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Root Production Method: RPM, do you know it?

Austin Verde

Joined: Apr 13, 2012
Posts: 13
So, basically from what I can surmise: RPM involves raising trees in containers that allow for air pruning of roots. When the roots come into contact with the air, they stop growing/die back and this encourages new root growth.

Check it out here: http://www.fs.fed.us/rm/pubs/rmrs_p024/rmrs_p024_020_021.pdf

It seems like they just use pots that dont have bottoms and are shallower & wider than normal. This nursery: www.fknursery.com raises seedling trees using RPM here in MO.

I guess I'm curious to learn more about the air pruning technique. Does anyone have any knowledge on the subject? There are a lot of products out there that claim to air prune such as at http://www.rootmaker.com. But it seems that at forrest Keeling nursery and in the RPM pdf that the bottoms are just cut off of regular pots.

I'm interested in this because I order hundreds of seedling trees every spring and their bare-root systems are as sad as can be. Over the past few years I've had barely a 60% survival rate and those that do survive grow slowly. I'd love to be able to spend a year nursing these seedlings into having vigorous developed root systems before planting and then not loosing so many trees.

So far all Ive figured out is
step 1: put seedlings in pot without a bottom
step 2: put seedling in bigger pot without a bottom.

There's got to be more to it than this.

Joined: Jan 13, 2010
Posts: 238
Location: swampland virginia
soil blocks make the same claim for seedlings. there maybe some info they have to help you on the air pruning.

since you were interested in trees, posted the following on page 2 of the forum thread http://www.permies.com/forums/posts/list/40/998. it might help you with some of them surviving better.
Dr Temp wrote:Some trees respond to planting them deep like a tomato transplant. Others do not like it and take to an early grave. Not sure what the apple tree sapling thinks. Here's a video clip. The fun starts at minute 6.
or read the transcript starting with 'LONG-STEM PLANTING'.

aspirin or willow bark may help them generate some new roots a little better.
one of the forums here mentioned digging another hole next to them and putting wood chips in it for the roots to grow into and get minerals / water.
old saying on spend more money on the hole then the plant.

the seedlings i have ordered have had similar issues. some make it, some do not. I think there are a lot of shocks going on with the plants being packed, shipped, unpacked, and set in yet another new environment. guess there are not enough local propagators of good quality plants and varieties.
Ray South

Joined: Jul 11, 2011
Posts: 46
Location: Northern Tablelands, NSW, Australia
I work from time to time in a community owned nursery that produces about 30,000 trees a year, give or take. All such stock is grown in 40 cell Hiko trays, effectively small tubes with no bottom. The maximum time in one of these trays is two years. After that, the plant becomes too difficult to care for as there is just solid root in the tube. These are thrown away as they never seem to do well when planted out. Best planting is when the plants are 12 to 18 months old. Quite often, for retail stock, some are potted on into forest tubes. These are larger and longer than Hiko tubes. They have very open bottom ends. These are grown on for a number of months so that the root mass fills the pot. All stock, whether it be Hiko or forest tube is kept on mesh racks off the ground so that the roots air-prune. This happens without any intervention.
We also do a lot of planting and have been experimenting with long-stem planting. Basically, we ensure the plants are well fed so that the tops are tall relative to the pot length. We dig quite a deep hole, fill with water and drop the plant in so that only about 10cm pokes out. Back fill, water again and that's it. This works extremely well, especially if you are unable to get back to the plant for follow-up watering. The seedlings grow roots from the stem that is buried too. This has been done successfully with Eucalyptus, Callistemon, Acacia, Melaleuca, Casuarina and a good number of other genera.
Hope this helps.
osker brown

Joined: Jun 28, 2011
Posts: 146
Location: Southern Appalachia
There is a permaculture nursery in my area (Useful Plants Nursery), that puts some of their larger trees in "RootTrapper" fabric pots (the same ones you linked to). I have an Illinois Everbearing mulberry in one that I haven't planted yet, so I'm not sure how the roots look in them. They also use the smaller airpruning plastic seedling pots from that company. I haven't handled their plants enough to say for certain how well they work, but the guy who runs the nursery has been in the horticulture business for 35 years, and I've seen their nursery.

I have used airpruning fabric pots quite a lot with containerized annuals. I sewed up my own version of Smartpots using landscape fabric, which took a decent amount of time but cost very little. The advantage with that over just bottomless pots is that the lateral roots also get pruned, so once you transplant you have a solid root ball surrounded by loose soil, rather than a root mass on the sides with mostly loose soil in the middle. I've also cut out the bottoms of all my seedling pots for the past 2-3 years and it seems to cut down on transplant shock with veggies.

Also worth mentioning is my potting mix. I don't have exact percentages, but it's about 1/3 biochar 1/3 rotten wood chips 1/3 compost. The biochar holds lots of air pockets, the wood holds lots of water. The mix is quite a bit heavier when wet than the potting mix you buy at the store, but I find that the added aeration from the fabric and bottomless pots compensates.

I'm going to be experimenting with this a lot this year so I'll update as I start playing with more tree/shrub seeds.


Glorious Forest Farm
subject: Root Production Method: RPM, do you know it?