Grow

Hydroponics or soil: which is right for a smallholding

Both systems grow food. Only one of them survives a stage 6 blackout without a backup plan. Here is what the comparison actually looks like in South Africa.

David Watts · Filed under Grow

How the two systems actually differ

The surface comparison is straightforward: hydroponics grows plants in a nutrient solution without soil; soil growing does the opposite. The practical comparison is more interesting. The two systems have different failure modes, different skill requirements, and different relationships with the two resources that are least reliable in South Africa — water and electricity.

This article is not about which system is better in the abstract. It is about which one is right for a specific situation, and it is honest about the fact that for some situations the answer is neither yet.

Water use, honestly compared

Hydroponics is consistently cited as using 70–90% less water than conventional soil growing. The figure comes from recirculating systems — nutrient film technique (NFT), deep water culture (DWC), and flood-and-drain — where the solution is recovered and reused rather than lost to the ground. The Food and Agriculture Organisation of the United Nations puts typical water savings in controlled hydroponic systems at around 70% compared to field production for equivalent yield (FAO, 2018).

That saving is real. It is also conditional. It assumes a recirculating system that is correctly designed, correctly maintained, and not leaking. An NFT channel with a blocked return line or a reservoir that is not topped up correctly wastes water faster than a drip-irrigated bed. The saving exists when the system is working as intended.

Soil systems, particularly unirrigated or drip-irrigated raised beds with good mulch cover, are more water-efficient than the comparison usually allows. Open furrow irrigation on flat ground in full sun is genuinely wasteful. A mulched raised bed with a sub-surface drip line is not the same thing, and most smallholder comparisons conflate them.

The honest position: a well-run hydroponic system uses significantly less water than a poorly managed soil system, and roughly the same as a well-managed drip-irrigated bed with good organic matter. Water saving alone is not a sufficient reason to choose hydroponics over soil.

Method	Typical water use (litres/kg of leafy greens)	Key variable
Open furrow, bare soil	250–400	Evaporation, soil type
Raised bed, mulched, drip-fed	80–150	Mulch depth, organic matter
Flood-and-drain hydroponics	20–60	Recirculation efficiency
NFT hydroponics	15–50	System integrity, no leaks
Deep water culture	20–70	Reservoir management
F	i	g	u	r	e	s		a	r	e		i	n	d	i	c	a	t	i	v	e		r	a	n	g	e	s		f	r	o	m		F	A	O		a	n	d		p	u	b	l	i	s	h	e	d		a	g	r	o	n	o	m	i	c		l	i	t	e	r	a	t	u	r	e	.		A	c	t	u	a	l		u	s	e		v	a	r	i	e	s		w	i	t	h		c	r	o	p	,		c	l	i	m	a	t	e	,		a	n	d		o	p	e	r	a	t	o	r		s	k	i	l	l	.

Why hydroponics is different in South Africa

The load-shedding failure mode

This deserves its own section because it is the most common reason hydroponic systems fail in South Africa and the least discussed in the literature that promotes them.

NFT systems are the most vulnerable. The film of nutrient solution across the growing channels is thin by design — roots are never submerged, they sit in a flowing film with air above. When the pump stops, the film stops. In temperatures above 25°C, wilting begins within two to three hours. At 35°C — a normal Highveld summer afternoon — the window is shorter.

Deep water culture is more tolerant because roots are submerged in a reservoir. But the air pump aerating that reservoir also stops during load-shedding. Without oxygenation, root rot begins within 24–36 hours in warm water. DWC buys more time than NFT, but not enough to ride out a full load-shedding cycle without intervention.

Flood-and-drain systems are somewhere between the two. The growing medium retains some moisture after a flood cycle, and the plants have more time before stress becomes damage. They are still not safe across a 6-hour outage in summer.

The solution is straightforward: a dedicated circuit on an inverter or UPS sized to run the system's pumps continuously. The complexity is that this requires knowing the system's power draw before specifying the backup, and it requires the backup to be in place before the first crop goes in, not after the first crop is lost. See how much solar you actually need for guidance on sizing a backup circuit.

Skill, time and attention required

Soil growing has a long tolerance gradient. A beginner who makes mistakes with spacing, watering, or fertilising will get a reduced harvest, not necessarily no harvest. The system absorbs errors. Beneficial soil organisms buffer pH swings, organic matter holds nutrients through erratic watering, and most soil-grown crops will recover from short periods of neglect.

Hydroponics has a shorter tolerance gradient, particularly for beginners. The nutrient solution requires regular pH and EC (electrical conductivity) monitoring. pH outside the 5.5–6.5 range locks out specific nutrients regardless of how much of them is in the solution. EC that drifts too high causes salt stress; too low causes deficiency. Both manifest as leaf symptoms that are easy to misread without experience.

This is not an argument against hydroponics for beginners. It is an argument for beginning with a forgiving system — DWC with a large reservoir buffer, for example — and building the monitoring habit before scaling. The monitoring itself is not difficult. It requires a pH meter, an EC meter, and a check every one to two days. The difficulty is building the discipline before something goes wrong, not after.

Time commitment is similar for both systems at small scale, and higher for hydroponics at larger scale. A soil bed requires watering, weeding, and occasional feeding. A hydroponic system requires daily checks, reservoir top-ups, and periodic full solution changes. Weeding is eliminated, but it is replaced by monitoring.

