How to Grow Microgreens in a Sprouting Tray: Soil, Coco Coir & Reusable Medium Guide

March 18, 2026

If you've watched our YouTube channel before, you may have seen us using some trays that are a little different from the typical 10x20 trays. So what are they?

Technically, they're called "sprouting trays," and they weren't originally designed for growing microgreens at all. They're meant for sprouting, which is a completely different growing method. But over the years, we've figured out how to use them really well for microgreens, and at this point they've become one of our favorites.

In this blog, we're going to walk you through exactly how to grow microgreens in a large sprouting tray using three different grow mediums: soil, coco coir, and our reusable silicone grow medium. We'll cover tray specs, seeding rates, watering tips, and the specific quirks that make these trays a little different from what you may be used to.

Brand new to growing? Pair this blog with our beginner's guide to growing microgreens for the full foundation.

Quick Answer: How Do You Grow Microgreens in a Sprouting Tray?

To grow microgreens in a large sprouting tray, place the white mesh tray on top of the green solid tray, fill the mesh tray about ¾ full with soil or coco coir (or drop in a reusable silicone grow medium sized for the tray), seed evenly, water in, then cover with the green tray and add weight for germination. After 2 to 4 days, blackout for 1 to 2 days, then move to light and switch to bottom watering with 2 to 2½ cups of water. Most crops harvest in 7 to 14 days.

Why Use Sprouting Trays for Microgreens?

There are two big reasons people reach for these trays: cost and space.

Sprouting trays are generally more affordable than standard 10x20 trays, which makes them a great option if you want to grow more without spending a lot upfront. And because they're smaller, they're easier to fit into tight spaces, a shelf, a countertop, or a small grow tent.

Don't let the size fool you though. We've consistently pulled solid harvest weights from these trays, especially once you dial in your watering. The benefits absolutely outweigh the challenges in our experience.

A quick heads up on sourcing: On The Grow no longer sells the sprouting tray sets themselves. They're widely available from other retailers, and the ones we recommend are in our Amazon sprouting tray list. We do still sell the reusable silicone grow mediums sized for these trays, in both the large sprouting tray and small sprouting tray sizes, so if you already own sprouting trays or pick up a set elsewhere, you can pair them with a medium that lasts for cycles instead of buying soil every grow. If you're shopping for trays from scratch and want our current in-house recommendation, take a look at our 7x14 OTG Microgreen Tray Kit or our 10x20 Trays & Flats.

Tray Specs: Know What You're Working With

Before you get started, it helps to know what you're actually dealing with. A Large Sprouting Tray Set includes a white mesh tray and a green solid tray that work together throughout the entire grow.

Tray dimensions:

External tray size: 12.75" × 9.5" × 1.875"
Mesh tray internal size: 11" × 8" × 1"
Green tray internal size: 11" × 8" × 1.5"
Mesh hole size: 2.5 mm
Soil/coco coir capacity: approximately 3 to 4 cups

The white mesh tray holds your grow medium and seeds. The green solid tray acts as your bottom-watering reservoir once you move to light, and flips upside down to serve as your blackout dome earlier in the grow. The 2.5 mm mesh holes are large enough to grow bigger seeds like peas, wheatgrass, and mung beans directly on the tray without any medium at all, and a reusable silicone grow medium covers smaller seeds like broccoli that need a finer surface.

One thing worth knowing upfront: the green tray has a small notch in it, which means it doesn't create a fully sealed environment when using it as a lid. That's fine, just don't rely on it alone to retain humidity. Watering twice daily during germination is what keeps moisture where it needs to be, and making sure there are no fans pointed directly at the trays during germination.

Choosing Your Grow Medium

One of the first decisions you'll make is which grow medium to use. Here's a quick overview of each option before we get into the step-by-step:

Soil: Great for beginners. It's forgiving, retains moisture well, and most varieties do well in it. Use a seed-starting mix and fill the mesh tray about ¾ full (roughly 3 cups). Most quality soil mixes already carry the nutrients a microgreen crop needs, so we don't suggest adding liquid fertilizer on top.

Coco Coir: Similar to soil in how it's used, but it's a more neutral medium with no nutrients on its own. The big advantage is that you can add hydroponic nutrients when you switch to bottom watering, which can give your crop a boost. Also a great choice if you want a cleaner, less earthy setup. We no longer carry coco coir, but the one we use is available through our Amazon affiliate link.

