Knowledge Center

It depends on your location and growing conditions. If your containers are out of doors in full sun with moderate air movement, then 10 to 12 inches is probably sufficient. If you are growing seedlings in a structure where air movement is limited, you may need to have your wire benches 16 – 24 inches above the floor. If you are seeing roots, even just small tips of roots extending a short distance out of the air-root-pruning openings, you do not have sufficient air circulations or height above the soil surface for your location.

A 12-inch auger works well, especially if it is fitted with a depth control leg that insures that each hole is 7 inches deep, even if the ground is somewhat uneven. I took the “teeth” off my 12-inch auger and sharpened edge of the auger flighting. This gives a clean hole with a flat bottom. If the holes are made 7 inches deep, the top ring of the side ledges with holes are in contact with the surface of the soil and the rest are below the surface. With the ring of loose soil around the holes, and with rain, soil will infiltrate back around the container and fill any voids. Augering works best if the containers are spaced roughly 2 to 2.5 feet in the row and the rows are 6 feet apart. I have also modified a single shank lister plow for installing 5-Gallon Grounders™. This was accomplished by cutting off the 2 sides so that it was about 11 inches across. Then, I welded flat steel plated to both sides. When pulled through the soil, it leaves a trench at the depth you choose and about 11 ½ inches wide. The 5-Gallon Grounder™ fits into the space nicely. After all of the containers are placed in a row, soil is pushed back into the trench between the pots. This works well if the containers are spaced roughly every 2 feet in the row and the rows are 4 or 5 feet apart.

A good soilless mix works best. Because there is little contact between the soil outside and the mix inside, a mix should be used. This is a distinct contrast to the Knit Fabric container where there is a great deal of contact between inside and outside through the thousands of small openings. Remember that the soils must drain well for a soilless mix in the Grounder™ to work well.

At this point in time I know of no shrub, even shrubs that are often grown as small tree forms, that do not grow well in the 5-Gallon Grounder™. The only tree that I do not like in this container is Pecan and that is because the root tips are so large that they do not grow through the openings and instead circle.

A current estimate is that 50% remove the Knit Fabric container and place the trees in above ground containers for finishing. The RootBuilder® container is working well in this capacity. The other 50% are harvesting trees, allowing 3 or 4 days to “cure”, then stretch wrapping the root ball and sending it to landscape jobs. A few are removing the container at the nursery before covering with stretch wrap in order to insure that the fabric is removed at the time of planting. (Note: It is important that instructions are clear that the Knit Fabric container must be completely removed prior to installing in a landscape.)

It is not necessary to ship the plants in the RootBuilder® container for the root ball to stay together because the roots are so fibrous. The technique that both customers and nurseries are pleased with is to lift the trees at the nursery, remove the RootBuilder® container and cover the root ball with black stretch wrap. This gives the nursery the re-use of the container without the fuss of deposits and returns, and the customer will have less to handle and dispose of at the landscape site. It is best to use black stretch wrap. Clear stretch wrap will cause a “greenhouse effect” that will accelerate heating and lethal root temperatures could be reached.

For Knit Fabric, in-ground, containers the spacing should be roughly 4 foot centers for nearly all species. Consider the growth and development of trees in 12 or 14-inch containers versus 18 inch. Trees in 12 of the 14-inch containers will typically be harvested when the stem diameter is 2 inches. For trees in 18-inch diameter containers that are going to be grown to a larger size (one more growing season) the removal of the lower limbs should begin at this point. As the longer lower branches are removed, the branches at a point roughly 4 feet above the ground are not as long and therefore can be left to grow another growing season without appreciable interference with each other. On the other hand, if 24-inch diameter Knit Fabric containers are used, the spacing should be about 5 to 6 feet on centers to allow for proper branch development on a tree of 3.5 to 4.0 inch stem diameter. As for spacing between rows, 10 feet is very workable for most species. The only reason to use rows wider would be if your machinery were of a larger size. Spacing trees 4 feet in the row and 10 feet between rows provides approximately 1000 trees per acre. Remember that most plants have developed methods that allow leaves in the inner branches to function similarly to those in full sun. There are only a few species that are particularly sensitive to shading by an adjacent plant; those are primarily the pines, and other conifers and particularly bald cypress.

There is nothing wrong with germinating seeds in flats then transferring seedlings to RootMaker® trays – as long as it is done when the seedlings are quite small. This is what I practice at Lacebark for many of the species I work with – and primarily because seed germination can be so unpredictable and in order to get 32 of the same size in one tray, compared to a few big ones that over shadow the smaller ones.

Tree seedlings in RootMaker® II propagation containers are routinely taken to the field when they are 12 to 16 inches tall and 3 to 4 months old. This has been done by hundreds of nurseries across the country. Most do fall planting – September or October and some have drip irrigation and others do not. (Drip irrigation assures nearly 100% survival. But even without drip irrigation, the success rate is quite high, except for the occasional severe drought immediately following planting). The primary reason for planting tree seedlings at a larger size is that in the small growth stage, telling seedlings that will make winner trees from culls is tough and the cull rate may be as high as 25 to 30% or more for the oaks. In one gallons, the cull rate drops to 7 to 10% and with 3 gallons to 2 to 3%.

