Deep Water Culture and the Water Culture Method for Growing Plants Without Soil

Suspend a plant's roots in water enriched with the right minerals, and it will grow without a grain of soil. That observation, now routine in aquaponics and hydroponic growing rooms around the world, was considered a laboratory curiosity for the better part of three centuries before anyone thought to turn it into a production method. Understanding why it took so long, and what the technique actually demands of the grower, makes it far easier to run a raft or deep water culture system well.

The long pre-history of water culture

The search for how plants feed themselves goes back further than formal science. As documented in The Complete Guide to Soilless Gardening or Hydroponics, investigators were noting that plant cuttings would grow in water long before anyone understood why. Early observers correctly inferred that growth eventually stopped because the plant ran out of food, but they had no idea that nutrients could be dissolved in water or what forms those nutrients took.

The first recorded scientific experiment in this space was conducted by Woodward in 1699, who grew spearmint in rain water, river water, and conduit water, adding garden soil to one batch. As described in Hoagland and Arnon's The Water-Culture Method for Growing Plants Without Soil, Woodward found that the greatest increase in plant weight occurred in water that contained the most soil, and he concluded that earth, not water, was the true substance of vegetation. He was wrong in his conclusion, but his experiment planted a question that took another century and a half to answer properly.

Real water culture, in the sense of deliberately adding dissolved chemicals to support plant growth, dates from 1860. According to The Complete Guide to Soilless Gardening or Hydroponics, it was Knop, a German agricultural chemist, and Sachs, a botanist, who first added chemicals to water and obtained working nutrient solutions. Knop's primary interest was in understanding the relationship between soil and crop production; Sachs was more interested in plant processes and botany. In the end it was Sachs' perspective that dominated the field. The result, as the same source notes, was that scientific literature from 1860 to 1929 contains no suggestion that water culture principles might ever be applied to practical crop production. Researchers used these techniques to study plants, not to grow food.

By 1842, a list of nine elements believed essential to plant growth had been compiled, and as documented in Hydroponics: The Bengal System, the experiments of Sachs and Knop between 1859 and 1865 developed the technique of soilless cultivation to a point where, by 1920, laboratory preparation of water cultures had been standardised. The methods were well established. Still, no one had tried to use them outside the laboratory.

How hydroponics entered the world of practical horticulture

The moment that changed everything came in 1929. According to Hydroponics: The Bengal System, Professor W. F. Gericke of the University of California succeeded in growing tomato vines twenty-five feet in height using a nutrient solution, and even sceptical observers were astonished. Gericke named his discovery "hydroponics," from Greek roots meaning water-working. The American press responded with what the same source describes as "magnificent abandon," announcing that farmland had become a relic of the past, with photographs of Gericke harvesting his crop from a stepladder circulating widely.

The enthusiasm was excessive. As Hoagland and Arnon document, promoters made wholly unfounded claims that a new profession of soilless farming had been developed, offering extraordinary opportunities for investment. Sunday newspaper supplements ran illustrations of housewives picking tomatoes from vines growing in water culture in kitchen closets under electric lights. Rumours circulated that restaurant chains in New York were growing their vegetables in basements. Hoagland and Arnon were unsparing in their assessment: most of these claims, they wrote, betrayed an ignorance of even the elementary principles of plant physiology.

The sober reality, as summarised in the California Agricultural Experiment Station circular by Hoagland and Arnon, is that nutriculture is rarely superior to soil culture under comparable conditions. Yields are not strikingly different. Plants cannot be spaced more closely than in a rich soil. Water requirements are no less. Climatic requirements are identical. Nutrient deficiencies, insect attacks, and diseases present similar problems. The method has real value, but it is not magic.

Gericke had grown his first plants in large basins of nutrient solution. As Hydroponics: The Bengal System records, the technique subsequently spread and adapted: sand and gravel culture was developed in the Middle West of the United States to suit different regional conditions, and over the following decade several practicable systems of soilless culture emerged from research institutions including the Universities of Illinois, Ohio, Purdue, and California, as well as the University of Reading in Great Britain and Canada's Central Experimental Farm at Ottawa.

What water culture actually is

Strip away the historical drama and water culture is a straightforward concept. As described by Agriculture Canada's publication Soilless Growth or Hydroponics, the method consists essentially of supporting plants with their roots dipping into a tank or container of nutrient solution. The solution dissolves and delivers the eleven elements essential to plant growth: nitrogen, potassium, phosphorus, calcium, magnesium, sulphur, iron, manganese, boron, zinc, and copper, as listed in The Complete Guide to Soilless Gardening or Hydroponics. These exist in simple chemical combinations that can be dissolved in water and delivered directly to the root zone.

The containers themselves can be made of wood, glass, concrete, or metal. Individual plants can be supported by baskets of ungalvanised wire screen hooked onto the rim, with the plant held in the basket by a few centimetres of excelsior, straw, or other low-nutrient material. In smaller glass containers, a cork or piece of wood resting on the rim, with a hole for the stem and cotton wrapped around the stem at that point, will do the job. The key requirement, as Agriculture Canada's publication notes, is that the tank be kept dark to prevent algae growth.

