ESRM 412 – Native Plant Production
Spring 2005 – Prof.
Guidebook for Native Plant Propagation:
Development and construction of an air-pruning propagation bench, and its proper use
Why use such a system?
An air-pruning propagation system is a low-cost, efficient method of propagating cuttings, seedlings or container plants for restoration projects. Air pruning happens naturally when roots are exposed to air in the absence of high humidity. The roots are effectively “burned” off, causing the plant to constantly produce new and healthy branching roots. If roots are not exposed to air, they continue to grow around the container in a constricted pattern. The roots may spiral, twist, kink or become strangled. When the plant is later installed it will likely fail to establish a normal root structure, and instead will have reduced uptake of water and nutrients. Eventually abnormal growth should be obvious and could cause the plant to fail. Damaged root systems also cause leaves to turn yellow or brown, shrivel or drop. Healthy, highly branched root structures allow a plant to more efficiently uptake water and nutrients while increasing growth and overall plant health. A strong root system will make a plant better able to establish itself when installed in a restoration project.
Strangled Twist Crank handle
Pot-bound Spiral Well developed
[i]Comparison of poor root structures to a well developed root structure
[iii]Example of air-pruning using commercially available plug trays
Advantages of air-pruning:
· promotes branched root systems
· encourages new roots to sprout
· prevents roots from spiraling
· prevents plants from becoming pot-bound
· plants may remain in pots, plugs or plant bands longer
[iv]Branched root structures resulting from air-pruning methods
[v]Healthy air pruned roots at open base of cell
How do you most effectively utilize an air-pruning bench?
Depending on the climate and plant material the benches may be set up outside, in a hoop house or greenhouse. In an enclosed structure more careful monitoring of humidity and air flow is necessary.
Watering should be done from above either manually, with a drip irrigation system or a mist system. When propagating cuttings or seedlings a mist irrigation system may be the best option. The misting system can be constructed using irrigation supplies from your local hardware store or kits are available from many online retailers.
[vi]Plant bands: note the side holes for promoting lateral root pruning
Seeds or cuttings should be propagated in plugs or plant bands. Plant bands are open-bottomed paper sleeves and are highly recommended (see www.hummert.com). Roots easily air-prune below and the paper will decompose when planted. Plugs may be less effective, needing lots of openings for air to hit the roots, including side slits. Any side air contact in either the plant bands or plugs will help to prune the lateral roots. It also can be difficult to remove plant material from plug trays.
[vii]Air-pruning plug tray with open bottom and mesh base
When using plant bands it is vital to remember to carefully monitor moisture levels as the paper sleeves can wick water away from the plant.
It is important to use a soil mixture that has a high water holding capacity to accommodate the extensive root structure development and tendency of plant bands to dry out. Drainage should not be an issue as the bench is suspended off the ground.
Air-pruning is also highly effective for propagating trees. It increases the “shelf-life” of the plant material, prevents root circling, and increases the success of plant installations because the transplants establish quickly. Using such systems eliminates the need to re-pot as the tree grows, as small plants can be potted directly into large containers. This type of pot causes the plant to develop a dense root ball of tiny white roots filled with carbohydrates, ready to branch out when planted. The root ball may also be more resistant to extreme temperatures. This can greatly increase the survival rate of plant material installed in a restoration project.
[viii]Air-pruning pots are used to eliminate root circling in tree production
This shows eucalyptus root development using an air-pruning pot
How do you know the roots are air-pruning properly?
No roots should be visible outside or beneath the container. If you can see small white tips of roots try:
· increasing the air flow with fans
· raising up the bench
· decreasing the humidity (increase ventilation)
The propagation bench:
Many different designs would be effective. The basic needs are an open metal surface raised up off the ground, such as a mesh, that allows air to flow freely. It should be at least 16-24” high to allow air to circulate beneath. Standard height for a typical (non-air-pruning) propagation bench is 36”. This height accommodates someone in a wheelchair to get up close to the plants. The frame can be constructed out of treated lumber, metal, concrete or plastic. While concrete makes a very sturdy table that can support great amounts of weight, it is a much more permanent type of construction than the other options.
[ix]Metal benches such as this are highly effective, and are readily available online
To build a relatively inexpensive and sturdy bench you’ll need to construct a wooden frame and create a surface of wire mesh. The precise dimensions of each table should vary according to your particular needs. In this example the base of the bench is made of two 16” cinder blocks and a 16” piece of the 1-inch by 4-inch treated lumber.
· Lay the bottom cinder block horizontally on the floor.
· Set the second cinder block vertically centered on the bottom block
· Lay the 16” piece of lumber flat across the upper block
· rest the frame on these legs, placed 4’ on center along the edges of the bench
The frame should be 4 feet deep, and may be as long as needed for the space. 2-inch by 4-inch treated lumber should be used to construct a simple frame to which the mesh metal surface is attached.
The height of the bench can be raised by adding additional horizontal cinder blocks. This design will yield a bench the recommended height of at least 16-24”.
[xi]This shows a similar bench. Here the legs have been placed at the corners.
[i] Image source : http://www.nda.agric.za/docs/macadamia/macadamia.htm
[ii] Image source : http://www.rhs.org.uk/advice/profiles0404/plant_establishment.asp
[iii] Image source : http://www.renaldo.org/renaldosales/ag/airprune.html
[iv] Image source : http://www.renaldo.org/renaldosales/ag/airprune.html
[v] Image source : http://www.sierrahort.com/conifer.htm
[vi] Image source : http://www.hummert.com/catalog.asp?P=2748
[vii] Image source : http://www.renaldo.org/renaldosales/ag/airprune.html
[ix] Image source : http://www.alumni.ca/~rich4k0/images/greenhouse_bench.jpg
[x] The instructions for building this bench were found on the West Virginia University Extension Service website : http://www.wvu.edu/~agexten/hortcult/greenhou/grencons.htm
[xi] Image source : http://www.ashland-city.k12.oh.us/ahs/classes/hort/2003/feb26/move2.jpg