I am thinking about starting a greenhouse for roses. I have two questions that maybe you can help me with.
How many gallons of water do I need per square feet on an annual basis?
Is there a spreadsheet type of tool that I can use to get a better insight into the amount of nutrients I need?
Is there a cost/butget tool that can provide me insight into the finances of growing roses?
Thanks for your help!
Best wishes
Josh
I’m not sure how much greenhouse experience you have. Under cover is a bit different from outside. But I can give you some geneeral rules based on the physiology of plants. Most all plants that use what is called the C-3 photosynthetic pathway, including roses, will use a half liter of water for every gram of dry matter that they produce. That is the minimum. If you include evaporation from the soil it might be twice as much when the plants are spread out a bit on the ground. If you prefer, think of how much rain it takes to cover the ground and suppose the roses are completely closing their canopy. One meter or rain (39 inches) is 1000 liters/m2 or 250 gal/sq yd, roughly speaking. If your greenhouse is not too wide open most of the season that might be a reasonable guess. IF you add a heating system and grow year round you might grow twice as much plant material and use 2x the water. I doubt you can do more than that. Irrigated alfalfa in Arizona, saltcedar or eucalyptus might reach 3 m/yr but that’s pretty uncommon. So I’m suggesting you might grow 2-4 lb of rose matter/sq yd, if you have a dense bed of say minifloras that never stop blooming. Roses in Balboa Park, S.D. CA might be that productive too. I don’t know if anyone has ever weighed them but I expect there are commercial rose producers who actually know the numbers for their particular place.
Once you eliminate the water stress, nutrients will be needed in considerable quantity, based on how much biomass you are producing and the exact nutrient content of that biomass. For instance for potassium you might have 1% in the plant so you’ll need around half an oz (14 grams) for the production on 1 sq yd at optimum growth. Maybe an oz. The people who run greenhouses professionally have it figured out for all kinds of crops. There are books on the subject. Very likely a lot of websites too on things like tomatoes on continuous-recirculating systems with automatic nutrient sensors and pumps to replenish the solution. Good luck. Let us know what you find.