Frequently Asked Questions

Green Roof:

Can we mix it ourselves on site?
This is not recommended because of contamination concerns and quality control.

Why so little organic matter?
There has been much debate over the quantity of organics that makes up the media. Organics will decompose creating two specific problems. First, if the percent of organic matter is too high, the volume of mix decreases due to decomposition, requiring replacement due to the displacement of the media. Second, as the organics break down, the fines filter out down to the separation fabric. Once settled on the filter fabric, the organic fines decompose further creating a slime, which may impede the drainage causing the water to build up in the media. This may create plant health problems and possibly increase the structural load. No more than 10% to 20% of the media should be organic in humid regions.

Is it alright to use "bio-solids" as the organic component in my green roof media?
Stalite does not permit the use of bio-solids in the specifications for a number of reasons. Certain biosolids (sewage sludge compost) may have a limited acceptance for horticultural use. Certain composts may be derived from feedstock’s that may include biosolids from municipal sewage treatment facilities. These sources may contain very fine particulates, heavy metals, pharmaceuticals, hormones, and pathogens. Biosoilds must be sampled and tested for any health and safety related parameters (state or federal). Fine particles from the agents used during the “dewatering” process of the raw sewage may include lime or flocking agents. Finer particles tend to filter down through the mixture and cake up and clog filter fabric. Green roof media is designed to drain well and the affluent from the roof may be discharged into a creek or other body of water during which the heavy metals (arsenic, copper, nickel, cadmium, lead, mercury, and zinc) that may be contained in the biosolids may leach out of media and enter a sensitive watershed.

I received a growing media that looked like it had peanut shells in the media, is this ok?
Peanut shells should NEVER be used as a bulking agent for compost. Anyone with peanut allergies coming in contact with the material could have a dangerous reaction to the peanut shells. Also certain detrimental nematodes have been known to be passed along in the soil attached to the shells.

What is German FLL? And does Stalite meet their guidelines?
The FLL is a German non-profit organization that has put forth a set of greenroof guidelines and labor instructions for the evaluation of research results and technical information of commonly accepted tests, requirements, definitions, and testing methods. Though products in the U.S. are not required to be certified as they are in Germany, Stalite has been tested by an FLL certified independent lab using the FLL methods and Stalite meets all their criteria.

Structural Soil Trees:

What is the difference between our mix and others (Cornell)?
There are two main differences: 1. CU uses a quarried rock like granite, limestone etc. 2. CU uses a Hydrogel product that coats the rock during mixing, since Stalite holds water Hydrogel is not needed during the mixing process.

How small can, or how large can the planting pit be?
For large trees 3 feet deep is recommended and a rule of thumb is the size of the area for structural soil should be 2 cubic feet for every 1 square foot of crown projection. On some projects a 3 or 4 foot wide trench is dug the entire length of the side walk connecting the tree pits and filled 3 feet deep with the structural soil.

Do you need air vents?
Air vents are optional. It depends on the amount of paving that surrounds the individual tree. Air vents allow access to roots under pavement for future fertilization and watering.

Can I plant the trees before pouring concrete or placing pavers?
No. We have always specified that the tree(s) be planted after concrete / paver installation. Lime leaches out of concrete and elevates the pH of pre-placed tree pit media. Planting after pavement installation reduces the likelihood of planting media contamination and mechanical injury to the tree(s). By following our guidelines the contractors are able to install the root ball at the proper finished elevation, reducing the likelihood of tree root collar burial.

Should I stake the trees in wind prone areas?
Yes, but make sure the lines are checked and the guying is removed after one growing season.

Root Bridging:

Do I have to use porous paving materials on top of the root bridge or can I use air vents?
Porous pavement is a good practice if maintained properly, however any pavement method can be used. The air vents are optional but do come in handy for future watering and liquid fertilization to the root zones.

Is there a limit as to how deep the root bridge can be and Can the root bridge material go right up against the tree?
We have placed up to six feet of Stalite on the roots and have actually seen improvement in the health of the tree. We do not recommend burying the tree trunk in any media but do recommend using a retaining wall or tree well in these particular situations.

Can I plant grass or ground covers over the root bridge?
Yes, simply place PermaTill structural soil for turf over the root bridge and plant it. Irrigation will be needed to prevent drying out.

Landscaping/Soil Amendment:

How does PermaTill affect the water needs and leaching of fertilizer from the root zone?
PermaTill does improve drainage, however, the particles are 6% absorbent for moisture storage. The particles also have a high CEC or nutrient holding capacity (26.9) so the particles will store the water-soluble nutrients for the roots to take up. Remember this: Roots follow moisture down into the soil. They grow at the surface when there is not enough air present deeper in the soil. With PermaTill amended soils the roots will stay deeper and therefore reduce water needs and your water bill.

Why not just add compost, soil conditioner, or even peat moss to improve aeration of tight soils?
Compost and soil conditioner are great soil additives especially in soils that have little to no organic content. In fact, it is essential to maintain beneficial microbial activity in the soil. However, it decomposes over a season and soils compact again Organic amendments absorb water and if soils can’t drain properly then you have conditions ripe for anaerobic activity which causes soil and plant diseases. PermaTill has a high water release capillary action that means the particle reserve over 90% of their pore and cell spaces just for air.

Why not use gravel as a soil amendment for drainage and aeration?
Gravel is not porous and once the clay soil particles compact between the stones the air spaces for roots and drainage disappear.

Structural Soil for Turf:

Can you park on it daily?
The structural soil will hold up fine, however the root crowns of the turf will be damaged from excessive compression. It is designed for occasional use, otherwise we recommend the addition of turf rings.

Is it too coarse for athletic playing fields?
It is fine for the turf fields when sod is placed on top of it, but Stalite is way too coarse for baseball infields or topdressing.


What makes Stalite better than regular stone for this application?
The Stalite contains voids for additional surface area for fine feeder roots, air space, water and nutrient retention. With its high water release curves and cation-exchage-capacity of 20 to 25 me/100g, roots can grow in 100% of the expanded aggregate without added soil. Plus it is lightweight and easy to mix and work with.

What is the pH and does Stalite leach any minerals into surroundings?
The pH of Stalite is about 8.5 which is very beneficial for bio-retention due to the acidity of runoff. Stalite does not leach any minerals or contaminants but actually helps with the remediation of the nutrient load and hydrocarbons from runoff.


How does the pH (8) of PermaTill affect acid loving plants?
PermaTill is inert; therefore, it does not affect the soil pH. Just use the appropriate fertilizers and top-dress with composted pine bark fines to maintain the proper pH for the plant(s).

Can I use PermaTill in the greenhouse to root cuttings?
In greenhouse tests PermaTill outperformed all other rooting media. However, the cuttings were under mist systems. Without mist systems we recommend combining PermaTill with other components like vermiculite or milled sphagnum moss to ensure enough moisture for the developing root system.


Are PermaTill and VoleBloc the same thing?
Yes. There are parts of the country that have vole problems but no heavy clay soils. Therefore, like many other product lines we labeled the packages directly to the customer needs. The 40 lb. PermaTill bag is labeled very well for both uses.

For vole control can I just till it in around perennials and shrubs?
For effective vole control a solid ban or barrier of VoleBloc must be installed all the way around the root zone, 8-10” deep to the soil surface with a VoleBloc layer around the stems. Voles are persistent tiny rodents that can maneuver through 2-3” diameter holes. Do it right, according to the directions and you’ll only have to do it once.

Why not use gravel for a vole barrier?
Gravel may be somewhat effective but it does not have the sharp edges that the VoleBloc particle have and that voles detest.