A hydroponic grow makes an unusually good school business project because the whole cycle fits inside one term. In roughly six to eight weeks a class can move from seedling to a stall of fresh greens sold at a market day or year-end fair. This guide walks through that cycle as a real small business: choosing crops that finish in time, costing the inputs, setting a defensible price, selling on the day, and getting the most learning out of the batch that flops.

Why a hydroponic grow works as a business project

Most classroom businesses are simulations. A hydroponic grow is not. Real water, real nutrients, real electricity and real plants turn into produce that real people pay for. The cycle is short enough to finish inside a term, the footprint is small enough for a corner of a classroom, and every input is measurable. That last point is what makes it teachable. Seeds, medium, nutrient solution and power all have a cost, so students end the term holding a profit-and-loss sheet they built themselves. It sits naturally alongside the maths, science and coding they already do in a coding and robotics programme.

Pick crops that finish inside a term

The six-to-eight-week window is the hard constraint. It rules out fruiting crops. Tomatoes, peppers and strawberries take months and will still be flowering on market day. Go leafy and fast instead, and sow the whole class in the same week so the harvest lands together.

• Loose-leaf lettuce: forgiving, quick, sells by the bag.
• Rocket and mustard greens: fast and peppery, popular with parents.
• Basil, coriander and mint: herbs fetch more per gram than lettuce.
• Spinach and pak choi: reliable and familiar to buyers.

A note on timing. Sowing in September for a November sale puts your harvest in late spring, when heat and longer days push leafy crops to bolt, meaning they run to seed and turn bitter. Choose heat-tolerant varieties, keep the water cool, and harvest a little early rather than a little late.

Cost it like a real business

Split your costs into two piles. One-off setup is spent once and reused every cycle: reservoir, pump, net cups, medium holders, and either grow lights or a sunny north-facing window. Per-cycle consumables are spent every batch: seeds, growing medium, nutrient solution and electricity. Only the second pile belongs in the price of this term's greens. The setup is capital.

Two South African realities belong in the budget. First, electricity for a small pump is cheap but not free, so meter it. Second, load shedding will stop a pump for hours, and a stalled pump in warm weather can cost you the whole crop. Either add a small battery backup, or run a passive Kratky-style setup that needs no pump at all. Students who want the automation challenge can put the pump on a timer and log the water level with a microcontroller such as the sheenbot∞ board, which turns the grow into a coding project as well as a business one.

• Seeds: a rand or two per plant, often less in bulk.
• Growing medium: coco coir, rockwool or clay pebbles, part of it reusable.
• Nutrient solution: the biggest recurring cost, so measure it rather than eyeball it.
• Electricity: small, but real, and worth noting so the P&L is honest.

Set a price that covers cost and reality

Start with cost-plus. Add up the per-cycle consumables, divide by the number of plants you actually expect to sell rather than the number you sowed, since some will fail, and that is your unit cost. Add a margin on top. Then sanity-check against the shop: what does a bag of salad leaves or a bunch of herbs cost at the supermarket down the road? Price near or a little under that, and lean on your one real advantage, which is that your greens were cut the same morning. Selling by the bag or the bunch is easier than selling by weight, and taking pre-orders from parents the week before cuts waste and guarantees some income.

Sell it on market day

Term four is full of fairs and market days, so the calendar is on your side. Treat the stall as part of the product.

1. Harvest the morning of the event, and keep the greens cool and lightly misted.
2. Bag or bunch them cleanly, with a simple label naming the crop and the class that grew it.
3. Put the rig on the table. The pump, the pH pen and the logbook draw people in, and the story sells as much as the produce.
4. Keep a float for change and, if you can, a way to take card or instant EFT.

When the crop flops, and it might

Some of the batch will fail, and one term the whole thing might. Root rot, algae in a clear reservoir, pH drift, aphids, nutrient burn, or a pump that died during load shedding are all normal failures with normal causes. A flop is not a failed project. It is the data. Sit the class down and work it as an investigation: what changed, what did we measure, and what is the single variable we would control next time. That loop of hypothesis, failure and iteration is the actual curriculum. The greens were only ever the excuse to run it.

The takeaway

The produce is the by-product. What students keep is a costing they built, a price they defended to a real customer, and, in the best years, a failure they diagnosed and fixed. That is a stronger business lesson than any simulation, and it fits inside a single term. If you want help running one, our holiday workshops are a good place for a class to build the automation and the grow together, and there is more on project-based STEM in the newsroom.

What is the cheapest way to start?

A passive Kratky setup in a bucket or storage tub. No pump, no electricity, and no load-shedding risk. It grows leafy greens well and is the safest first cycle for a class on a tight budget.

How many plants should a class stall grow?

A rig of twenty to forty net cups is plenty for a first market day. It yields enough to sell without overwhelming students at the harvest and packing stage, and it keeps the nutrient and setup cost modest.