Sizing a hydroponic system
Once you have made the decision to grow hydroponically, your focus should turn to planning for your new system. Last week, we covered the top factors to consider when venturing into hydroponic crop production. We discussed how important it is to know your market, crop production goals, size limitations and more before purchasing your system. If you have not already reviewed this topic, you can find a link to it here. We suggest reviewing the topics for consideration before sizing your system, as having answers to our top considerations list can help provide you with more accurate numbers, making your overall system sizing process much more precise.
Sizing a NFT System
As one of the most popularly produced crops in a NFT system, for this example we will be referencing lettuce. The trick to properly sizing any hydroponic system is to take your time, plan ahead and work backwards.
On average, lettuce requires 50 days to go from seed to harvest, which means it takes approximately 7 weeks to become harvest ready. Factoring in 2 weeks in a nursery system leaves us with 5 weeks that the lettuce will remain in the NFT channels.
50 days / 7 days per week = 7.14 weeks
7 weeks – 2 weeks in nursery = 5 weeks in NFT system
As an example, our production goal is 500 heads of lettuce per week. To find the number of plant sites our system requires, we need to multiply our weekly production goal by the number of weeks that the lettuce will remain in the system.
500 heads per week x 5 weeks = 2,500 plant sites
With such a large plant site requirement, an operation such as this would be best suited for two sections of channels, with 1,250 plant sites per section.
2,500 plant sites / 2 sections = 1,250 plant sites per section
With our plant sites and harvest cycle now discovered, the next step is determining our plant spacing. We recommend 8 inch spacing on center for lettuce and leafy greens, meaning that each plant site in a single channel should be located 8 inches away from one another. Our NFT channels are available in 8, 10 and 12 foot lengths, with the 12 foot length being the most efficient for production on this type of scale. To determine the number of plant sites per channel, first multiply the channel length by 12 to determine the channels length in inches.
12’ channel x 12” in a foot = 144” channel
Next, divide the channel length in inches by 8 to account for spacing. This will reveal exactly how many plant sites each channel will hold.
144” channel / 8” spacing = 18 plant sites per channel
Knowing the plant sites per channel, we can now move to determining how many channels are required for our system. To do this, take the plant sites per section number from earlier and divide that by the plant sites per channel. Since our example system will be divided into two sections, we will determine the number of channels needed per section then double that number to determine how many channels will be needed in total.
1,250 plant sites per section / 18 plant sites per channel = 69.45 channels *round up to 70
70 channels per section x 2 sections = 140 channels in entire system
With the plant sites, spacing and channels now properly determined, the final step is determining how much total space in our grow room is required for the sections of channels. To find this figure, we must first uncover a rather unexpected denominator. To find this important denominator, it is important to remember that 8 inch spacing is recommended on all sides. This means that your plant sites will need to be staggered from row to row in order to allow proper spacing on the front, back and each side. With this in mind, divide the 12 inches in a foot by the 8 inch spacing that is required. This resulting number equals how many channels you will have in a given 12 inch span.
12” in a foot / 8” spacing = 1.5 channels per 12” span
With this denominator realized, we are now able to determine the overall width of our channel sections. To find the width, take the number of channels that are required per section and divide it by 1.5.
70 channels per section / 1.5 channels per 12” span = 46.6’ *round up to 47’
Given that the channels are 12 feet long, we now know that each section of our NFT system will measure 47’ Wide by 12’ Long. This size system will provide us with 2,500 plant sites and our expected harvest of 500 heads of lettuce per week.
Once your system has been properly sized, you now know just how much room your system requires and can therefore plan accordingly to include walkways, nursery space, reservoir tanks, pumps, heating, cooling and more. If you are working within an existing space, you may find that you do not have the room required to properly and safely meet your desired production needs. If this is the case, you can always size down your production goals or invest in a greenhouse or growing space that will provide you with enough space to meet your goals. It is better to discover this in the planning stages and not during the installation phase.
Sizing a Dutch Bucket System
For our Dutch Bucket example, we will be planning our design based off an indeterminate or vining type tomato crop. As with the NFT system, we again recommend working backwards, determining your production level first, narrowing down your exact system size last. Tomatoes and most other fruiting crops are typically a longer term crop, requiring more time in the nursery and a longer vegitative/blooming phase. The reward for these crops however, is an active fruiting period in the area of 9 months.
For our example, we will be anticipating a harvest of 3,000 pounds of tomatoes per month, equaling 36,000 pounds of tomatoes throughout the entire year. On average, a single tomato plant will produce roughly 5 pounds of tomatoes per month.
Our first goal is to determine how many tomato plants we will need in order to achieve our production goal. With a goal of 3,000 pounds of tomatoes per month and an average tomato plant producing 5 pounds of tomatoes per month, we need to divide 3,000 by 5 to determine how many plants are necessary.
3,000 pound tomato harvest per month / 5 pounds of tomatoes per plant = 600 plants
For a Dutch Bucket, we recommend two plants per bucket to allow for proper watering and nutrition. To determine how many Dutch Buckets are needed for your system, divide the total number of plants required by two, since each Dutch Bucket can hold two plants.
600 total plants / 2 plants per Dutch Bucket = 300 Dutch Buckets
We will be looking to grow our tomatoes within an existing 30 foot wide greenhouse. To ensure that we have enough space to meet our production needs, we now need to determine the total space our Dutch Bucket system will require. To do this, we need to determine the width and length of the system itself. We recommend 6 foot row spacing for Dutch Buckets, with 16-18 inches in-row spacing. The 6 foot row spacing provides spacious walkways that allow for plenty of room to harvest, pollinate and prune the crops, while the 16-18 inch in-line spacing offers enough room for each plant to grow to full size without tangling with one another.
Following our example, we will want to determine how many rows of Dutch Buckets are required. To find this, we will divide the width of our greenhouse by 6 feet, which represents the between row spacing.
30′ Wide greenhouse / 6′ row spacing = 5 rows of Dutch Buckets
5 rows of Dutch Buckets = 4 walkways
4 walkways x 6’ per walkway = 24’ Wide Dutch Bucket system
With the number of rows and width determined, we can now find the systems length. For this, divide the total number of Dutch Buckets needed by the number of rows that will be in the greenhouse.
300 total Dutch Buckets / 5 rows of Dutch Buckets = 60 buckets per row
Next, multiply the number of Dutch Buckets in a single row by 16, which represents the 16 inches of in-row spacing.
60 Dutch Buckets per row x 16” in-row spacing = 960” row length
960” row length / 12” in a foot = 80’ row length
After determining our systems length, we now know that our system would measure 24’ Wide by 80’ Long and can plan our greenhouse design accordingly.
With proper planning and the use of simple math, sizing a hydroponic system is a rather easy process. Always remember to work backwards when determining your systems size and plan for things such as walkways, work areas, water tanks and other items that are essential to your operations success, but may take more space than originally anticipated. Planning ahead can help save you a great deal of time and hassle, preventing you from working with an oversized system that does not fit your growing environments needs or your production needs. If you are considering growing with hydroponics, try our tips and advice for sizing your system and contact one of our hydroponic specialists to ensure every detail of your growing operation has been covered. Plan ahead and you will be rewarded with a bountiful, year-round growing operation.
Learn more on our complete line of HydroCycle hydroponic systems, GrowSpan greenhouses, hydroponic accessories, environmental controls and more by visiting our website, FarmTek.com. You can also join us for a three-day CEA Hands-On Workshop, during which we discuss sizing a system along with topics such as greenhouse design, greenhouse climate control, nutrient management, integrated pest management and more.