How trays shape watering, airflow, hygiene, and repeatable results as you scale
Microgreen trays don’t usually get much attention, but they shape almost everything about how a microgreens system behaves. Trays determine how water moves, how air reaches the root zone, how easy cleaning is, and how repeatable your results are across racks, rooms, and seasons.
When trays are chosen well, watering becomes predictable, germination evens out, hygiene is easier to maintain, and scaling up feels manageable. When trays are poorly chosen, small problems stack up quickly and become hard to untangle.
This guide isn’t about finding the “perfect” tray. It’s about understanding what trays actually do in a working system, so you can choose something that supports consistency rather than fighting it.
Direct answer: most tray-based systems converge on a simple standard: a grow tray with holes sitting inside a reservoir tray with no holes, plus a blackout or cover tray for germination. Standardise your tray footprint early (1020 or 1122), choose rigid, food-contact plastic, and favour shallow grow trays unless you have a clear reason not to.
Tray Selection Checklist (the decisions that remove friction later)
- Pick one footprint and commit: 1020 or 1122, then build racks, lights, and workflows around it
- Use the three-tray method: grow tray (holes), reservoir tray (no holes), blackout/cover tray
- Choose shallow grow trays by default: better airflow, drying behaviour, and harvest ergonomics
- Prioritise rigidity over price: flat trays water evenly and behave on flood tables and racks
- Use food-contact plastics: PP or HDPE, sold for food growing, BPA-free, easy to sanitise
- Separate growing trays from sales containers: live punnets are a sales format, not just a small tray
Quiet red flags: thin flexible trays that warp, inconsistent tray sizes on the same rack, hole patterns that flood or wick unevenly, and tray systems that force top watering because bottom watering is awkward.
The Three-Tray Method (and why most systems converge on it)
Most tray-based microgreens systems eventually converge on what’s often called the three-tray method, even if the individual components vary. It’s become standard because it’s simple, repeatable, and adaptable across many media types.
1) The grow tray (with drainage holes)
The first role is the grow tray, the tray with drainage holes. This tray holds the growing medium. The holes allow roots to access water from below while letting excess drain away, keeping the root zone oxygenated instead of sitting in stagnant water.
Hole size and spacing matter more than people expect. Good patterns support even wicking without flooding the tray.
2) The reservoir tray (with no holes)
Underneath sits the reservoir tray, the tray with no holes. This holds water for bottom watering. Bottom watering keeps foliage dry, reduces splash, and significantly lowers mould pressure compared to top watering.
It also produces more even hydration across the tray, especially once systems scale.
3) The blackout or cover tray
The third role is the blackout or cover tray. This is used during germination to maintain darkness and humidity until roots establish. Some growers stack trays. Others use dedicated blackout covers.
The exact method matters less than the outcome: stable moisture and darkness early on.
Tray Size: 1020 vs 1122 (why consistency matters more than the number)
Tray size becomes more important as systems grow. In the UK and much of Europe, the common standard is the 1122 footprint. In the USA and many other regions, it’s the 1020.
Neither is inherently better, but consistency matters enormously. Racks, lights, flood tables, and workflows are usually built around one size. Mixing tray sizes complicates lighting layouts, watering, storage, and future expansion.
Choosing a standard early and sticking with it removes a surprising amount of friction later.
Tray Depth: Why Shallow Trays Dominate Commercial Systems
Tray depth is another area where misunderstandings creep in. In microgreens, depth is not about growing bigger plants. It’s about airflow, drying behaviour, humidity control, and ease of handling.
This is why shallow grow trays dominate commercial systems.
What shallow grow trays improve in practice
Shallow trays improve airflow across the media surface, dry more predictably after watering, reduce humidity trapped around stems, make harvesting easier, and reduce both media use and saturated weight.
They integrate well with racks and automated watering and work across compost, coir, mat, and fibre systems.
When deeper trays can make sense
Deeper grow trays do have niche uses. They can help in very warm, dry environments where shallow trays dry too quickly, or where thicker media layers are deliberately used for moisture buffering. Some heavier-built trays also gain rigidity from extra depth.
Outside of those cases, deeper trays usually introduce more problems than they solve.
Why deeper trays often create problems in production
In most commercial or semi-commercial setups, deeper trays increase media costs per tray, add significant saturated weight, slow drying after watering, trap humidity near the crop surface, reduce airflow, raise damping-off and mould pressure, and make harvesting slower and more awkward.
