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.