April Apple Grafting and Air Prune Box Update

 Apple Grafting Update

On 4/16/2025, it was noted that these grafted plants had had too much time inside (see Figures 1-3).  Too many growing degree days accumulated too quickly in the interior basement room of my house, and they broke from dormancy earlier than desired, as it was still too cold to move them fully outside into the air prune box.  Plants were moved in an unheated farmhouse garage while construction of the air prune bed was finished.

As can be seen in Figures 1-3, Hudson's, William's Pride (WP) and Pristine all took off at the top (from the scion) quickly. By April 25th, almost all of the grafts had green leaves above the graft union, as is shown in Figure 4.  Figure 4 also shows that many had leaves below the graft union that needed to be removed. Whenever this happened, the buds were stripped immediately.  On 4/25/25, all grafts were moved into the air prune box per Figure 5.

Figure 1. Pristine (L) and Hubbardston Nonsuch (R) on 4/16/25.

Figure 2.William's Pride (L), Freedom (R, bottom), and Gilpin (R, top) on 4/16/25.

Figure 3. Hudson's Golden Gem (L) and Pink Pearl (R) on 4/16/25.

Figure 4. Green growth took off on the apples between April 16th and 25th.  Again, all shoots below the graft union were pinched off.  All flower buds were pinched off when spotted.

Figure 5. Plants placed in the air prune box on 4/25/2025.

Small Nut Tree Update

Figures 6 & 7 show that several nut trees were also moved from small start containers into the air prune box.  While most showed a nice taproot, there was 1 oak tree that had a "confused" tap root, as is shown in Figure 7.

Figure 6. Several swamp oaks and northern pecans were planted from seed taken from the 2024 MNFGA meetings.

Figure 7. Tap root comparisons.

Air Prune Box Construction

Two air prune beds were constructed between 4/16/2025 and 4/18/2025 using a pocket hole jig, treated 2x4 lumber, and untreated cedar for everything else (per the plans published earlier).  Figures 8-13 show the air prune box assembly process.

First, all wood was cut or ripped to the appropriate dimensions.  Pocket holes were drilled in the shorter pieces and would face the exterior of the box when possible (Figures 8 and 9).  If the fit of the boards looked good, boards were assembled vertically so that pocket hole screws could be inserted downwards into the wood (shown in Figure 10 with the treated 2x4s).  Figures 11-13 show the addition of the wire mesh on the bottom.  For each box, a slightly different support method was used.  In the first one, a full layer of larger gauge wire with bigger holes was added to help the 1/4" hardware cloth take the weight of the soil (Figure 12).  After stapling the wire mesh in place, the 2x2s were screwed onto it to increase the holding power of the wire mesh.  Figure 13 shows the second method that was used, where 2 lengths of the the larger gauge wire (cut off from the larger pore mesh used in Figure 12) were run the length of the box.  The 1/4" hardware cloth was stapled on top of this and then the 2x2s were again screwed onto the 1/4" hardware cloth to further hold it in place.  Figure 14 shows the fully assembled finished products.  Note that the 2x2 side of the bottom treated lumber piece faces up with the 2x4s on the bottom.  Cement blocks were added to decrease the likelihood of root escape into the native soil.

Figure 8. Purchased boards were cut to length and pocket holes were added as appropriate.  A dedicated plug-in drill was useful for the repeated pocket hole drilling.

Figure 9. Pocket hole screws and assembly table used for checking board lengths and layout.

Figure 10. Boards were placed vertically so that screws could be inserted in a downward direction during assembly.

Figure 11. Materials used to secure the wire mesh bottom of the air prune beds between the 2x4s and 2x2s.

Figure 12. One box had a full extra layer of larger gauge wire below the 1/4" hardware cloth to help support the weight of the soil.

Figure 13. The other box only had two lines of larger gauge wire added to support the 1/4" hardware cloth.

Figure 14. Finished, assembled boxes after soil but before plants.

Air Pruning Box Plans

 Sketchup Pruning Box Plans

These plans are based on the air prune box plans shared by Edible Acres on Youtube.  This design differs from theirs in 3 major ways:

1. These boxes are slightly longer 4' 2 1/2" rather than 4' to minimize wasted wood.  They are also slightly deeper.
2. The center support of the bottom layer of these boxes runs front-to-back down the middle, rather than side to side.  Also, we have 2x4s (rather than 2x2s) supporting the bottom layer for added strength.  We will add an additional layer of remesh or wire underneath the 1/4" hardware cloth to add extra support for all the weight of the soil and trees.
3. Edible Acres used black locust wood, which we do not have.  Instead, we made the bottom layer ground contact treated lumber (and we will report back if this has a notable adverse effect on the trees).  One layer will be 2x6 cedar and another will be 2x8 untreated whitewood/pine.  We will monitor how these hold up over the years.

Figure 1. Air pruning box with dimensions and wood selection

Figure 2. Side view with dimensions

Figure 3. Top View, metal mesh shown will be 1/4" hardware cloth

To make 2 2'x4' 2 1/2" air pruning beds, you will need the following materials:

• 2 12'x2x8 untreated pine boards
• 2 12'x2x6 cedar boards
• 2 12'x2x4 ground contact treated lumber
• 2 8'x2'4 ground contact treated lumber
• 2 13' sections of 24" wide 1/4" hardware cloth (for sidewalls)
• 2 4' sections of 24" wide 1/4" (for bottom)
• 2 4' long, 2' wide sections of remesh or stronger wire for bottom reinforcement (optional?)
• 2 5' long 3' wide 1/4" hardware cloth (for the tops)
• linseed oil and/or outdoor paint
• 2 1/2" or 3" deck screws
• furring strips or scrap lumber to hold down the wire cages on the top
• 
  

Cut list:

The purchased wood should be cut as is shown in Figure 4.

Figure 4. Cut list for air pruning beds

More pictures to come during assembly.

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.