| Safety | High pressure system appears safe. Storage bottles will need to be inspected/tested regularly, hydraulic hoses need regular inspection (similar to stump grinder). Operator is 12+ inches from high pressure system, safety shield can be erected if needed. | One potentially serious accident in California; problem has been corrected. Operator’s chest is 6 inches or less above top of machine. |
| Safety equipment required | Hardhat, face shield, hearing protection required. | Hardhat, face shield required. Hearing protection for drill/generator and compressor recommended. |
| Crew training time | 4 hours + | 2 hours or less |
| Speed | Average 3 minutes/hole; discharges at two levels per site, 2 liters of fill discharge. | 10-12 person minutes/hole using 1 discharge per hole, and 2 liters of fill. |
| Crew size | 1 or 2 people | 2 people - operator must be able to lift heavy loads (40-60 lbs.) repeatedly. |
| Frequency of repair | 8 problems in 15 hours of operation. 3 did or could stop operation for 15-30 minutes; 2 of these serious problems have been designed out in new version. | 0 mechanical problems in 20 + hours at Bartlett Tree Research Lab. Parts readily available. |
| Suitable for multiple operators | No - requires well trained operator. | Yes |
| Fill material | Will accept styrofoam ‘C beads, perlite or vermiculite; will not accept fine water absorbing polyacrylimide in moist environment, will not accept peat with large particles; may accept course water absorbing polyacrylimides and fine peat (not tested). | Will not accept peat with large particles. Will accept all other tested materials. May accept fine peat (not tested). |
| T ransportation | Requires trailer or full size pick-up truck with ramps. | Full size pick-up truck is suitable (must tow heavy compressor). |
| Property access | Climbs 20+% slope; jumps curbs with difficulty. | Must be within air hose distance of compressor (50 or 100 feet increments). Hand carried over any terrain. |
| Operation under low limbed trees | Requires 6+’ of overhead clearance. | Drill and operator more limiting than machine. |
| Terrain | Climbs 20+% slope, outrigger requires close to level soil. | Requires “20” diameter circle of flat surface, Tufts of grass may interfere with operation. |
| Recommended options | Heavy duty engine (Kohler), US manufactured air powered wheel motors. O-ring free main control valve. | Slightly less than 2” diam. drill bit. Lighter weight (aluminum) model ‘Grow Gun Lite’. |
| Approximate cost | $18,500 - 26,000 | $3,000 - Grow Gun - Steel |
| $4,000 - Grow Gun Lite |
| $50 - Auger $250 - Gas Drill or Generator rental |
| $12,000 - Compressor or $50-75/day rental |
| Major advantages | Speed, able to fracture soil at multiple depths. | Low initial cost without compressor purchase. Low repair cost. |