The RootMaker bags are designed to air prune the root tips. Plants are placed in the bag and inserted into a concrete block cell. The block helps regulate moisture, plant spacing and other benefits. Plant and root growth is accelerated with no circling of roots as can often be found in round, plastic pots.
The year 2000 saw a tremendous growth in our sales of Eucalyptus over the internet. Most of our plants are "shipped out of state" and I quickly realized it was proving extremely difficult to ship large plants. The three gallon pot sizes were bulky, heavy and just boxing them up was a real challenge. The customer pays for the shipping - many times the freight bills exceed the cost of the plants.
The 4" pots we were using proved another challenge. We had to pack paper around the base of the plant and tape it down to the pot - a very time consuming process. Some of our Eucalyptus in the 4" pots were growing quite fast. I felt that a 4" pot size did not contain enough media to support fast growing trees. It appeared to me that many plants were outgrowing the pot size so we started stepping up from a 4" pot to 1 gallon to 3 gallon size.
I discovered a relatively new product on the market where you grow your plant in a mesh bag that is placed in a concrete block cell. (The actual product name is RootMaker knit fabric container) (Cinder-block, concrete block, building block, are all the same thing - just a difference in what name you call it in your area. For the purposes of this article, I will just use the term "block".) By the time I finished reading the article - it really was making good sense and sounded logical. I ordered a few bags to try and decided to test them against our current growing methods using plastic pots, the standard for the nursery trade.
Once the bags arrived I read over the article again and established my test plot. I chose some of the Eucalyptus that were growing in the 4" pots to be the test species. The test would consist of approximate equal size plants - half would be put into the mesh bag, the other half stepped up to one gallon size plastic nursery pots.
The media was mixed using aged pine bark, peat, perlite and vermiculite. Our standard 18-6-12 fertilizer was incorporated well into the mix and we potted up our test plants.
It did not take long for us to see results. Within 2 weeks, the plants in the mesh bags were 1/3 taller than those in the 1 gallon pots. Everything was growing in the same area, received the same amount of water, sun, etc. Why was there such a significant difference in the growth? Further investigation needed to be done.
I pulled the plants out of the cinder-block holes and looked at them. There were new, white visible roots extending out of the bag.
I realized what I was viewing were new root tips - the roots actually grow through the bag and are "air pruned" which makes the roots more fibrous. With increased roots, you get better overall plant growth.
So what was different between the mesh bags and the plants in the plastic pots?
I picked up one of the pots and had to quickly put it back down on the ground. The plastic pot was very hot to the touch - so much so you could not leave your hand on it. Remember, all of these test plants are growing in the same open area - receiving full sun and an equal amount of water.
I found my trusty soil thermometer and decided to take a temperature reading of both the pots and bags. The outside air temperature was 86 degrees F (early August). I inserted the thermometer between the inside of the pot and the media - the temperature on the sunny side of the pot, quite shockingly was 130 degrees! Wow! My media was being "cooked" and you just can't expect good root growth at 130 degrees! Readings taken further in toward the center of the pot had reduced cooler readings. It was logical to assume that as the sun passed around the pots, the temperature would be much higher on the side exposed to the sun. With this being the case, the outside edge of the root system was constantly being exposed to these higher temperatures and root growth would be affected. In essence, the sun was shining on the East, South and West sides of the pot during the day - clearly having a direct effect on three-fourths of the media in the pot.
What about the temperatures in the mesh bags? The readings recorded were a cool 82 degrees F., 4 degrees less than the outside air temperature! Neat - but why? It appears that the block regulates the heat better - it’s about 1" thick on the outside edge, so we have an insulating factor working in our favor. The thickness of the block actually serves to slow the heat absorption into the media. The media in the mesh bags was cool, that in the plastic pots significantly higher.
So what have we learned so far? Plastic pots absorb heat faster, have higher temperatures that move inward toward the center of the media. Roots don’t grow at these high temperatures.
Concrete blocks regulate the heat better. The media stays cooler and the roots can grow and survive. (It would appear the same results during winter, only opposite. The concrete block would also protect the media from freezing/thawing better than a plastic pot.
There are several other benefits we gathered from our test:
1. Plastic pots can blow over in the wind - the concrete blocks don’t.
2. Plastic pots require more water per plant than the blocks.
3. The blocks regulate the moisture better than the plastic pot. When watering, the plant, media and the block all absorb water. As the media dries out, it wicks and pulls moisture from the block back into the media - the same can be true in reverse. If you over-water your media, the block absorbs some of the excess.
4. Plastic pots don’t absorb water - our standard plastic pot had 5 drainage holes located in the bottom so the moisture drains out. This also will require more frequent watering for the plant. Once the media has drained, there is little reserve left for the plant. The media cannot wick moisture back from the plastic pot.
Let’s get back to the key issue for this change in growing systems - the roots!
Common sense tells us the better the root system of the plant, the better the plant will be. The mesh bag roots are "root pruned by air" which will cause lateral branching of the root system. The roots in the plastic pots grow until they get too warm, in our case, we found that roots can be destroyed easily in plastic pots.
Another of the major disadvantages of plastic pots is the roots tend to follow the container shape. So, circular or square pots tend to produce circular roots and examination of pot bound plants will show this to be true. The longer the plant stays in the plastic pot, the more the roots circle until finally you get a root system that looks like a spring. The common name for this is girdling and there are new products out on the market using a copper compound that is coated on the inside of pots to help control this. (New results published show this leaches excessive copper into your soil and based upon what I read, I do not recommend this product at this time.)
Our goal is to produce the highest quality plants possible for you. Plain and simple. The results from the knit fabric container growing system are a "different" method of growing plants. I don’t know any of the "big box" garden centers that would even consider this approach for displaying plants for sale. They use the same old methods of product display. You can’t see the root system of the plants you purchase there unless you pull the plant out of the plastic pot. The only thing you will see is the outside edge of the roots - you have no idea of what the root system looks like back from there. Once you have finished reading this article - you will remember how the heat affects the root growth in plastic pots.
This has been a radical change for us in our growing system from plastic pots to mesh bags. Radical, yes, but no more so than us working to produce native Australia plants in the United States!
There are others in the nursery industry that offer unique Australia plants. I can’t grow everything - but of the plants I do work with - I want to have the very best available for you.
The RootMaker knit fabric container system has proven itself in our trials. I have been so pleased with the results that our production is now focused on providing plants grown in the fabric containers.
I am certain you will be pleased with your results when you order our products grown in the fabric container. It is really quite simple to install the plant - just follow these simple steps:
1. Dig your planting hole, a post hole digger works well.
2. Remove plant from the green RootMaker bag* and then Plant!
3. Water in.
*We occasionally remove the RootMaker bag prior to shipping to save on shipping fees and we recycle these bags.
Bag production in greenhouse operation |
Closer view of production |
Another production view |
Friday June 27, 2003 02:16 PM