Which crops suit which method

Hydroponics performs best with fast-growing, shallow-rooted crops that respond to optimised nutrition: leafy greens (lettuce, spinach, pak choi, Swiss chard), herbs (basil, coriander, mint), and some fruiting crops (cherry tomatoes, cucumbers, peppers) in larger systems. The economic logic of hydroponics — high yield per square metre, fast turnover — applies most clearly to these crops. See microgreens for the most space-efficient version of this logic.

Root vegetables are not suited to most hydroponic systems. Carrots, beetroot, and potatoes need a growing medium with structural depth and will not perform well in NFT or DWC without significant system modification. They are soil crops.

Fruit trees, perennial vegetables, and deep-rooted crops are not hydroponic candidates at smallholding scale. These are soil crops by definition.

The practical implication: a smallholding that wants to grow most of its own food across a full variety of crops needs soil. Hydroponics can contribute high-value, fast-turnover leafy greens to that mix, but it cannot replace the soil component.

Crop type	Soil	Hydroponics	Notes
Leafy greens (lettuce, spinach)	Good	Excellent	Hydroponic speed and yield advantage is largest here
Herbs (basil, coriander)	Good	Excellent	Basil particularly responsive to hydroponic conditions
Cherry tomatoes, cucumbers	Good	Good	Hydroponics needs a larger, more complex system
Root vegetables (carrot, beetroot)	Good	Poor	Structural depth required; not suited to NFT or DWC
Brassicas (broccoli, kale)	Good	Moderate	Space per plant reduces the yield advantage
Beans, peas	Good	Moderate	Support structures required; soil easier
Fruit trees, perennials	Good	Not viable	Soil only at smallholding scale
Sweet corn	Good	Not viable	Space and root requirements make it impractical

What people get wrong

The most common mistake is treating hydroponics as a replacement for soil rather than a supplement to it. A smallholder who converts all available growing space to hydroponic channels and then experiences a 4-day power outage with an undersized inverter loses everything. The same smallholder with half the space in soil beds and half in hydroponics loses the hydroponic crop and retains the soil crop.

The second mistake is building a system before testing the water source. Municipal water in South Africa varies significantly in pH and mineral content between municipalities — and within the same municipality across seasons as the source changes. Borehole water is more variable still, and some borehole water is too high in iron, manganese, or total dissolved solids to use in a recirculating hydroponic system without treatment. The nutrient solution builds on whatever is already in the water, and starting from a known baseline matters. Test the source water before building the system, not after the first nutrient lockout.

The third mistake is underestimating the reservoir management requirement in South African heat. A 100-litre reservoir sitting in a shadehouse on a 38°C day in Limpopo will reach temperatures that favour root pathogens and reduce dissolved oxygen. This is not a northern-hemisphere problem in the same way, and northern-hemisphere guidance on reservoir sizing and management does not always account for it.

Who each one is actually for

Soil is for: anyone starting out, anyone without reliable backup power, anyone who wants to grow the full range of crops a smallholding produces, anyone whose water source has not been tested and whose pH is unknown. Soil is also for anyone whose primary goal is food security rather than yield optimisation — the failure modes are slower and more recoverable.

Hydroponics is for: growers who already have stable backup power and have tested it under real load-shedding, who want to maximise yield from a small footprint, who are focused on fast-turnover leafy greens and herbs, and who are prepared to monitor the system daily. It makes particularly strong sense where water is genuinely scarce and the source is known and suitable. It also makes sense as a commercial supplement — a hydroponic bay of lettuce can generate consistent, high-value produce to sell or supply to a restaurant while the rest of the smallholding produces a broader food mix from soil.

The framing of "which is better" is the wrong question. The right question is "what do I have stable enough to support each system?" If the answer is "I have reliable backup power and a known water source", hydroponics is a legitimate option. If the answer is "I am still on Eskom with no backup", the load-shedding failure mode makes hydroponics a high-risk choice regardless of its other advantages.

What we would do differently

• Establish soil beds first and get one full season of production before considering any hydroponic investment. Soil gives you food while you learn.
• Test the water source before designing a hydroponic system — pH, EC, iron, and total dissolved solids at minimum. A basic water test kit costs little and changes the system design.
• Size the backup power for the hydroponic pumps specifically, and run a full load-shedding simulation before the first crop goes in. Do not assume the inverter will cope; measure the actual draw.
• Start with deep water culture rather than NFT if power reliability is uncertain. The larger reservoir buffer buys time during an outage that NFT does not.
• Keep the hydroponic footprint smaller than the soil footprint until the power and monitoring systems have been tested through at least one summer.
• Use the hydroponic system for the crops where it has the clearest advantage — leafy greens and herbs — and grow everything else in soil.
• If water is from a borehole, re-test it at the start of each season. Borehole chemistry can shift with water table changes.

Is it worth it?

Hydroponics is worth it when the conditions for it are genuinely in place: backup power, known water source, daily monitoring, and a crop focus that suits the method. Under those conditions, the yield per square metre and the water efficiency are real advantages, not marketing claims.

It is not worth it as a first system, as a replacement for soil, or as something to set up and check weekly. The failure modes are fast and they compound — a pH crash that goes unnoticed for three days is a dead crop, not a sick one.

The honest position for most smallholdings in South Africa at the moment is: soil first, hydroponics later. Not because hydroponics is inferior, but because the infrastructure it depends on — reliable power or robust backup — is not yet a given, and the sensible sequence is to secure food production before optimising it.