Virtual Grower 3: A Powerful Decision Support Tool for Greenhouse Systems By Jonathan Frantz

Growers are exceptionally talented at figuring things out. Knowing a crop, a greenhouse production system, a market — it all blends together. And when it all blends together perfectly, growers can anticipate problems, solve them before they create setbacks, know instinctively when to plant different varieties to hit a sell date, and understand how it all works together.

Except when it doesn't work out that well.

Several years ago, our group released the Virtual Grower software to the public. Initially designed to help greenhouse growers determine heating costs and do simple simulations to figure out where heat savings could be achieved, it has slowly added features so that now, Virtual Grower can help not only identify those savings through different greenhouse designs, but predict crop growth, assist in scheduling, make real-time predictions of energy use, and see the impact of supplemental lighting on plant growth and development. In other words, the software can be a safety net and allow users to experiment with "what if" scenarios in a risk-free setting.

New Features and Improvements

Virtual Grower 3.0 is the next installment in the software series. Released in August, 2011, this version is the first to be both Mac- and PC-compatible, meaning no one is excluded from being able to use the software. Return users will find the same easy-to-use sections for designing greenhouse structures, heating systems and lighting systems, and adding up to 40 plant species or varieties to your simulation.

Need to know when to start a crop? Users can now enter a target finish date and "backtrack" to predict when the crop should be started from plug stage. Was your location not included in the previous versions? The new version has nearly 800 locations across the United States represented by their weather, which is an increase of more than 500 sites. Do you have a complex heating system? Virtual Grower 3 can now accommodate dual-stage heating systems and apply them to as many greenhouses as you want. This allows for the simulation of the increasingly common case of having a very high-efficiency system running most of the time and a lower-efficiency, less expensive system supply heat when additional heat is needed during cold periods. Not familiar with all of the crops? Students in the greenhouse industry can view photographs and track down additional information for all of the crops included in the software. All of these features are bolstered with graphics including a location map, photographs, responsive schematic drawings of your simulated greenhouse, and graphs and charts of the output (Figure 1).

As existing features are improved upon or new ones added, the software becomes more complex. Our efforts in supporting the software are increasing in line with the software development. Up until now, people who have had questions or encountered problems with the software have been able to reach Bryon Hand, the software developer behind the program, or me through the email help desk: We have worked with many growers, students and allied industry professionals through this service and follow-up phone calls to solve each person's issues. Our training for the software had been limited, unfortunately, to a handful of face-to-face sessions at trade shows such as OFA. With the efforts of Deanna Bobak on our team, a series of short (3 to 5 minutes) video tutorials were developed that walk users through the basics of Virtual Grower 3. These videos will be available online.

Case in Point

So what can it do for you? A test case:

A grower in western Michigan has an older greenhouse structure and wants to upgrade. In the wintertime, he does an excellent job of fixing leaks so no cold air seeps in, but there are times when his unit heaters just can't seem to keep up. He feels he has great quality crops but wants to improve on his light, hoping he can get even larger, faster growth for his bedding plants. Complete replacement is expensive, so should he upgrade the existing system with a high-efficiency heater and add supplemental lights or start from scratch?

His three-span greenhouse has 9,375 square feet of floor space and is made of glass. It is unfortunately of older construction, so the glass panes are smaller, which cuts down his light entering the greenhouse. His natural gas-fed unit heaters are older, but he maintains them once a year — it is difficult to do it more often since they are above his benches. He heats his greenhouse beginning in December for plugs, then moves into finishing plants; his season begins in December and ends at the end of June. His heating costs are estimated to be $6.05 per square foot or an average of $0.20 per square foot per week if he pays $1.25 per therm of natural gas. Table 1 shows his typical crops, how long it takes from plug stage to produce a finished crop (starting on Feb. 1), and how large the plants were at flowering.

In a simulation for supplemental lighting, adding 60 800-W high-pressure sodium lamps (20 lamps in each span) would boost his light considerably, which could boost his plant quality. If he uses day-length extension for up to six hours and the lights only come on when the light inside is lower than 200 µmol m-2 s-1 (about 1,000 foot-candles), those lamps could provide an additional 100 µmol m-2 s-1 (about 500 foot-candles) during that period. This additional light results in an added cost of electricity of $1.22 per square foot at $0.11 per kW-h, or slightly over $0.04 per square foot per week. Adding lamps increased plant size at flowering, so plant quality may have changed with supplemental lighting, but flowering was not accelerated.Upgrading his heating system to a high-efficiency system could also save money. He also wants to put the heating systems closer to the plants — after all, why heat all the upper portion of the greenhouse when the plants are on benches below the heaters? And now that they are more convenient, he can check on them monthly. A simulation of upgrading his heating system in these ways drops his heating bill for the season to $4.47 per square foot or an average of $0.15 per square foot per week.

A new facility could allow for a number of changes. A newer structure would allow for additional lighting (larger glass panes = less shading), which could reduce the need for supplemental lighting. And a new facility could allow for additional heating system efficiency gains. In a simulation of a same-sized facility that boosts heating system efficiency by 5 percent above the new unit heater upgrade, costs without supplemental lighting are now down to $2.78 per square foot during his season or an average of $0.09 per square foot per week. The new facility also resulted in a substantial change in rate of flowering, with up to two-week acceleration with pansies in this new facility. Changes in plant size at flowering suggest that changes in plant quality occurred as well.

The additional light from the simulated new structure only slightly reduced his supplemental light electric bill, dropping it to $1.18 per square foot for the season or just under $0.04 per square foot per week. If he were to add supplemental lighting in his new facility, it would not further change rate of flowering, but would be expected to increase plant size at flowering, indicating plant quality could be changed.

Should he renovate or replace? Only the grower can decide for certain, but now he can quickly run the simulations himself and get immediate answers rather than leaving it to chance and finding out after a decision is made if that decision was a mistake. Now that more parts of the system are integrated (structure with heating with plant growth), he has more information about ongoing expenses at hand to consider in his decisions. With this information, he can see how plant timing and quality will be impacted by a new facility, perhaps resulting in a higher quality product.

Got Feedback?

Like it? Don't like it? Wish we would change something? We want to hear from you. Most of the features that are in the software now came from users like you. This is an ongoing project with no expiration date, so your suggestions will be considered and hopefully incorporated into the next version. For example, we hope to start incorporating information about sustainability or "footprint" tracking, but we like to think of everything within a greenhouse system as fair game for inclusion. As always, people want more plant species to simulate, and thanks to efforts from researchers at places like Michigan State University, we continue to add more species regularly. Previous versions of the software were translated into Spanish and French and we plan to do the same with this version.

If you'd like to try it or just replace an earlier version, you can obtain a free copy by going to Follow the download instructions and start your simulations! This research would not be possible without the ongoing support of programs like the Floriculture and Nursery Research Initiative, a federally-funded program within the Agricultural Research Service that targets research with potential to provide substantial economic impact to both floral and nursery industries.

Jonathan Frantz

Jonathan Frantz is a research horticulturist with USDA-ARS. He can be reached at

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