TBD - Update for 2025
A five year Open4st nursery culture and selection strategy is described that may accelerate selection times by planting a family field trial and nursery clonal tests simultaneously. It involves planting 8" cuttings in nursery trials that select clones for rooting from dormant cuttings with high survival rates and stem vigor. The combined nursery and field trial data can be summarized to assist with the clonal selection process.
Introduction
A nursery culture and selection strategy for low-resource applications involves planting 8" cuttings in nursery trials that select clones for rooting from dormant cuttings with high survival rates and stem vigor. The "Vigor Survival" metric is used as a scoring method to describe this pattern. It is derived by multiplying the dormant cutting survival rate by the median collar diameter (mm) in a replicated clone set. Over time, the separate family field trial selections may leverage good rooting clones and historical metrics from the nursery trials with a combined rooting and field performance context. This nursery rooted cutting selection process is based on the Canadian P. alba propagation and selection model as described by Heimburer [1].
Nusery Site Requirements:
A level, fertile and well drained sandy loam soil.
Wind protection and fencing to protect from animals. Rabbit protection may require poultry fencing along the entire perimeter.
An irrigation system that can be activated in the morning to avoid disease issues.
A disease and insect strategy that works for your area and species.
Nursery tools: Shovel, Custom T bar tree lifting spade recommended design by Mike Morin (Hramor Nursery). Steel spade dimensions: 44” long, 13” bar, 10.5” long x 9” wide x ¼” thick blade with a one inch tapered edge, A garden fork. Craftsman 10" band saw to cut whips into cuttings Prepare initial nursery with a rear tine tiller, then use a garden fork to loosen soil for later iterations.
Dormant Cutting Preparation:
Lifting the stock: Open4st typically lifts nursery stock in early Spring using the custom T bar lifting spade with the edge sharpened with a file to ease lifting. The spade is used to make a single line trench straight down and 4" from the stems. Then on the other side of the row another cut is made 6" from the stems but at a 45 degree angle down. The idea is to cut through the roots then push down on the spade to lift up the trees, listening and feeling for the trees to loosen from the earth. Trees with a strong taproot may require deeper cuts and multiple lifts. Trees that are not completely severed may have some roots tear from the cutting stem, which is usually cosmetic if there are enough residual roots. Once severed the entire row of trees can be lifted by hand along with the associated tree labels. See: Custom T bar tree lifting spade and nursery photos.
Sorting and Heeling the stock: The trees are sorted on a table, roots pruned and the stock is counted, recorded and bundled with 2 plastic coated wire ties with plastic casing. The bundled stock can be bagged and placed in cold storage (longer term) or heeled in labeled groups of upright bundles (shorter term) with trenches back filled to remove air gaps. When done, drench the material with a soaker spray of water and stake the rows with the variety label. The upright storage allows easier stock identification and retrieval.
Spring Cutting preparation and storage: Open4st cutting preparation typically begins in March with lifting, washing the stock with a hose and allowing them to dry enough to prevent handling and refrigerating wet stock. Then use a 10" band saw to make cuttings to the desired length. Typically 8" cuttings are used for the nursery and 10" or 14" cuttings for field planting depending on the site. Nursery cuttings shorter than 8" may rock back and forth in the wind and lean over if they are over 6' tall. Also, 8" cuttings are closer to the 10" field grade standard length and provide a more realistic selection length for nursery cutting survival rates. Cutting sets are grouped with 1 or 2 rubber bands and 10" x 3/4" plastic labels (RapiClip Brand) with the variety name marked with a heavy duty construction grade pencil. Cuttings are stored in a 1 gallon freezer bag in a refrigerator at 30 degrees Fahrenheit.
Nursery Preparation and Planting:
The Open4st nursery uses a rear tined roto-tiller when soil is dry in early Spring, incorporating organic matter from the previous season (grass clippings and leaves). Another option is to simply areate existing rows from the previous year with a garden fork.
Open4st nursery applies fertilizer and soil amendments per soil test results, typically from May 15 to July 15. While the control clone DN34 stops growing in August, hybrid aspens may continue to grow in September so it is important to avoid late fertilizer applications that may impact the hardening off process.
Test the planting rows by inserting 8" cuttings that should easily penetrate to a 7" depth. Use a garden fork to loosen the soil if there is significant resistance. Draw a staked string over the first row in a direction allowing drainage off-site from heavy rain. Use a metal rake to create a raised row centered under the string then level the row to about 3" to 4" deep and 10" wide.
Planting the previous year's stock (dormant cuttings and bare root) typically begins the first week in April. Seedlings are usually planted around the first of June or July depending on seedling availability.
Ideally, dormant cuttings should be pre-soaked in a bucket of water for about 24 hours prior to planting.
All Open4st seedlings, cuttings and mini-stools are planted in double rows typically on 36" centers.
An 8' 2 x 4 board is marked with the plant distances and centered below the row string. The plastic label is placed at the start of each row and larger wooden stakes denoting replication sections that have the same treatments with the same stock type, size, count but different varieties. The 8" cuttings are planted next to the board marks, 7" inches deep with the buds pointed up.
After a row of dormant cuttings is planted it should be gently watered with a garden hose "shower" attachment. Then the 4" middle area between the cutting double rows should be "capped" with a 3" deep weed free mulch applied to reduce moisture loss, weed issues and maintain a favorable plant rooting environment. Open4st uses MiracleGro's Spagnum Peat Moss or Sta-Green Peat Moss products that don't repel water like typical peat moss.
