Frequently Asked Questions

PRODUCT KNOWLEDGE
The following information gives a basic understanding of what “is” the Growstones™ product.

1.) What are Growstones made from? (Raw Material)
Growstones are made from recycled glass beverage containers received from either the landfill or another source collecting and processing waste glass. The glass containers are first crushed into small glass pieces and then ground into a fine powder (consistent with the size and the feel of flour.) This “glass powder” is the main component of Growstones (up to 99% of the finished Growstones). A natural foaming agent is then added to the “glass powder” before it is heated and expanded in the Growstone kilns. To see photos go to Manufacturing Process.

2.) What is the final appearance and composition of Growstones?
The final product is a rigid porous glass foam which is crushed into irregular shaped aggregates. Growstones aggregates contain approximately 95-99% vitreous soda lime glass (inert glass) with 1.0 - 5.0 % of calcium carbonate, a natural foaming agent. For more detailed information and to view the Growstones MSDS, please go to MSDS.

3.) Do Growstones allow for capillary water rise ?
Yes. In Growstones water raises by capillary action up to 15 cm above the water table. Capillary rise is driven by pore size and pore structure. In Growstones aggregates, mean pore diameter is 98.7 μm (Mercury intrusion) and 79.4% of total porosity are open cells which allow for uniform water diffusion throughout the entire profile.

Because Growstones are an engineered substrate, pore size and pore structure can be manipulated/designed to satisfy grower and crop requirements for more water retention (small pore size) or faster drainage (larger pore size).

4.) What are the physical characteristics of Growstones?

Updated Bulk Density

5.) What is the importance of bulk density of hydroponic substrates?
For all substrates, one of the most important aspects to consider for root growth is the availability of oxygen inside the substrate after irrigation. The bulk density is important because of its distinct relationship with total porosity and oxygen availability in root zone: the lower bulk density, the higher the total porosity. This equates to more aeration for the roots.

Optimum air content for root formation and growth in greenhouses is at least 20 %, and can be as high as 45% (Gislerod, 1982).

Growstones maintain 53% of air at saturation. This facilitates gas exchanges between the roots and the environment around them, leading to higher oxygen and lower carbon dioxide levels – a healthy environment for root growth and development.

6.) How do Growstones moisture/air characteristics compare with other hydroponic substrates?
Growstones have an ideal balance between moisture and air. The graph below compares different hydroponic substrates regarding water holding capacity and air filled porosity at saturation.

At saturation, most substrates enhance either water retention (left on graph) or aeration (right on graph), but not both.
Growstones and Perlite have a great balance between the two. The advantage of Growstone vs. Perlite is a much higher aeration (53 % at saturation) which is not accomplished at the expense of water holding capacity (35 % at saturation). The advantage of Growstones vs. Hydroton is the clear increase in water holding capacity due to aggregates with a high proportion of open cells (79.4 %) which can absorb and hold 35 % of its volume in water by capillary action.

7.) Do Growstones facilitate grower crop management and plant steer ability?
Yes. Steer ability is a measure of easiness of maintaining the crop in balance between vegetative and reproductive growth. The high aeration associated with medium water holding capacity makes it very easy to steer the plant and reach this balance. This is accomplished by controlling root zone moisture content. With Growstones, the root zone can be as dry or as moist as the grower needs it to be, and the desired root moisture content is achieved quickly.
Growstones easy and quick control of moisture content, facilitates steering plants via irrigation scheduling: wetter root conditions from increased irrigation frequency lead to more vegetative plant growth; reduced irrigation frequency leads to drier conditions and promotes reproductive growth (plant tends to set more flowers and develop fruits faster). Plants grown in Growstones respond fast to changes in irrigation scheduling and environmental strategies. Growstones drier nature also helps suppress root diseases such as Pythium, facilitating crop management compared to substrates with high water holding capacity.

8.) Can Growstones be reused?
Yes. Growstones keep their structural integrity over time and contain far less fine particles (or dust) than Perlite or Hydroton. For these reasons Growstones can be reused multiple times. As with any other substrate, sterilization between crops is recommended.

9.) When used in mixes do Growstones float and wash away?
No. Growstones rough and irregular edges help anchoring aggregates to the bulk of the mix - aggregates are kept from floating and washing away with each irrigation.

10.) Are Growstones available in different particle sizes?
Yes. Growstones are available in three particle size ranges. For certain applications Growstones work best with specific particles sizes. The following are the different particle sizes recommended for different applications:

a. Small particle size for propagation mixes – less than 0.079”
(less than 2.0 mm).
b. Medium particle size for soil enhancements – between 1/16"-7/16”
(<8.0 mm to >2.0 mm, with the majority of the particles being between 2.8 mm and 8.0 mm).
c. Large particle size for most hydroponic systems – between 1/2" to less than 1" (12.7 to 24.5 mm).

11.) How does one use Growstones?
This question must be answered in two parts, because Growstones can be used in two very distinct and different ways. The first and most simple way to use Growstones is as a soil enhancement for the cultivation of potted crops, container gardens, flowering beds and/or landscapes. Simply mix Growstones Soil Enhancement into your mix at a 10-30 % ratio depending on plant material and climate. See Products Page for specific information or call one of our technical specialists for recommendations.

The second application is for use as a hydroponic growing substrate/media. These three easy steps will allow for easy use in most hydroponic situations: (1) Rinse by submerging Growstones in a bucket of water (2) Volume of water should be approximately four times the volume of Growstones (3) Discard rinse water in the garden. An easy way to rinse the Growstones is to do it still in the bag. Just make several small perforations on the bottom of the bag and insert a water hose on the top of the bag and allow the water to drain for about 3 minutes.
For detailed directions please go to Labels or call a technical specialist for recommendations.

12.) Has anyone else tested or used Growstones?
Growstone, LLC has invested time and money in testing Growstones. One can visit our Gallery to see images of trials done at commercial greenhouses and universities across the globe.
Research has been conducted at: The University of Arizona, Tucson (2006-2008) and The University of Wageningen, The Netherlands (2006-2007) and University of Arkansas (2008). Field trials have been conducted at: NYC Science Barge, Commercial Greenhouses in Texas, Minnesota, and Florida, as well as by Hobby Hydroponic Stores, Garden Centers and Interiorscapers across the US.

13.) Where are Growstones made?
Growstones are currently manufactured in Santa Fe, New Mexico. As business grows there are plans to open up more manufacturing facilities making it easier for everyone to purchase Growstones.

14.) Are Growstones Organic?
The simple answer to this question is no, Growstones are not organic. The detailed answer to this question is that while Growstones are not organic due to the process of making glass bottles, Growstones can play a vital role in the Green Movement. Growstones can fit into a sustainable agriculture/horticulture program and are definitely part of the foundation of the green movement . . . REDUCE,REUSE, RECYCLE.

15.) How can one purchase Growstones?
To purchase or get a listing of distributors and stores in which to purchase Growstones, please call (505) 473-3997.