Patrick N. McGovern 2023
The Active Shoot Propagation (ASP) process involves establishing freshly cut, actively growing softwood poplar shoots in a high humidity indoor environment using Hykolity LED 5000K daylight shop lights to encourage root production. Depending on the stock genetics and health, root initiation of rootable materials can occur within several days and entire propagation iterations of good rooting materials can be completed within 10 to 15 days.
The "Winter ASP" (WASP) process typically begins by flushing shoots from 15 cm dormant hardwood cuttings collected during early Spring under 18 cm high humidity domes and LED shop lights with similar requirements used for producing "Aspen Seed Propagation Under Fluorescent Lights" [2]. Then the rooted WASP plants or actively growing shoots (ASP) are cut and propagated to produce growing stock for another iteration of shoots or transplanted outdoors. Propagation via actively growing shoots has also been used for aspen [1] and grape [3] species.
The Seedling ASP process (SASP) applies the ASP process to seedlings in the nursery then selecting ortets and ramets with high ASP rooting potential. The speculation is that rooting performance of some actively growing shoots may be genetically controlled and may correlate to both ASP and dormant hardwood cutting root rates. This process may expedite the nursery ramp-up phase by making good rooting selections in the first year of the seedling. The process entails planting seedlings in the nursery then harvest the three leaf tips via the ASP process when the stock is about 25 cm tall. The remaining seedlings will recover and can be used for other purposes such as comparing the seedlings in the following year for ASP and dormant cutting rooting rates.
Materials and Methods
Materials:
Soil Media: Mix medium textured perlite (~2 mm diameter) with Epsoma Organic seed starter media at a 1:1 ratio in a clean container and a well ventilated area using a face mask. This media is referred to as "EP" Obtain washed play sand to be used as a 1 cm topping after cuttings are planted, which is referred to as "EPS" media.
Greenhouse Domes: Use clear 18 cm "tall" humidity "greenhouse domes". Set the top vents to 25% open during the first week then gradually open them 100% open after 2 weeks. Humidify the flat with a spray bottle daily for the first 2 weeks. Remove the domes after about 27 days when good rooting clones should have sufficient roots.
Containers: Use full flats with the green house domes available at garden centers to increase humidity, promote growth. Start 15 cm WASP cuttings with 7 cm x 7 cm x 6 cm deep trays and conventional 72 hole trays may be used to propagate individual ASP harvested shoots.
Fertilizer Solution Rates:
Light Solution (1/4 rate): Mix 1/4 tsp of 20:20:20 water soluble fertilizer (eg. Miracle Grow) with 1 gallon of water.
Strong Solution (1 tsp rate): Mix .5 tsp of 20:20:20 water soluble fertilizer (eg. Miracle Grow) with 1 gallon of water.
LED Shop Lighting: Hang 3 sets of double 1.2 meter hykolity linkable 42 Watt, 5000K Daylight LED lights 18 cm over a level bench. Light sets should be spaced evenly apart to cover three or four flats width-wise. Use a 24 hour timer adjusted to allow 8 hours of darkness.
Heating/Cooling: Try to maintain an internal dome temperatures range of 21 C to 27 C. Simple meat thermometers can be placed inside the domes to monitor temperatures. Use a 1.2 meter heating pad to increase temperature, and drape a white plastic table cloth over the lights to trap additional heat from the LED lights. Use a fan over the lighting area to help decrease temperatures. Set the darkness during the heat of the day to also reduce temperatures.
Moisture Maintenance: Use a hand spray bottle to mist inside dome several times a day for the first week, then check media moisture every ~4 days with a moisture test gauge and bamboo skewers. Let moisture level go down to .5 then add water to flat bottom to re-hydrate trays.
Miscellaneous Items: 1 qt adjustable spray bottle with clean water. A small thermometer. A clean, razor sharp cutting tool. A small pen-sized screw driver to create stem holes in the media.
WASP cuttings: Harvest whips having vigorous current year growth. Make 15 cm cuttings, ideally with about 10 mm diameter. Bundle, label and store cuttings in freezer ziploc bags at -1 C.
Media Preparation and planting WASP/ASP cuttings: Fill the 7 cm planting trays with the EP media to about 13 cm from the top, then add a 1 cm layer of sand. Carefully immerse the tray into the applicable fertilizer solution (1 tsp rate for WASP cuttings and 1/4 tsp rate for ASP shoots) to completely soak the entire tray. Then insert the WASP or ASP cuttings and re-immerse the trays into the fertilizer solution to level and set the sand layer. Avoid re-soaking the trays with fertilizer after the initial application.
