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5-1987 Evaluation of Three Coverings for the Overwintering of Container Grown Herbaceous Perennials in Kentucky Richard Beckort Western Kentucky University
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Richard Leland
1987 EVALUATION OF THREE COVERINGS FOR
THE OVERWINTERING OF CONTAINER
GROWN HERBACEOUS PERENNIALS
IN KENTUCKY
A Thesis
Presented to the Faculty of the Department of Agriculture
Western Kentucky University
Bowling Green, Kentucky
In Partial Fulfillment
of the Requirements for the Degree
Master of Science
by
Richard Leland Beckort
May 1987 AUTHORIZATION FOR USE OF THESIS
Permission is hereby Library to /71 granted to the Western Kentucky University microfilm or other make, or allow to be made photocopies, or scholarly copies of this thesis for appropriate research purpo sea.
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p•45 t•onl Mos •undik ..PiS 61 3 72, EVALUATION OF THREE COVERINGS FOR
THE OVERWINTERING OF CONTAINER
GROWN HERBACEOUS PERENNIALS
IN KENTUCKY
RertNommended A9 /9'79-- (Dat4)
a#1442- 91,/ Direct r of Thesis
1 -••••/
Approved z2Jr / 7 el 1e)' 4/24-4
Dean of the Graduat ACKNOWLEGEMENTS
would like to express my appreciation to t e following:
Dr. James M. Martin for his advice and assistance during my graduate study and in preparation of this thesiN.
Dr. James P. Worthington for his advice in plPHitind this thesis and for serving as a member of thp ,iridoatp committee.
Dr. Ray E. Johnson for his suggestions and tor serving as a member of the graduate committee.
Ellen justiss for her encouragement and assistance in the preparation of this thesis.
My family for their support thoughout my study at Western
Kentucky University.
iii TABLE OF CONTENTS
PAGE
INTRODUCTION
REVIEW OF LITERATURE 3
MATERIALS AND METHODS 6
RESULTS AND DISCUSSION 9
CONCLUSIONS 18
APPENDIX 19
LITERATURE CITED 21
iv LIST OF TABLES
PAGE
Table 1. Average ratings for the blocks of herbaceous perennials overwintered under different coverings, 1986 10
Table 2. Average ratings for varieties of herbaceous perennials overwintered under different coverings, 1986 11
Table 3. Average ratings for locations under different overwintering coverings, 1986 17 LIST OF FIGURES
PAGE
Figure 1. Variety by cover interaction: (A) Achillea filipendulina 'Cloth of Gold', (B) Achillea millefolium 'Cerise Queen', (C) Chrysan- themum coccineum 'Double Mixture', (0) Chrysanthemum parthenium 'Ball Double White Improved' 1 3
Figure 2. Variety by cover interaction: (E) Coreopsis lanceolata 'Double Sunburst',(F) Coreopsis lanceolata 'Sunray', (G) Gaillardia x qrandiflora 'Burgundy', (H) Geum quellyon 'Mrs. Bradshaw' 14
Figure 3. Variety by cover interaction: (I) Gypsophila paniculata 'Paniculata Single', (3) Heuchera sanquinea 'Bressingham Hybrids', (K) Kniphofia uvaria 'Royal Castle Hybrids', (L) Myosotis sylvatica 'Victoria Blue' . . 15
vi EVALUATION OF THREE COVERINGS FOR THE OVERWINTERING OF CONTAINER GROWN HERBACEOUS PERENNIALS IN KENTUCKY
Richard Leland Beckort May 1987 22 pages
Directed by: Or. James Martin, Dr. James Worthington, Dr. Ray Johnson
Department of Agriculture Western Kentucky University
The purpose of this study was to evaluate three coverings for overwintering twelve varieties of container grown herba- ceous perennials under Kentucky conditions. The twelve peren- nial varieties were started from seed in the spring and had been moved to one gallon containers by fall. In the first week of December, three blocks of containers were covered with one of the following: one layer of 4 mil, milky copolymer; one layer of quarter inch microfoam and one layer of milky copolymer; a sandwich of two layers of milky copolymer with
6 inches of wheat straw between them; the remaining block was left uncovered as a check.