Greenhouse grown aspen seedlings (e.g. via Rakers Greenhouse) may have a 6 or 7 week growing period and attain 3" to 6" tall depending on species and growing period. Greenouse seedling leaves are tender and can be damaged with the peat moss covering or scorched by heat and sunlight. Consider hardening off the seedlings by setting the flats in the light shade of a protected porch or tree for 3 days before transplanting. Be careful to check the flat for dry cells and gently soak as needed. Prepare the seedbed by first watering the soil, plant the seedlings, apply the dry peat moss then carefully deep soak the peat moss.
These materials will have little or no roots for a period of time and will require careful monitoring for dryness directly at the cutting or seedling zones. A watering can or a 5 gallon bucket with a 1/2 hole can be used put water directly in the critical areas without damaging leaves or causing excess erosion.
The area between the double rows is typically hoed occasionally then covered with composted grass clippings or chopped leaves to reduce weed growth.
After planting record the relevant details in the test_detail table (see: Using and accessing the r4st database and Open4st Database Column and Naming Descriptions). The initial details will include: variety name (test_detail_key), notes, stock type, stock length, stock diameter, start quantity, this_start_date, row, column and replication number that will have the same treatments with the same stock type, size, count but different varieties.
Four Year Testing and Ramp Up to Clonal Trial Material:
Year 1 - Produce and Grow Seedlings: Produce aspen seed from controlled crosses, grow them in a greenhouse, or indoors under fluorescent lights. Store excess seed in labeled paper coin envelopes over calcium chloride desiccant and put in a freezer. Out-plant the seedlings when they are 3-5" tall in dual rows 4" apart with rows centered 3 feet apart and seedlings 4" apart to grow them 4' - 5' tall. Record the relevant seedling nursery details in the test_detail table using the "SEL" stock_type. See: Using and accessing the r4st database.
Year 1 Winter: Conduct WASP 4" tip rooting tests on tip samples from each family to estimate family rooting potential. Also sample some larger whip stems to observe family percentages for having Figured Wood (FW). Use this data to estimate rooting and FW potential at the family level and determine how many ortets to propagate for each family in year 2. Map the WASP tips back to the 1-0 seedlings if a family field trial is planned. The WASP indoor process can be leveraged during late Winter using small diameter stems to ramp up high value selections as needed.
Year 2 - Plant a Family Field Trial
A family field trial should have the highest resource priority. It may be possible to identify promising families at age 5-6 then recreate those families to produce larger populations for more selection opportunities. A scenario could involve planting 32 seedlings per family in four blocks each having two four tree linear or square tree plots.
If resources allow, consider including the best rooting WASP selections with the 1-0 ortet seedlings and for nursery testing.
Year 2 - Nursery First Year Ramp-up:
Depending on nursery space resources, select a set of the largest ortet seedlings from each family and plant 4-6 - 8" cuttings per ortet on 4" spacings since the survival rate is likely unknown and to establish some vigor survival metrics. Plant standardized cutting diameters for consistency (eg. 7mm to 12mm), which may not be possible if the stock is only 3' tall. This will test for good rooting clones via 8" cuttings. Try to keep consistent quantities per replication set for easier record keeping and accuracy.
In the Fall: Record the relevant cutting (DC) details in the test_detail table. The post season details will include: notes, end_quantity (living, plantable rooted trees over 1' tall). Then find the median sized tree in the set and measure the collar in millimeters and record it in one of 3 applicable columns: "collar_median_dia_mm" for rooted cuttings, "collar_1_1_median_dia" for 1-1 stock and stool_collar_median_mm for Mini-Stool stock. The "is_plus_ynu" column is intended for as a Yes, No or Unknown subjective observation of a few really good or really bad individuals. It provides a human observation in the context where the variety was grown. Record the sum total of a varieties field grade cuttings in feet in the "field_cuttings_ft" column then any "leaf_score" values if applicable.
The median and survival rate data are used to make "vigor_survival" metrics that will be helpful to make nursery performance selections.
In the following Spring: When making cuttings, test the bottom cutting for for signs of figured wood by inspecting for banded patterns in the split sections.
Year 3 - Second Ramp-up & Selection:
Select a set of the selected clonal ramets that can be consistently retested with available resources. Discard other clones that don't meet the minimal propagation, disease or other trait criteria. Open4st typically retests 8 cuttings of selected clones on 6" dual row spacings (four trees per foot).
Use vigor/survival metrics to make selections in the Fall. Discard other clones that don't meet the minimal propagation, disease or other trait criteria.
Year 4 - Third Ramp-up and re-test:
There should now be adequate material per clone to distribute to cooperators, but testing one more year in the nursery is recommended to verify rooting performance over 3 years.
Plant several nursery replications of 10 or more 8" cuttings with standardized cutting diameters (eg. 7mm to 12mm).
Measure field trial DBH and heights and compare family rankings to nursery selections at family level.
Year 5 - Release materials for additional clonal trials:
Release to cooperators
Results
The annual nursery results for survival rate, leaf issues and growth can be summarized and compared to the field trial data to assist with the clonal selection process (see vw_2023_5_nursery_field_summary). Accelerated selection may result when nursery and family field trials commence at the same time allowing the near term nursery trials to identify exceptional clones (e.g. good rooting or high figure) that can compliment the longer term results of the field trials.
1. Heimburger, C. (1968) Poplar breeding in Canada. p.88-100. In Growth and utilization of poplars in Canada, J.S. Maini and J.H. Cayford, editors. Canada, Department of Forestry and Rural Development, Forestry Branch, Departmental Publication 1205, 257p. Ottawa, Ontario.