In practice, deeper trays are far more common in hobby setups, where labour efficiency and tight environmental control matter less. For repeatable systems, shallow trays almost always perform better.
Scaling Up: When Flood-and-Drain Tables Start to Win
As systems scale, filling individual reservoir trays becomes labour-heavy and inconsistent. This is where flood-and-drain (ebb-and-flow) tables come in.
Instead of dozens of small reservoirs, multiple grow trays sit directly on a table that floods to a set height and then drains back to a central tank. The principle remains bottom watering. What changes is scale, repeatability, and labour efficiency.
Flood tables work best when the system is designed around them from the start. Adding them as an afterthought often exposes weaknesses elsewhere.
Why tray quality matters more on flood tables
When using flood-and-drain tables, tray quality matters more. Tables reveal issues that individual reservoirs can hide. Trays must sit completely flat, resist warping, and have hole patterns that allow fast, even wicking during short flood cycles.
Shallow grow trays generally perform better here because they wick quickly, don’t require long floods, and drain and re-oxygenate efficiently. At this stage, standardised tray footprints become critical, as tables are built for efficient packing rather than flexibility.
Group crops by water demand
When running flood tables, grouping crops by water demand becomes extremely important. Ideally, run one crop type per table, or group crops with very similar needs.
Heavy drinkers should not share tables with low-water crops. Flood tables reward uniformity and punish compromise. Mixing water demands on a single table almost always leads to under- or over-watered trays.
Tray Materials: Food Safety, Warping, and Real-World Durability
Because microgreens are grown wet and eaten raw, tray material matters. Food-contact-appropriate plastics such as polypropylene (PP) and HDPE are the norm. Trays should be explicitly sold for food growing or food contact, BPA-free, and rigid enough to resist warping under repeated cleaning.
Thin, flexible trays may be cheaper upfront, but they warp, leak, and create uneven watering over time.
Colour and rigidity are functional, not aesthetic
Colour and rigidity matter more than aesthetics. Dark, opaque trays reduce light reaching standing water and help limit algae growth.
More importantly, rigid trays sit flat on racks and tables, distribute water evenly, tolerate repeated sanitising, and reduce breakage and spills. In real production environments, upgrading tray rigidity is often one of the highest-impact improvements a grower can make.
Growing Trays vs Sales Containers (live punnets are a different system)
It’s worth separating trays used for growing from containers used for selling. Punnets for live microgreens are not just small trays. They’re a sales format.
When selling live product, the container stays with the crop, cleanliness becomes critical, and the substrate must anchor roots securely. This is why fibre-based systems pair naturally with punnets. In those cases, tray choice, substrate, and sales model are all part of one integrated system.
Choosing Trays Without Overthinking It
Choosing trays doesn’t need to be complicated if you start with the right questions:
- How will you water, individual reservoirs or flood tables?
- How strict are your hygiene requirements?
- How consistent do results need to be?
- Are you selling cut greens or live product?
Once those answers are clear, tray selection becomes a straightforward match between workflow and hardware.
Trays aren’t glamorous, but they’re foundational. When they’re right, the rest of the system gets quieter, calmer, and far more predictable.
FAQ
What trays are best for microgreens?
Rigid, food-contact plastic trays in a standard footprint (1020 or 1122), using a grow tray with holes inside a reservoir tray. Shallow grow trays are usually the best default because they dry and wick predictably and are easier to work with at scale.
What is the three-tray method for microgreens?
A grow tray with drainage holes holds the medium, a reservoir tray with no holes holds water for bottom watering, and a blackout or cover tray supports stable darkness and humidity during germination.
Are shallow or deep trays better for microgreens?
Shallow trays are usually better for repeatable systems because they improve airflow, dry more predictably, reduce humidity trapped around stems, and reduce saturated weight. Deep trays have niche uses in hot, dry environments or when deliberately using thicker media for buffering.
When should I move to flood-and-drain tables?
When filling individual reservoir trays becomes labour-heavy or inconsistent. Flood tables improve repeatability and reduce labour, but they demand flatter, more rigid trays and better crop grouping by water demand.
What tray materials are food safe for microgreens?
Food-contact plastics like polypropylene (PP) and HDPE are common. Choose trays explicitly sold for food growing or food contact, BPA-free, and rigid enough to resist warping under repeated washing and sanitising.