The perennials were uncovered in the spring, observed, and evaluated. The single layer of copolymer and the micro- foam and copolymer treatments had the most new growth. The growth under the copolymer and straw sandwich method was elongated and white. Only three containers in the uncovered treatment showed signs of regrowth.
The microfoam and copolymer and the single layer of milky copolymer proved to be the best coverings for the over- wintering container grown herbaceous perennials in Kentucky.
vii INTRODUCTION
Herbaceous perennials have been an inportant part of the flower garden throughout nistory. In recent years, a tremen- dous increase in the popularity of perennials has occurred.
Hundreds of new cultivars are now being produced by the com- mercial grower. Along with the change in the number of peren- nials being produced has come a change in the method of pro- duction. The trend is moving from field production to con- tainer grown stock, which presents some problems that the grower must overcome.
Overwinterind container groan stock for sale in the spring has been a serious problem. Field groan perennials are left in the around and carried-over similar to plants that are planted in a garden setting, a fairly inexpensive method of overwintering the perennials. These plants are insulated by the soil. The problem with container grown stock is that they lack adequate insulation. If left unpro- tected during winter, the soil ball will freeze, killing the roots and the plant. They could be overwintered in a green- house, but that procedure is expensive.
As an alternative to greenhouses, growers in different areas of the country are using several methods of covering perennials for winter protection. The type of covering depends on the climatic conditions of the area and the 2
hardiness of the plants being drown. Plants grown in colder climates need more winter protection than those grown in milder climates.
This is a study of overwintering container grown peren- nials in South Central Kentucky. Several herbaceous peren- nial taxa and coverings were used to determine whether there is one covering that is best overall for a wide variety of taxa in this area. It was also designed to determine whether, of those tested, there are some taxa that require more pro- tection than others. REVIEW OF LITERATURE
Plant roots growing in the soil are protected from the
freezing temperatures of winter; the earth's own internal
heat ant insulation protect the roots from freezing injury.
Plants lose this protection when they are grown in containers
that are kept above the soil line.(4) This winter protection
is lost because the root bail of the plant does not have
heat-retaining ability equal to the soil, partly due to the
root ball's increased surface area.(6) The soil and roots
in these containers are subjected to ambient temperatures,
damaging the roots which are less cold hardy than the upper
portions of tne plant.(4)
Over the last decade, the most widely used nursery prac-
tice to overwinter container grown stock has been to use white
polyethylene hoop houses with minimal cr no heat.(10) A hoop
house is a small greenhose-like structure. The frame is built
of lightweight pipe bent into arches. These arches are anchor- ed in the ground and covered with one or two layers of poly- ethylene film. The ends of the house are then enclosed with either polyethylene film or plywood. These hoop houses offer excellent protection to container stock; however, their being so expensive, has lead to the introduction of many new methods for overwinterino container grown plants.(2)
The method now being used is to place the containers in
3 4
a bed and cover them with a plastic sheet of some type. This
cover is usually one or two layers of clear or milky poly-
ethylene film.(1,2,4,6,10) One method that has been used
with great success in the northern regions of the country
has been the use of a sandwich of two layers of milky poly
with 6-12 inches of straw between them.(7) This method has
given excellent protection in studies by Perry at the Univer-
sity of Vermont. The temperatures under this type of cover
never fell below 0 degrees C, even when the outside temper-
ature fell to -23 degrees C.(12)
Gouin at the University of Maryland has conducted
research using microfoam to overwinter container grown nursery
stock.(5) Microfoam is a flexible, white, polypropylene foam
material that is manufactured by Dupont. It is composed of
fifty thousand closed air cells per cubic inch and has a
layer of milky polyethylene bonded to one side. It is avail- able in either one-eighth or one-quarter inch thickness.
Microfoam does not support the growth of mildew, fungus, or bacteria.(14)
Before the container grown plants are covered they should be thoroughly watered. If the soil mix dries out during the winter, then the plant will die of drought stress.(7) A water saturated root ball frezes slower than a dry root ball.
