Air Pruning Bed for Tree Propagation

Project PLANT MI (Propagate Local And Notable Trees in Michigan)

We will create seedling trees with good, local genetics.  To do this, we must establish a means to:

1. collect seeds from local, interesting parent material of species of interest with a common cataloging system for source material.
2. stratify seed to get it ready to germinate.
3. propagate seedlings with good root structure.
4. gather data on seedling progress periodically (yearly?) to keep track of plant progress.

Goal 3, propagation, can be achieved with an air pruning bed which prevents the formation of girdling, circling roots.  While the eventual goal will be to build a large air pruning bed for seed placement (like the one here), at present, the images below will outline an initial, stopgap air pruning bed I built in my compost bin (which was chosen because the 1/4" hardware cloth would prevent seed poaching by wildlife).

Figure 1. a) Empty nut storage bin.  b) Fully enclosed compost bin.

A nut storage bin (shown in Figure 1a) was placed on its side inside my 4x4 compost bin (shown in Figure 1b) to make an air gap for the propagation bed, as is shown in Figure 2.

Figure 2. Placement of bin

The compost bin selected was full of leaf litter from the previous fall.  The space around the bin was filled in with pizza boxes (future composting material), pictured in Figure 3.

Figure 3. Adding "sides" to the air pruning bed.

After adding the sides to the air pruning bed, a layer of leaf litter was added on top of the hardware cloth to prevent the soil from falling through the 1/2" holes (Figure 3).  Then 3 buckets of sandy topsoil, 2 buckets of forest soil, and 2 bags of purchased topsoil were added to fill the space.  Finally, some initial stratified seed was added.  Final images are shown in Figures 4 and 5.  Figure 6 shows the approximate placement of the various seeds that were added.

Figure 4. Final Top Down Image of the Air Pruning Bed inside the 1/4" hardware cloth barrier.

Figure 5. Final Top Down Image of the Air Pruning Bed outside the 1/4" hardware cloth barrier.

Figure 6. Arrangement of Stratified Seeds in Air Pruning Bed.

All seeds came from the Fall 2024 MNFGA meeting.  The seeds from small paw paws were from the wild grown ones provided at the meeting for planting.  The seeds from large paw paws came from paw paws purchased at the meeting.  The chestnuts were freely shared at the meeting for planting (unknown if they were Chinese or European-Japanese).  The Jim Buartnuts were from a member who had harvested them in a previous year and brought them for seed or eating.  These are from Jim Sunnerville's Plainwell Buartnut Tree. 

This stopgap air pruning bed is a trial run for PLANT MI.  For future work, the source, location, and any other pertinent information should be known and recorded for each stratified seed, which will be assigned an ID number based on its source and year of harvest.  Additionally, notes would be taken on the stratification.  Once the seeds sprout, they would be given a new tree-ID number that would follow them as they grow.

Kiwiberry Progress Tracking

 Kiwiberry Post-Planting Maintenance

After planting, the kiwiberries were maintained with regular between row mowing and watering.  The growth progress of the plants was documented with images.  

Figure 1. Planting was accomplished between 7/3/24 and 7/9/24.

Figure 2. Evidence that orchard neighbors were curious about the new kiwiberry planting.

Figure 3. Liquid Fence deer/rabbit scent repellent was applied to the plants to prevent nibbling in the initial days of installation.

Kiwiberry Growth Progress

We will compare the growth progress of the following plants as representative of the majority of that plant type within the vineyard.  All were planted on 7/3, unless noted otherwise. The KX-# is the ID number of the plant and represents its location within the planting, as was shared in the previous post on Installation.

• Ken's Red KA-8 - planted 7/9
• male Clark KB-2
• Geneva 3 KB-5
• Changbai Mountain KB-7
• male Fairchild KC-4
• Hardy Red KC-6
• Anna KC-8 - planted 7/5
• male Optiz KD-2, planted 7/9
• male Meader KD-7 - planted 7/9

Each variety showed different initial characteristics that can be seen, generally, in Figure 4 below.  Note the size and replant stress difference between row KC (left) and row KB (right).  Row KB plants were much smaller at the time of planting and so likely underwent less replant/drought stress.

Figure 4. Rows KB and KC were almost fully planted out on 7/3/24.  Row KB (on the right) is mostly comprised of Geneva 3.  Row KC (on the left) is mostly comprised of Hardy Red.  Note the difference in plant size and replant stress.

Initial plant images were taken on 7/19 (before and after the first pruning to reduce replant stress), 7/23 and 8/2.  These are shown in Figures 5-13 below.  Images are shown from left to right in the following order: 7/19 before pruning, 7/19 after pruning, 7/23, 8/2.

Figure 5. KA-8, Ken's Red.

Figure 6. KB-2, male Clark.

Figure 7. KB-5, Geneva 3.

Figure 8. KB-7, Changbai Mountain

Figure 9. KC-4, male Fairchild.

Figure 10. KC-6, Hardy Red.

