoist peat. The bags werethen sealed by folding andstapling the tops.)Plastic bags, with steamedpeat. (The same as method3, but the peat was steamedfor 3 hours at 185°F. in anattempt to reduce mold inoc-ulum.)Plastic bags, no peat. (Thesame as method 3, but with-out peat.)

6. Current Alberta Tree Nurs-ery method. (Essentiallysimilar to method 3, but larg-er bags are used and are cov-ered with burlap to improvemechanical strength for ship-ping.)

Plants were packaged and plac-ed in storage on racks with goodair circulation on the day of lift-ing. Storage was at a nominal25°F. Daily monitoring of themaximum-minimum thermometerindicated fluctuations of up to ±5°F., but generally within 2°F.On eight individual, widely-sepa-rated days maximum readings wereabove 32°F. On April 20, controlswere raised to 32°F. to start thethawing process, and monitoringafter that date indicated fluctua-tions of up to 4°F. Humiditywas not controlled or monitoredbecause instruments were not avail-able, but the presence of moistpeat on the floor and racks ensuredrelatively high levels.

Samples of 10 seedlings weretaken from each packaging methodat roughly monthly intervals dur-ing storage, and moisture contentsand presence of starch in tops and

'Research Scientist, Canadian ForestryService, Edmonton, Alberta, Canada.

'Horticutural Technician, ProvincialTree Nursery, Edmonton, Alberta, Can-ada.

TABLE 1.-Survival of white spruce seedlings stored frozen overwinterusing different packaging methods

(Figures in the same column followed by the same letters do not differsignificantly at the 1 percent level. Basis: five replicates of 50 seedlingsper treatment; Duncan's multiple range test.)

Packaging Method

Heeled in peatJelly-roll balesPlastic bags with moist peatPlastic bags with steamed peatPlastic bags without peatCurrent nursery practiceCheck (lifted May 19)Mean, all methodsMean, method 1 and 2Mean, method 3, 4, 5, & 6Mean, method 3, 4, & 6

Survival when lifted onOct. 13 Oct. 20 Mean

(both dates)

Percent

1.2 a 11.6 a 6.4 a

16.0 b 46.8 b

31.4 b

37.6 c 64.0 c 50.8 c

47.2 c 58.1 be 52.6 c

77.0 d 87.3 d

82.2 d

49.2 c 79.7 c d

64.5 c

97.0 e 97.0 e 97.0 e

34.8 58.08.6 29.2

52.4 72.344.7 67.3

roots were determined. Moisturecontent was determined by differ-ence in weight after drying at100°C. for 24 hours. Presence ofstarch was visually quantified afterfreshly cut sections of stems androots were dipped into 1 percentiodine in 2 percent aqueous potas-sium iodide.

All the stored seedlings werehand-planted in the nursery dur-ing the period May 11-15, 1970.On May 19, 250 check seedlingsfrom the same nursery plot werelifted and planted. All seedlingswere irrigated and weeded.

Survival was tallied on June 29.(Trees were counted living if theyhad initiated new top and rootgrowth.)

Results

Survival rate of seedlings storedin plastic bags without peat wassignificantly higher than in anyother methods but significantlylower than among freshly-dugchecks. Survival rate in each meth-od was higher for seedlings liftedOctober 20 than for those liftedOctober 13 (table 1).

Moisture content (fig. 1) of seed-lings with tops exposed (methodsI and 2) declined progressivelythroughout the storage period,more rapidly at first from tops, butlater more from roots. This un-even moisture change was also ob-served by Tarrant (8) from seed-lings in bundles. However, seed-lings totally enclosed in polyethy-lene bags lost no moisture or elsegained moisture, and there wereno important differences betweentops and roots or among methods3, 4, 5, and 6.

Starch content, determined bythe iodine test, consistently de-creased with increasing durationof storage. This trend was moremarked in seedlings lifted on theearlier date and in seedlings stored

with tops exposed, but no seed-lings were totally without starchon May 11. Some seedlings liftedOctober 13 and stored in heeledin peat had no detectable starch intops by March 20, but roots stillstained deep blue.