When water freezes it gives off heat, which helps mantain the temperature under tne covering.(14) The high moisture level and the enclosed conditions of this system increase the risk of disease. Botrytis is one of the major disease 5
problems. A spray of Benlate, Botran, or Daconil with a spreader sticker should be made about two weeks before cover- ing to help control the disease problem.(6,13) Mice and other rodents can be a problem under the coverings. They burrow through the soil and feed on the roots of the plant. To control this problem, rat bait should be placed on the ground between the pots before covering.(6)
The plants should be covered in the fall after they have gone dormant and the tops have been frosted down. The covers should be removed as early in the spring as possible.(3,8)
Any new growth cnder the covers, will be very tender and could be seriously damaged by temperatures below 0 degrees
C.(1) A white poly cover delays growth in the spring, as compared to a clear cover, therefore allowing the plants to stay covered until warmer temperatures occur later in the spring.(6) MATERIALS AND METHODS
Research was conducted on tne Western Kentucky University
Farm in Bowling Green, Kentucky from March 1985 to May 1986
to evaluate different methods of overwintering container
grown herbaceous perennials. Three different coverings were
evaluated for their winter protection of twelve different
varieties of herbaceous perennials.
The following twelve perennial varieties were used in
the research: Achillea filipendulina 'Cloth of Gold', Achillea
millefolium 'Cerise Queen', Chrysanthemum coccineum 'Double
Mixture', Chrysanthemum parthenium 'Ball Double White
Improved', Coeropsis lanceolata 'Double Sunburst', Coreopsis lanceolata 'Sunray', Gaillardia x qrandiflora 'Burgundy',
Geum quellyon 'Mrs. Bradshaw', Gypsophila paniculata
'Paniculata Single', Heuchera sanquinea 'Bressingham Hybrids',
Kniphofia uvaria 'Royal Castle Hybrids', and Myosotis sylvatica
'Victoria Blue'. With these varieties, the coverings were tested over a wide range of cultural requirements and differ- ent hardiness ratings. The perennials were started from seed in the early spring of 1985 and then transplanted into cell packs. The perennials were transplanted into 6-inch standard plastic pots in the late spring. During the last week of
September the plants were moved to one gallon plastic Zarn- tainer 400 brand containers.
6 7
The soilless mixture used in all potting operations was
Premier Pro-Mix BX, which is a mixture of peat moss, vermicu- lite, perlite, dolomitic limestone, super phosphate, potassium nitrate, non-ionic wetting agents, and fritted trace elements.
The plants were fertilized with a constant liquid feed program using Peter's brand 20-20-20 soluble fertilizer. The fertilization was stopped the last week of October.
Forty-eight containers of each variety were moved outside to a grave]ed area during the last week of October 1985.
They were arranged into three blocks with each block contain- ing four different treatments. Each treatment consisted of four rows of plants. Each row had twelve containers, one of each iariety, randomly arranged. The forty-eight containers in each treatment were set pot-to-pot to help insulate and decrease the air space. Each treatment covered an area that was approximately 2f feet wide and 7 feet long. The treatments were 5 feet apart.
On December 2 and 3, 1985, the top growth of the peren- nials was cut off to within one inch of the soil line to decrease the chances of disease problems. The organic matter is a excellent harbor for pathogen growth. The containers were then watered thoroughly to ensure adequate moisture throughout the winter. To control any rodent problem, three
50 mg packages of Havoc brand rat bait were placed in each treatment. The treatments were then applied. Treatment 1 was left uncovered as a control. Treatment 2 was covered with one layer of 4 mil, milky co-polymer. Treatment 3 was covered with one layer of one-quarter inch microfoam and one layer of 4 mil, milky copolymer. Tne polyethylene layer on the microfoam was placed facing up. Treatment 4 was covered with one layer of 4 mil, milky copolymer, 6 inches of wheat straw, and then another layer of 4 mil, milky copolymer. A trench was dug around each treatment in which the edges of the copolymer were placed. The trenches were then refilled to hold the copolymer in place.
On March 17, 1986, the plants were uncovered and overall observations made on the condition of the different treatments.
The plants were then moved into a heated poly greenhouse to speed up the regrowth process. On May 6, 1986, the perennials were given an evaluation of 0, 1, or 2. An evaluation of 0 was given to plants that were dead. An evaluation of 2 was given to plants that were healthy, saleable plants. An eval- uation of 1 was given to plants that were alive but not in saleable condition. RESULTS AND DISCUSSION
The perennials were uncovered on March 17, 1986, and a visual difference could be seen among the four treatmants.