Harvest ASP shoots: The ideal ASP shoot will include the meristematic tip and have 5-7 leaves with the largest leaf being ~40 mm wide. Place shoots in water until planting. Note that the WASP process is designed to force shoots at the expense of rooting, since some clones root poorly anyway. Cut ASP shoots after about 16 days with poor rooting clones to avoid shoot failure for WASP cuttings with no roots.
ASP Shoot Tips: Cut softwood cuttings with a clean, razor sharp tool from healthy, actively growing indoor grown shoot tips of the target plant and plant immediately (transport in water as needed) into the soil media. The stem should feel soft and pliable as lignified stems may not root. The speculation is that fluorescent lights and high humidity may promote less lignification. Shoot tips harvested from a greenhouse or outdoor conditions will need to be cut back and re-established indoors as "mother plants", since they may need to re-adjust to the indoor conditions. The resulting new shoots can then be used in ASP tests.
Planting Shoot Tips: Optionally, use a small tool (e.g. bamboo skewer) to poke planting holes in the media. Hold the largest lower leaves of the shoot tip using your thumb and index finger and place the stem into the hole with part of the lowest leaf. Spray enough water onto the sand to fill in the planting hole and cover the lower stem/leaf with sand. This will effectively lock the ASP cutting into place.
Rooting Initiation Period: Place the planted trays in the flat, cover with the plastic dome and put under the lights. Install a small thermometer into each flat and try to maintain internal dome temperatures of about 21 C to 27 C. Root initiation of "rootable" materials can occur within a 3 to 10 days but selection of good rooting clones should take place at around 27 days. Removing the dome will generally kill plants that do not have sufficient roots. Rooting can be checked by gently tugging the shoots to feel if they are rooted. Likewise, the shoot leaves and appical growing tip should be healthy and appear actively growing.
ASP shoot maturation period: Ideally, ASP shoots should be established after about 22 days. At this time, additional ASP cuttings can be harvested and replanted from the established shoots or hardened off to transplant outdoors.
ASP Iteration Labeling: It may be possible to continue iterations of ASP shoot propagation as long as the parent shoot remains healthy, green and not too lignified. Label iterations with related numerical suffixes using the syntax YearTestLetter.IterationNbr (e.g. 22D.1 (Year 2022, Test"D",Iteration1), 22D.1.1, 22D1.1.2, etc)
Transplant Preparation: Growing aspens under fluorescent lights may produce less lignified shoots compared to greenhouse grown stock. The material can be "hardened" by cutting the stems to about 5 cm height, leaving several leaves to re-generate new growth from the residual leaf buds. It may also help to direct a light fan across the plants during the light period to emulate outdoor conditions. Be sure to watch soil moisture during this time. The stock should be ready for outdoor transplanting after growing about 2" of new growth. Then prop open the dome 4 cm for at about 5 days to wean off the plants, then wean off again under outdoor shade before nursery planting.
Potential WASP/ASP Schedule (Grand Rapids, MI):
3/1: Harvest/process/refrigerate stool whips via 15cm WASP cuttings
3/1: Plant 15cm WASP cuttings under LED shop lights, 18 cm domes (grow 16 days)
3/17: Harvest and start ASP shoots (grow 22 days)
April 8: Wean ASP shoots 5 days. Optionally, harvest some shoots for another ASP iteration.
April 13: Wean outdoors under a light porch shade for 4 days,
April 16: plant in nursery
We have observed that root and shoot growth tends to improve for the same clones as the season progresses towards natural bud break. Therefore it is important to develop control clones, relative scoring methods and compare the results across multiple years for the same or similar treatments.
A listing of links to some WASP propagation photos:
2024: 24D-WASP-ASP Propagation
2024: 24C-WASP Propagation
1. HANSEN, E. A., H. M. PHIPPS and D. N. TOLSTED (1979): Rooting greenwood tip cuttings of a difficult-to-root Populus clone. Tree Plant. Not. 30: 9-11.
2. McGovern, Patrick (2012) Aspen Seed Propagation Under Fluorescent Lights. Retrieved from https://sites.google.com/site/open4st/faq/aspen-seed-propagation-under-fluorescent-lights
3. Walker A.M., Golino D. A. (1999) Rapid Propagation of Grape Planting Stock. Practical Winery & Vineyard. Retrieved from http://www.practicalwinery.com/mayjune99/rapidpropagation.htm