The Hardy Red variety (Figure 10) struggled to establish quickly, possibly due to the extensive root reorientation that needed to be accomplished during planting.  Almost all of the hardy red plants needed to have the roots extensively detangled and reoriented to head away from the middle of the plant (or circling the plant) during initial planting.  

Figure 11. KC-8, Anna.

Figure 12. KD-2, male Optiz.

The male Optiz plant died all the way to the ground during the first few weeks.  It did grow back from the ground, but in 2025, it remains to be seen how strong this plant will be going forward.

Figure 13. KD-7, male Meader.

The most vigorous plant in the first 30 days was the Geneva 3 (Figure 7), but the Changbai Mountain and male Clark varieties also showed steady strong growth.  Almost all of the plants had curled leaves for the first 10 days, indicating some level of replant/drought stress.  The curled leaves lasted longest in Ken's Red, Clark, Fairchild, and Anna, but all varieties looked much recovered by August 2.

2024 Kiwiberry Installation 3 - Planting

Kiwiberry Installation - Variety Selection

Kiwiberry varieties were selected in conversation with Danny Hartmann (Hartmann's Plant Company) and Iago Hale (Hale Lab, University of New Hampshire, UNH).  They both strongly recommended Geneva 3 as the likeliest variety for this area.  They also mentioned Hardy Red as a red variety of note.  Also available (and planted for the sake of comparison and testing) were Ken's Red, Cheng Bai Mountain, and Anna (MSU was not chosen for this study because it was not available at the time of original planting).  These were all female plants, and male pollenizers needed to be chosen per the recommendations published by Nor-east Kiwiberries, an excellent and thorough production guide from the Hale lab at UNH that can be found here <https://www.noreastkiwiberries.com/production-guide/>.  We selected Optiz, Fairchild, Meader, and Clark for genetic variety.  The final plant trial layout is shown below.

There are 4 rows (KA-KD) of 9 plants each.  Male varieties are highlighted for reference.  Row KA is the southernmost row, with rows running west to east.  Black lines represent the inline trellis post placement.  Rows will be numbered 1-9 from left to right (west to east).

6 males and 30 females were planted (to maintain the1:6 ratio recommended by UNH for optimal pollen availability).  We tried to randomize the variety placement so that location effect could be minimized.  This UNH thesis suggests the following layout for male and female plants in Figure 19 (Hastings, W., "Growing Kiwiberries in New England: A Guide for Regional Producers", Master's Degree Thesis, University of New Hampshire, 2018).

The planting site is a north-facing slope with the two Anna's in KA at the highest end of the slope and the two Geneva's in KD at the lowest end of the 7-8 ft total elevation change (per county topographic maps, shown with the apple trees that were removed from the site in order to plant the kiwiberries).

A topographic map of the ~100 foot by 40 foot planting site is in the black rectangle.

Modified Hügelkultur Approach

It is worth noting that site preparation after the removal of an orchard normally involves the uprooting of existing trees (physically removing the roots from the ground by pushing the trees over and then burning the roots).  At this site, in order to minimize soil disturbance and add carbon to the soil, we decided to grind the stumps to below ground level.  It should be noted that the stump sites during year one did send up shoots that were continually mowed down with a conventional mower during normal maintenance.  We will record notes about how well this works going forward, especially as regards apple shoot control via mowing.

Hügelkultur is a German practice that involves mounding soil on top of large pieces of wood to support fungal dominance in the soil.  Our approach is modified because instead of mounding soil for a raised bed garden, the existing apple tree roots will die and leave behind woody residue in situ.

2024 Kiwiberry Installation 2

Site Preparation - Stump Grinding

On 5/28/24, I rented the Vermer stump grinder (Stump Grinder Vermeer SC30TX) from https://www.pawpawrentals.com/ to take the remaining apple tree stumps to below ground level to allow for normal mowing in between the rows.  As can be seen in the images below, the weeds got to mid-calf by the time stump grinding was finished.

Site Preparation - Weed Suppression

By 6/19/24, several passes with our John Deere 40 belly mower and followup walking/visual detection helped remove the large remaining wood pieces, allowing the grass to be maintained at a normal lawn height.  The next step was to put down weed suppression mats or row cover.  As can be seen below, we put down some fabric weed mat with cardboard underneath, the rest was accomplished with woven plastic, donated by Danny Hartmann of Hartmann's Plant Company <https://hartmannsplantcompany.com/>.

On 6/28/24 we rented a mini-trencher for burying the edges of the weed suppression mats (also from Paw Paw Rental).  Burying the edges of the weed mat would keep it in place (a la Steven Sobkowiak at Miracle Farms in the film, "The Permaculture Orchard").  

On 7/2 we began planting the kiwiberries into the rows.  This process will be covered in a future post, but for weed suppression, the plastic sheeting was secured by burying one side and staking the other as the plants went in.  It was melted with a soldering iron to go around the posts and over the tops of the plants so that it would not unravel.  In the future, I would recommend trenching after the plastic sheeting is laid out so that appropriate spacing can be maintained between the trenches.  It would also minimize soil exposure to time/rain/sun which can cause the soil used for burying to become hardened.