Determining the optimum time to remove seedlings from containers will vary season to season and at your location versus another grower. Remember, it is always better to remove seedlings early, even if this means a small amount of mix falls away, versus leaving the plants too long. The plants were difficult to remove as a result of two factors: 1. They ran out of space for additional root growth. There are sequential flushes of roots as root tips are air-pruned and secondary roots are produced. With the production of the third flush of branch roots, there is little additional space for these new roots to exploit, so they fill any remaining small voids. 2. As the seedling grows on top, so do the roots, both in numbers as a result of air-pruning, but also roots grow in diameter. It is primarily the increase in diameter of the roots that puts pressure on the sidewall of the container and makes removal more difficult. In the future, consider transplanting seedlings just as the root ball can be easily removed and into a container large enough to support additional root growth for the rest of the growing season if space and overwintering are factors or into the next step up in container size relative to your production goals. Think of transplanting like driving a truck---- If you make timely transplants, you keep the plant growing, what I call "full throttle". On the other hand, if you leave the plants too long and they approach or come to a full stop, it takes considerable time and wasted energy to get growth rolling again.

Some root pruning is better than none. To maximize the root pruning efficiency, one might consider the RootBuilder High 5. Be sure to cut any circling or kinked roots on the outside as you transplant from a conventional pot to a RootMaker.

Osmocote or similar coated slow release N,P,K fertilizers work best. For example, even though on the bag, Osmocote 18-6-12 says 8 to 9 month release, on or in the soil, this product will slowly release nutrients for two growing seasons. The reason is that Osmocote and most other coated slow release products release based on temperature and the calibrations are for when they are used in above ground containers. Because on or in the soil is much cooler than a container, the release of nutrient is much slower and therefore over a much longer time. This also means that more is needed to be applied initially since it is slower and releases over a longer period of time. Not only is the slow release desirable and little if any is lost to leaching, it is very safe and one has to nearly mulch a young plant with Osmocote in order to cause injury or burn. Osmocote and similar products are more expensive, but in light of the safety and you only need to do it once for the growing season, in my opinion, they are worth the extra cost. This is what I use personally when planting individual items in the field or landscape. I typically apply about 1/4 pound over an area about 2 feet by 2 feet, because from my research roots will extend out much faster and further that is generally realized. And it is important to remember that when trees are grown in the green knit containers in the ground, root growth outward is not restricted initially. Only after the root has grown out and is absorbing nutrient and increases in diameter, does the girdling occur at the small openings to block most of the sugars from the leaves from going back out to the root tips. I describe the roots outside the fabric wall as nurse roots, they contribute substantially to growth of the young tree, yet when the tree is harvested and transplanted elsewhere, the loss of those outside roots is of minor consequence. Organic fertilizers are also good. Organic fertilizers cover a huge range and some are very good products and others are of minimal value. They are quite safe and it is difficult to damage or burn a young tree with organic fertilizers. The organic fertilizer I have had the most favorable experience with is Milorganite. This is a modified sewage sludge out of Milwaukee, WI and is widely used by the golf industry on greens and tees because of the performance and safety. In this case follow the rate instruction on the bag. I DO NOT recommend using dry chemical quick release fertilizers on small trees as it is difficult to get the rate per unit of surface area correct. After applying the 100 pounds of nitrogen per acre rate in the field, then looking at the dispersal of the granules, it does not look like very much. And, as a result, when applying dry a chemical fertilizer around young plants it is tempting to apply more, since the proper rate looks like so little. Just last spring, because I was out of Osmocote, but a rain was forecast so I fertilized about 25 young pine trees 3 to 4 feet tall with the 28-4-5 chemical fertilizer we use in the field and proceeded to damage 11 of them because I applied too much relative to conditions at the time. In my case, I applied the fertilizer, the next day we got about 1/2 inch of rain which was enough to dissolve the fertilizer and move it into a limited volume of soil, then it turned off dry and it was 13 days before any more rain fell and these trees were located such that they could not be irrigated. The concentrated fertilizer caused a salt burn to roots near the surface as the soil dried out and caused partial defoliation --- and this is after conducting research in the area for nearly 50 years. So, yes, dry chemical fertilizers can be used, but be careful as it is very easy to get too much. Here at the research farm we do use a dry, quick release chemical fertilizer with analysis 28-4-5 but only on our field soils. This fits our needs well and has performed well in our field soils over the years. We broadcast this down rows of trees in the field in a band about 6 feet wide and at a rate of about 100 pounds of nitrogen per acre once in the spring and it lasts all season. This is because our soils have a hard layer down about 12 to 16 inches that makes drainage slow but adequate for the many species of plants we are working with. If soils are sandier and drainage is greater, applying the same amount per season, but applied in two applications would likely work better. Applying 100 pounds of nitrogen per acre of soil surface means spreading roughly 350 pounds of actual material out of the bag. With a fertilizer spreader that has been properly calibrated, this works well and requires a modest amount of time.