The perennials covered with a single layer of milky copoly- mer and with a layer of copolymer and microfoam had the most new growth. The growth was healthy and green. Those covered with the sandwich of milky copolymer and wheat straw had less new growth; that growth was elongated and whitish in color. This color was due to less light being transmitted through tne thicker coverings which in turn caused the plants to warm up more slowly. In this treatment the slug population was very high. The containers were saturated with water, and there were signs of rotting on some plants. The group of uncovered perennials used as a check had only three containers witn new growth. In the remaining containers, the plants appeared dead. There were no signs of rodent problems in any of the treatments.
There was a significant difference between the ratings of the blocks (Table 1). Blocks 1 and 2 had significantly higher ratings than block 3. This difference was attributed to the orientation of the blocks to the surrounding physical features (buildings, trees, shurbs) and to the prevailing winds in the area.
9 10
Table 1. Average ratings for the blocks of herbacec_s peren- nials overwintered under different coverinos, 1986.
BLOCK NUMBER AVERAGE
1 1.000 a
2 0.990 a
0.844 b a Means followed by the same letter are not significantly different at the 5% level by Duncan's multiple range test.
There was a significant difference in the ratints of the varieties studied (Table 2). Achillea millefolium 'Cerise
Queen' and Coreopsis lanceolata 'Sunray' had significantly higher ratings than Geum quellyon 'Mrs. Bradshaw', Coreopsis lanceolata 'Double Sunburst', Gypsophiia paniculata 'Panicu- lata Single', Chrysanthemum coccineum 'Double Mixture',
Achillea filipendulina 'Cloth of Gold', Gaillardia x qrandi- flora 'Burgundy',Chrysanthemum parthenium 'Ball Double White
Improved', Heuchera sanguinea 'Bressinonam Hybrids', and
Myosotis salvatica 'Victoria Blue'. Knipnofia uvaria 'Royal
Castle Hybrids' and Geum quellyon 'Mrs. Bradshaw' hat significantly higher ratings than Achillea filipenculina
'Cloth of Gold', Gaillardia x qrandiflora 'Burgundy',
Chrysanthemum parthenium 'Ball Double White Improve',
Heuchera sanguinea 'Bressingham Hybrids', and Myosotis sylvatica 'Victoria Blue'. Coreopsis lanceolata 'Double Sun- burst' had a significantly higher rating than Gaillardia x qrandiflora 'Burgundy', Chrysanthemum parthenium 'Ball Double 1ahle 2. Average ratings for varietie of herbace;.)w,- perennials overwintered under diffPrent f:nverings, 1986.
COVERING .r0,1 1- 1Y VARIETIA1 POLY-MICPOCOAM 04 12 IRAW-P01. UNCOVFRED AvERAGF
millefolium 1.833 2.000 1.4 1 7 0.750 1.500 a Isc. Queen'
LorenpAs lanceolata 1.917 2.000 1.833 0.167 1.479 a 1 "--0nT y
Kniphofia uvaria 7.000 1.500 1.500 0.000 1.250 ab 'Royal Castle Hybrids'
Gr'!r1 2.000 2.0U1J 0.750 0.000 1.188 b ."".
COrenp,iS 11n(:e01ata 1.833 1.667 0.717 0.000 1.104 be Thnhutt. r;ypfflhila uniculata 1.500 0.917 1.83i 0.000 LOA; bcd 'vani.ulata SingT,.77 ihrLsanthemum coccineum 1.833 1.500 0.667 0.000 1.000 bcd Mivture'
i_flAtfilirendulina 1.7s0 1.593 11.167 0.0110 0.87s cd hft, of G^Id.
v aLandiflora 1.167 1.000 1.083 (1.004) 0.813 de
Ch_rjsanthemum orthenium 1.000 1.167 0.167 ()moo 0.583 e °111 Dhl. White Improved' heAchera anguinea n.7.0 9.000 0.000 0.313 f .pHlham mlocotis sylvatica 0.000 0.500 11.,(Lr 0.167 0.167 f 'elv..tnria Blue'
,f f:nerIngs 1.465 1.319 a 0.901 h 0.090 c a fillnwed by the same letter are not significantly. dift rent st the 5% level by Duncan's multiple range 12
White Improved', Heuchera sanquinea 'Bressingham Hybrids',
and Myosotis sylvatica 'Victoria Blue', Gypsophila paniculata
'Paniculata Single', Chrysanthemum coccineum 'Double Mixture'
and Achillea filipendulina 'Cloth of Gold' had significantly
higher ratings than Chrysanthemum parthenium 'Ball Double
White improved', Heuchera sanquinea 'Bressingham Hybrids'
and Myosotis sylvatica 'Victoria Blue'. Gaillardia x qrandi-
flora 'Burgundy' and Chrysanthemum parthenium 'Ball Double
White Improved' had significantly higher ratings than Heuchera
sanquinea 'Bressingham Hybrids' and Myosotis sylvatica
'Victoria Blue'.
