Crop scheduling
Planting all the crops on a farm at the same time results in production waves instead of continuous production. Continuous production is what farmers need in order to satisfy weekly or even bi-weekly demand, by always having mature crops in the farm. A planting and harvesting schedule that accounts for the life cycles of each crop is a useful tool to achieve this (Storey 2016c):
Leafy greens like chard, lettuce, and cabbage have a 4-6 week cycle from transplant to harvest
Quick herbs like chives and mint have a 3-4 week cycle between harvests
Coriander, parsley, and basil have a 5 week cycle when conditions are right
Fruiting crops such as strawberries and tomatoes produce continually. They can therefore all be planted at the same time
It is also important to consider the effect of harvesting the plants on the entire ecosystem of the aquaponic unit. If all of the plants were to be harvested at once, the result would be an unbalanced system without enough plants to clean the water, resulting in nutrient spikes. Some farmers use this technique, but it must correspond with a large fish harvest or a reduction of the feed ration. However, it is recommended to use a staggered harvesting and replanting cycle. The presence of too many plants growing synchronously would result in the systems being deficient in some nutrients towards the harvest period, when the uptake is at a maximum. By having plants at different growth stages – some seedlings and some mature plants – the overall nutrient demand will always be the same. This will ensure more stable water chemistry, and also provides a more regular production (Somerville et al. 2014a).
While indoor growers enjoy the benefit of year-round harvests, they can still lose precious time when their system is empty between crop cycles (downtime). In order to minimize downtime, seedlings need to be ready to transplant to the aquaponic system when the previous crop is ready for harvest. This can be done by calculating the number of days in advance that you should germinate new seeds so that they are ready to go into the system on the day you are ready to plant. Use a calendar or Gantt chart and follow these steps (Godfrey 2018):
– Mark harvest day
– Add together your crop’s germination time and propagation time. This will give you the number of days prior to harvesting that you should start germinating seeds for the next crop cycle. Count back on the calendar, and mark the day you should germinate your seeds and the day you should move them to propagation. The day you transplant into the system should fall on the day immediately after the harvest of the previous cycle. Depending on the size of your system, you may be able to harvest and transplant on the same day. If you have a large farm, it may take you a few days to harvest.
Environmental conditions and crop variety will all influence crop timing. Figure 7 shows a hypothetical crop schedule for a lettuce variety where the whole plant is harvested (as opposed to a cut-and-come-again variety). The five day germination time is followed by a 16 day propagation time, at which point the seedlings are ready to transplant into the aquaponic unit. After a further nine days of growth, the lettuces are ready to harvest. The second crop cycle is timed so that the seedlings are ready to transplant into the aquaponic unit on the same day that the first cycle is harvested, thereby minimizing downtime.
Figure 7: A hypothetical crop schedule for lettuce
Using overlapping crop cycles, as in the example above, produces a small harvest each week, rather than a large one every five weeks. This is an obvious strategy to use for a farmer with a contract that states that they promise to deliver a certain amount of produce every week. The steps for creating an effective scheduling plan are as follows (Godfrey 2018):
Make a labour plan for harvest – If you will be harvesting by yourself, make sure that you have enough time to harvest everything you need to in order to have it ready on time for the sale
Know your varieties – Each crop has different cycle timing, so make sure you read up on the unique requirements of the crop. This will inform all of your decisions, from germination to harvest to delivery. In addition, consider what type of harvest the plant will require. For example, lettuce will probably be fully harvested, which will mean that you would need to replant sooner than if you grew something like basil where you could harvest the same crop cycle multiple times
Choose your harvest technique – How you harvest should be determined by your crop type; some crops allow you to use cut-and-come-again harvest while others are more suited for a full harvest. A cut-and-come-again-style harvest will probably take longer than a full harvest technique, because you will be cutting the same plant multiple times rather than taking the whole thing in one go
Factor in the size of your farm – The bigger the system, the longer it will take to harvest. That is a general rule, even if you have employees working for you. Labour is one of the largest costs of running indoor farms, and because things just take a long time. Ensure that when you are planning for your timing, you take into account how big your system is; take notes on how long on average it takes to do your harvests, and factor it into your crop timing calculations. This will also inform your decision of what sized sections of your farm you’ll designate for each overlapping crop cycle
Think about your customers – If your market doesn’t want it, don’t grow it. If your market does want it, and you can grow it well, then budget plenty of time and resources to get them what they want when they want it.
Copyright © Partners of the Aqu@teach Project. Aqu@teach is an Erasmus+ Strategic Partnership in Higher Education (2017-2020) led by the University of Greenwich, in collaboration with the Zurich University of Applied Sciences (Switzerland), the Technical University of Madrid (Spain), the University of Ljubljana and the Biotechnical Centre Naklo (Slovenia).