Discussion

In the Alberta nursery, as inother northern nurseries, it is oftendifficult to postpone fall liftingbeyond the end of October, lead-ing to a need for overwinter stor-age of 6 months or more. In thistrial, storage was for 7 months.The present results confirm andextend knowledge of the beneficialeffects of late lifting, in improvedsurvival after storage. The benefitsprobably result from reducing theduration of artificial storage andfrom ensuring more complete dor-mancy of the planting stock, as in-dicated by less rapid depletion ofstarch reserves in stock lifted atthe later date, and borne out byimproved survival rates. Similarcorrelation was observed by Hell-mers (3).

Grouping the survival data intomethods totally enclosing the seed-lings and those with tops exposedconfirms the need for stringent pre-cautions against desiccation. Seed-lings stored with tops exposed re-tained considerable starch reserves,but had lost moisture to near orbelow levels found to be critical inother studies (2). In this study,too, desiccation during storage wasapparently the primary cause ofmortality.

Slayton (7) reports successfulstorage of white spruce in open-topped bales, at 28°F. and 97 to100 percent relative humidity. Des-iccation of bales in the presentstudy may result from failure tocontrol humidity and the ratherbroad temperature variation. How-ever, the ease of packaging in to-tally enclosed systems, such as mul-ti-walled kraft paper bags withpolyethylene liners, and the bet-ter results obtained with such sys-tems, lessen the need for humiditycontrols on the whole building.

Molding of foliage, a principalcause of losses in stock stored at

F.20 M.20

1970

0.20 N.20

1969

A.20 M.20

0 0 Treatments 3,4,58 6, roots & tops

A A Treatment 2, tops

4 A Treatment 2, roots

q q Treatme nt 1, tops

Treatment 1, roots

4

Date of Sampling

temperatures above freezing (4),was almost wholly absent in thisstudy; a result no doubt attribut-able to lower storage-temperature.

Since both molding and desic-cation were controlled when seed-lings were stored frozen in plasticbags, the question arises: Why didso many seedlings die? Check seed-lings left in the ground all wintershowed 97 percent survival ratewhereas the mean of the plastic-bag methods lifted on October 20was 72 percent. Temperatures pre-vailing under snow cover duringthe winter are usually in the samerange of 20° to 32°F., so the causesof mortality cannot be simply de-pendent on temperature. The an-swer must lie in other physiologi-cal changes taking place in stored

seedlings, not detectable by therather crude starch-staining iodinetest.

Another curious observation isthe effect of peat in methods 3, 4,and 6. Mean survivals in thesemethods were 33 and 20 percentless for the two lifting dates thanin method 5, which was withoutpeat. Similar observations weremade recently by Lindquist (5).Possible reasons for this differencemight be microbiological activityor toxins in the peat leading toroot damage, but no evidence tosupport this is available.

Conclusions

From the present results, whitespruce may be stored for 7 months

Figure 1.-Moisture depletion from whitespruce seedlings with duration of storagein various packaging methods,

if the following conditions aremet:

The seedlings are dormant,achieved by late lifting.Desiccation is prevented bypackaging in plastic bags. Noadded peat or other moisture-retaining materials are nec-essary.

3. Molding and metabolic activ-ity are minimized by storageat sub-freezing temperature.

Literature CitedChedzoy, J.1967. Storage requirements for nursery

stock. In: Proc. Intermountain Nur-seryman's Assoc. Annu. Meeting, In-dian Head, Sask., Aug. 1967: 66-68.

Faulkner, R. and J.R. Aldhous.1958. Handling of plants. Rep. Forest

Res., Forest Comm. Lond., 34-36.Hellmers, H.1962. Physiological changes in stored

pine seedlings. Tree Planter's Notes53: 9-10.

Hocking, D.1972. Effect and characteristics of

pathogens on foliage and buds ofcold-stored white spruce and lodge-pole pine seedlings. Can. J. ForestRes. 1 (4):208-215.

Lindquist, C. H.1970. Plant storage studies. 1969 Sum-

mary Rept., Tree Nursery, P.F.R.A.,Indian Head, Sask., Can. : 17-18.

Mullin, R. E. and W. R. Bunting.1970. Frozen overwinter storage for

red pine. Tree Planters' Notes 21(4): 15-17.

Slayton, S.H.1970. Storing baled red pine, black

spruce, and white spruce over winterfeasible in upper Michigan. TreePlanters' Notes 21 (4): 15-17.

Tarrant, R. F.1964. Top and root moisture content

of stored Douglas-fir planting stock.U.S. Dept. Agric. Forest Service, Res.Pap. P.N.W.-13: 1-8.