There was a significant difference between the four
treatments (Table 2). The copolymer and the microfoam treat-
ment and the single layer of milky copolymer treatment had
significantly higher ratings than the copolymer and straw sandwich method and the uncovered treatment. The copolymer and straw sandwich method had a significantly higher rating than the uncovered treatment.
Six perennial varieties had their highest rating when covered with a single sheet of 4 mil, milky copolymer and a layer of microfoam (Figure 1-3). These varieties were
Kniphofia uvaria 'Royal Castle Hybrids', Coreopsis lanceolata
'Double Sunburst', Chrysanthemum coccineum 'Double Mixture',
Achillea filipendulina 'Cloth of Gold', Gaillardia x qrandi- flora 'Burgundy', and Heuchera sanquinea 'Bressingham Hybrids'.
Geum quellyon 'Mrs Bradshaw' did equally well under both a single layer of milky copolymer and the copolymer-microfoam A B C D A B CI D A B C Hi B ONCOVERE, CO-POLYMER POLY-MICROF0Am POLY -STRAW-POLY
Figure 1. Variety by cover interaction: (A) Achillea filipendulina 'Cloth of Gold', coccineum 'Double (B) Achillea millefolium 'Cerise Queen', (C) Chrysanthemum 1/4.4 Mixture', (0) Chrysanthemum parthenium 'Ball Double White Improved'. rd UNCOVERED CO-POLYMER POLY-MICROFOAM POLY-STRAw-POLY
Figure 2. Variety by cover interaction: (E) Coreopsis lanceolata 'Double Sunburst', (F) Coreopsis lanceolata 'Sunray', (G) Gaillardia x prandiflora 'Burgundy', (H) Geum quellyon 'Mrs. Bradshaw'. ••••••••••••••16
UNCOVERED CO-POLYMER POLY-MICROFOAM POLY-STRAW-POL
Figure 3. Variety by cover interaction: (I) Gypsophila paniculata 'Paniculata Single', (3) Heuchera sanguinea 'Bressingham Hybrids', (K) Kniphofia uvaria 'Royal Castle Hybrids', (L) Myosotis sylvatica 'Victoria Blue'. 16
treatment. Achillea millefolium 'Cerise Queen', Coreopsis
lanceolata 'Sunray', Chrysanthemum parthenium 'Ball Double
White Improved', and Myosotis sylvatica 'Victoria Blue' had
their highest rating when covered with a single layer of 4
mil, milky copolymer. Gypsophila paniculata 'Paniculata
Single' was the only cultivar to receive its highest rating
when covered with the copolymer and straw sandwich method.
There was a significant difference between the ratings
of the locations (Table 3). The outside row had a signifi-
cantly higher rating than the inside row. This pattern was
true for all treatments except for the uncovered treatment.
In the uncovered treatment, the inside row nad a slightly
higher value than the outside row. This difference was attri-
buted to the winter conditions which caused the soil ball
of the outside containers to freeze more said. The inside
containers were insulated from the cold by the outside row
of containers. With the research that was conducted for this
study, the differences between the inside and outside rows, in the three remaining treatments, cannot be attributed to a specific factor. There is a need for further research in this area to determine what those factors are. 17
Table 3. Average ratings for locations under different overwintering coverings, 1986.
LOCATION COVERING COVERING AVERAGE OUTSIDE INSIDE
Poly-Microfoam 1.500 1.431 1.464 a
Co-polymer 1.347 1.292 1.319 a
Poly-Straw -Poly 1.097 0.708 0.903 b
Uncovered 0.083 0.097 0.090 c
Location Average 1.007 a 0.882 b a means followed by the same letter are not significantly different at the 5% level by Duncan's multiple range test. CONCLUSIONS
Of the four methods tested, the best for overwintering
a wide variety of container grown herbaceous perennials in
Kentucky is to cover the plants with one layer of quarter
inch microfoam and then one layer of 4 mil, milky copolymer.
