- Match pore behavior to irrigation.
- Compare common media using a practical test.
- Plan preparation, reuse and disposal.
01 / Support and pore space
A growing medium supports roots and stores water in its pore structure. Air-filled porosity after drainage and water held between irrigations both matter. Container height, compaction and particle size change these properties; a material name alone does not define performance.
In NFT, a small plug supports the seedling while most roots grow outside it. In a drip bucket, the medium occupies much of the root volume. In a flood table, it determines the irrigation interval. Choose the medium and irrigation method together.
Reading: Soilless Growing Mediums ↗
02 / Compare the useful tradeoffs
Use this table to form a shortlist, then wet and drain a sample in the actual container. Supplier preparation instructions take priority over a generic soak recipe.
| Medium | Useful property | What to verify | Typical fit |
|---|---|---|---|
| Coir | Moisture retention with manageable container weight | Washing/buffering status, salt content, Ca/Mg interactions, compression | Drip containers; blends. |
| Mineral wool | Uniform manufactured plugs and slabs | Preconditioning, wetting, drainage and handling guidance | Propagation; slab or block irrigation. |
| Expanded clay | Stable coarse structure and reusable physical shape | Fines, grade, buoyancy, water retention and cleaning | Baskets; flood beds. |
| Perlite | Lightweight aerated pore space | Dust handling, grade and outlet screening | Drip buckets; blends. |
| Propagation foam / plugs | Repeatable seedling support | Product composition, disposal and root release | NFT, raft or DWC transplant support. |
| Gravel / aggregate | Weight and durable structure | Carbonate reaction, contaminants, particle size and structural load | Selected media beds after testing. |
Reading: Soilless Growing Mediums ↗
03 / Test before filling the system
Prepare a sample by the manufacturer’s method and capture rinse water so fines do not enter the plumbing. Fill a representative container at the intended density without compacting it arbitrarily. Wet it fully, let it drain, and compare moisture at several depths.
Use a scale if helpful: saturated-and-drained container mass minus its dry mass gives the retained water mass for that test, approximately litres per kilogram of water. That result is not the plant-available fraction, but it helps compare otherwise matched samples.
- Label material, grade, supplier preparation and container dimensions.
- Measure dry container plus medium mass. Wet uniformly and record the method.
- Allow a consistent drainage interval and weigh again. Inspect for dry pockets or standing water.
- Repeat a normal irrigation event and watch how much water moves through versus stays stored.
- Select a medium that supports the intended crop while allowing reliable irrigation, drainage and cleaning.
04 / Reuse is a process
Do not assume a rinsed medium is disease-free. Root fragments and biofilm remain after visible dirt disappears. Reuse suitability depends on material integrity, disease history, cleaning access and a validated sanitation procedure.
Keep seedling propagation separate from dirty media handling. At crop turnover, record whether the medium compacted, broke down or allowed roots to obstruct drains. Include replacement labor and disposal in the operating budget.
FIELD QUESTIONWhy can the same coir behave differently in a tall pot and a shallow tray?
Container geometry changes drainage and the proportion of the root zone that stays wet. The irrigation result belongs to the medium-container combination.
Reading: Clean and disinfect the greenhouse ↗
Parts & buying criteria
Showing ebb and flow. Quantities describe the teaching model. Specify real working volume, support, fittings and instruments for your installation.
01Nutrient reservoir1 · illustrated quantity+
Stores the measured nutrient solution beneath or beside the growing area.
Inspect: Compare the surface with the pump intake or lower roots; freeboard is deliberate.
Maintain: Record level before refilling, keep light out and verify temperature, EC and pH.
Opaque, cleanable, intended-use container with volume marks and service access.
Supplier links can be added by the publisher. The criteria stand independently.02Pump & supply1 · illustrated quantity+
Moves nutrient solution from the reservoir to the growing area.
Inspect: Trace installed lift and branching; the pump label does not prove delivered flow.
Maintain: Measure output after service and inspect intake, filter and minimum water level.
Pump curve matched to installed head, required pressure and service needs.
Supplier links can be added by the publisher. The criteria stand independently.03Growing tray1 · illustrated quantity+
Contains supported media pots above the lower reservoir.
Inspect: Inspect the flood level, pot bases and accessible drain position.
Maintain: Verify full drainage and inspect moisture in representative pots.
Rigid cleanable tray with independent overflow and adequate support.
Supplier links can be added by the publisher. The criteria stand independently.04Root-zone mediumFor illustrated containers · illustrated quantity+
Stores moisture and air around the roots in the illustrated containers.
Inspect: Compare the medium surface with irrigation and drainage.
Maintain: Inspect wetting at several depths; prevent fines from reaching drains and emitters.
Prepared, stable grade matched to the irrigation method and crop.
Supplier links can be added by the publisher. The criteria stand independently.05Drain & overflow1 · illustrated quantity+
Returns drainage to the reservoir and provides a controlled high-water route.
Inspect: Follow the full slope and look for the separate high-level opening.
Maintain: Test pump-off drain-back and keep roots and medium out of the outlet.
Accessible fittings and verified capacity under normal and fault conditions.
Supplier links can be added by the publisher. The criteria stand independently.Evidence beside the lesson.
Source checks: September 2026. The geometry, inspection exercises and worksheets are original teaching material. The named organizations have not endorsed or reviewed this site.
Published recipe rates and planning ranges retain their source context. Calculator equations are accounting tools; they do not predict uptake, yield, toxicity or safe stocking. Model dimensions, water speeds, roots and fish counts are illustrative. Verify species, crop, source water and product labels for a real system.
- Oklahoma State University ExtensionSoilless Growing Mediums ↗
Physical properties and limitations of common growing media.
- NSW Department of Primary IndustriesClean and disinfect the greenhouse ↗
Physical cleaning followed by appropriate disinfection.
The next useful connections.
Ebb and flow: flood, drain, observe
Build a flood table, size its working water inventory and tune irrigation from the medium’s actual wetting and drying.
6 min + guided practice →Growing methodsDrip and Dutch buckets: deliver to every plant
Design a serviceable bucket system for larger crops, then measure irrigation uniformity and drainage.
Interactive tool · 6 min + guided practice →Media & propagationFrom seed to a working root system
Start consistent seedlings, establish root contact and transplant without importing avoidable problems.
6 min + guided practice →