The nutrient solution itself needs to be maintained at a temperature favourable to root growth. Agriculture Canada recommends 21 to 27 degrees Celsius, achievable with an immersion heater regulated by a thermostat where necessary.

The oxygen problem and why it matters

The single most important practical challenge in water culture is aeration. Roots need oxygen, and a root system permanently submerged in still water will eventually suffocate. As Agriculture Canada's Soilless Growth or Hydroponics explains, aeration is not easily accomplished in water culture because the roots are constantly immersed and it is difficult to make water absorb air.

Several approaches address this. In small individual containers, simply propping the plant so that the root mass does not touch the bottom of the vessel can allow some air exchange. In larger tanks, the options include agitating the solution vigorously, circulating it by pumping it up into a tower and letting it fall by gravity over a grating, or forcing air directly into the solution with a pump. The last approach, using an air pump and airstone, is the one most familiar to modern growers of deep water culture systems. In aquaponics, the fish tank pump and the biological activity of the system add further aeration to the water before it reaches the plant roots.

Hydroponics: The Basics describes a related system called Deep Flow Technique (DFT), in which a trough much like a nutrient film channel runs with roots submerged by roughly forty percent of the gully height for around fifteen minutes, then drains down to just a millimetre of depth for the next fifteen. The design is intended to ensure that the nutrient solution never stagnates, roots are never flooded long enough to drown, and the system is heavily aerated throughout. The same source notes that DFT has produced excellent results for some growers and less impressive results for others, with the difference often coming down to adherence to the basic rules: correct light, adequate oxygen, appropriate nutrient strength, correct pH, and suitable temperature.

The raft idea has older roots than most people know

The floating raft approach to water culture, in which plants sit on a buoyant platform above a body of nutrient-rich water, is usually associated with modern commercial aquaponics. But Hydroponics: The Bengal System points out that something very like it has been practised for centuries. Visitors to Kashmir have observed light frameworks of branches covered with decomposed vegetation floating on lakes, from which local farmers raise excellent crops. The rafts provide both water and nutrients to the growing plants. A similar tradition of floating gardens was used by the Aztecs of Mexico before the Spanish conquest in the sixteenth century.

These historical examples are not true hydroponics in the technical sense, since the nutrient source is decomposed organic matter rather than a prepared chemical solution. But they demonstrate the same underlying principle: roots in contact with nutrient-bearing water, supported above it, can sustain vigorous plant growth. The modern raft system used in aquaponics formalises and refines that observation. Plants sit in net pots set into a floating polystyrene sheet, with roots hanging into water that the fish have fertilised and beneficial bacteria have converted into plant-available nutrients.

What the technique demands of the grower

Hoagland and Arnon were emphatic that anyone who uses water culture must have a working knowledge of plant physiology. This is not false modesty. The soil in a garden is a vast and forgiving buffer: it holds nutrients, moderates pH, supports microbial communities, and corrects for many grower errors over time. A water culture system has none of that inbuilt resilience. When something is wrong with the solution, the roots feel it immediately.

The Complete Guide to Soilless Gardening or Hydroponics puts it this way: the evolution of water culture into hydroponics has been the story of using ordinary materials to reproduce the conditions that soil naturally provides. The soil is a reservoir of water, so a basin is needed. The soil provides eleven food elements in solution, so these must be added to the water. The soil anchors roots and positions plants relative to the nutrient solution, so a seedbed or support structure must do that work instead. Every function that soil performs automatically must be replicated deliberately.

The same source observes that the outstanding lesson of early hydroponic experiments was that understanding plants, their adaptability to varying conditions, and their individual differences matters more to success than the ability to handle equipment or prepare the right nutrient mix. That observation applies equally to a raft system in a backyard aquaponics setup. The plants will tell you what they need, but only if you know what to look for.

Annual plants grown from seed are the easiest starting point in any water culture system, as The Complete Guide to Soilless Gardening or Hydroponics notes. Leafy greens, herbs, and fast-growing annuals suit the method well. The more complex the plant's life cycle, the more specialised the technique required to support it.

Why water culture persists despite its demands

Given the qualifications and the care required, it is reasonable to ask why water culture remains so widely used. The answer is not that it produces dramatically higher yields, because as Hoagland and Arnon documented, it generally does not. The answer is that it gives the grower precise control over what the root zone receives, it eliminates many soil-borne pathogens and weed competition, and in certain specific conditions, particularly where good soil is unavailable or where water efficiency matters, it offers genuine practical advantages.

In aquaponics, the attraction of the raft system is partly structural. A large shallow tank of fish-fertilised water is already present, and floating plants across it is a clean and scalable way to use that resource. The fish supply nitrogen continuously; bacteria convert it to nitrate; the plants absorb it and clean the water in the process. The water culture method slots naturally into that cycle. Research from the University of the Virgin Islands into raft aquaponics has explored how this relationship can be optimised at scale, and those findings continue to inform how hobbyists and small commercial operators design their systems.

What has not changed since Hoagland and Arnon wrote their circular in 1950 is the basic requirement: a grower who understands what their plants need, watches the system closely, and responds to what they see. The technique is neither magical nor impossibly difficult. It is simply a method that rewards attention and punishes inattention rather more quickly than soil does.