This method had the highest rating at 1.465. If a certain
variety of perennial is to be overwintered, then a different
method may need to be used. For example, if Gysophila
paniculata 'Paniculata Single' is to be overwintered, then
a method that provides more protection-- such as the copolymer
and straw sandwich method-- should be used. This variety is
one that might be economically overwintered in a hoop house
or greenhouse. If a variety like Chrysanthemum parthenium
'Ball Double White Improved' or Myosotis sylvatica 'Victoria
Blue' is to be overwintered, needed then is a method that does not offer the plant as much insulation. A single layer of 4 mil, milky copolymer is the method best suited for these
varieties. Container grown perennials can be overwintered in
Kentucky, but the method selected must be suited to the
varieties of perennials that are to be overwintered.
18 APPENDI X
19 20
Table 1. Analysis of variance for the rating of the perennial varieties.
Source of Varition df SS MS
Total 575 548.222 Model 111 358.583 3.230 7.90* Block L 2.930 1.465 3.59* Cover 3 164.625 54.875 134.27* Cover*Block 6 3.000 0.500 1.22 Location 1 2.250 2.250 5.51* Cover*Location 3 3.486 1.162 2.84* Block*Location 2 0.792 0.396 0.97 Cover*Block*Location 6 1.972 0.329 0.80 Variety 11 93.431 8.494 20.78* Cover*Variety 33 70.000 2.121 5.19* Variety*Location 11 5.458 0.496 1.21 Cover*Variety*Loc. 33 10.639 0.322 0.79 Error 464 189.639 0.409
*Significant at the .05 level. LITERATURE CITED
1. Beam, James. 1983. Overwintering plants in containers. p. 56-58. In: Elton m. Smith (ed.). Proc. Herbaceous Plant Sym. Perennial Plant Assn., Columbus, Ohio.
2. Dejardins, R.L. and Calvin Chong. 1980. Unheated envi- ronments for the overwintering of nursery plants in containers. Can. J. Plant Sci. 60:895-902.
3. Gouin, F.R. 1980. Overwintering container-grown ornamen- tals under thermo-blankets with and without clear, white, or black polyethylene. HortScience 15:491-492.
4. . 1983. Utilizing thermo-blankets in overwinter- irg. p. 53-55. In: Elton M. Smith (ed.). Proc. Herbaceous Plant Symp. Perennial Plant Assn., Columbus, Ohio.
5. Gouin, F.R. and C.B. Link. 1979. Temperature measurement, survival, and growth of container-grown ornamentals, overwintered unprotected, in nursery shelters and under microfoam thremo-blankets. J. Amer. Soc.Hort. Sci. 104:655-658.
6. Hamilton, David F. 1982. Procedures and structures for overwintering nursery stock. Amer. Nurseryman 156(9):97- 98.
7. Hamrick, Debbie. 1985. Overwintering perennials. Grower Talks 49(8):130, 132-134.
Hemming, E. Sam. 1981. This business of ours. Amer. Nurseryman 152(11):37-38.
9. Hickleton, Peter R. 1982. Effectiveness of 4 coverings for overwintering container grown ornamentals in different plant hardiness zones. HortScience 17:205-207.
10. McNiel, Robert E. and George A. Duncan. 1983. Foam tops poly for overwintering container stock. Amer. Nurseryman 158(11):94-101.
11. Patch, F. Wallace. 1983. Growers cover their plants to get through winter. Amer. Nurserman 157(1):113-117.
21 22
12. Perry, Leonard P. 1985. Overwintering herbaceous peren- nials. p. 80-83. In: Steven M. Still (ed.). Proc. Herba- ceous Perennial Plant Symp. Perennial Plant Assn., Columbus, Ohio.
13. Smith, Elton M. 1979. Prevent winter damage by helping plants become acclimated. Amer. Nurseryman 150(4):11.
14. Swanson, Bert T. 1981. Effective methods for protecting nursery stock in winter. Amer. Nurseryman 154(7):9,56-60.