Reusable Silicone Grow Medium: Our sprouting tray-sized silicone medium is sized at the factory to 8" x 10" and drops right into the white mesh tray, with a small sprouting tray size available too. No soil, no mess, just rinse, reuse, and grow again. It works great for most varieties and is especially popular with folks who want a long-term, sustainable setup. We'll cover this option in its own section below.

Lush microgreens growing in white mesh sprouting trays at full canopy

Step-by-Step: Growing with Soil or Coco Coir

Step 1, Prep your tray

Place the white mesh tray on top of the green solid tray. Fill the mesh tray with soil or coco coir until it's about ¾ full, approximately 3 cups. Break apart any clumps and remove any large twigs if present (microgreens don't like growing on sticks). Spread the medium evenly across the tray and lightly tamp it down with your hands. Don't pack it tight, just a gentle press to level it out.

Adding grow medium to a sprouting tray for microgreens

Step 2, Choose your seeds and measure

Not sure where to start? We suggest beginner-friendly varieties like broccoli, kale, collard, radish, peas, and beans for your first few grows. If you want a wider look at what's out there, our overview of how many types of microgreens there are covers the full range. You can get all of these through our affiliate partner True Leaf Market.

For seeding amounts, the large sprouting tray is roughly half the size of a standard 10x20 tray, so use about half the amount you would for a 10x20. Here are some general starting points:

Broccoli, kale, radish, and other small seeds: ~10 to 20 grams
Sunflower: ~65 grams (no soak needed, always rinse before planting to remove hull debris)
Peas: ~120 grams

You can also reference our free Tray-Specific Seeding Guide PDF for variety-by-variety seeding rates adjusted for sprouting tray sizes.

Halving a 10x20 rate works, but it's a rough estimate, and it gets messier the moment you're also running 10x10s or 7x14s on the same shelf. That's one of the reasons we built Microgreen Tracker, our grow-tracking web app. Seed amounts are stored as a density instead of a fixed gram number, so you set your rate once for a crop and the app calculates the seed weight for whatever tray you pick, including 10x20, 10x10, 7x14, and a custom footprint you measure yourself, which is exactly what a sprouting tray needs. It carries the rest of the crop's plan along with it, including soak time, blackout days, and days to harvest, so it also projects your harvest date and sends web push watering reminders. It runs in any phone or desktop browser and installs to your home screen, and the free plan covers 2 active trays.

Step 3, Seed evenly

Using your hands or a seed shaker, spread the seeds as evenly as possible across the grow medium. Try not to group seeds together in clumps. Even coverage equals even germination.

Seeding a sprouting tray with microgreen seeds spread evenly across the medium

Step 4, Water in

Use a spray bottle or hand pump sprayer (best) to water the seeds and medium generously. You want everything moist, not soaking, not dripping, just thoroughly damp. Too much water at this stage is one of the leading causes of mold and slow germination. For volumes and technique across every stage, see our complete guide to watering microgreens.

This is our favorite misting device for all mediums.

Mandi watering sprouting trays that have been seeded with microgreen seeds

Step 5, Cover and add weight

Remove the green tray from underneath, knock out any medium that may have fallen into it, and place it on top of the seeds as a cover.

At this point you have two options: add a 5 to 7 lb weight on top of the green tray, or leave the tray as-is and let it act as the weight on its own. The amount of weight needed varies by crop variety, we have this listed in our free Tray-Specific Seeding Guide PDF along with suggested timing, using W = Weight or ET = Empty Tray so you always know what each variety needs. Weight can be really beneficial for even germination and seed hull removal. Want to see the exact timing in action? Our weight to blackout transition guide walks through it step by step.

Mandi placing green bottom tray on top of microgreen seeds during germination

Adding weight on top of microgreen seeds during germination phase

Step 6, Germination

Place your tray on a dark shelf. Check and water twice daily, morning and evening. Keep the medium consistently moist. Most crops will germinate in 2 to 4 days. You'll know they're ready to move to the next step when you see more yellow plant coming through than dark seed coatings, and the tray or weight is starting to lift from the pressure of the seedlings pushing up.

Step 7, Blackout

Remove the weight and cover tray. Give your seedlings a mist, then take the green tray, flip it upside down to create a dome, and place it over the mesh tray. Put the whole setup back on a dark shelf for 1 to 2 days depending on the variety. The goal here is to give the stems a little stretch so they're taller and easier to harvest. Don't overdo it though, too much blackout leads to a lanky crop that topples over. Pulling them into light too early has the opposite problem, which we cover in why your microgreens are staying short.

Putting microgreens into blackout phase using a sprouting tray

Step 8, Move to light and begin bottom watering

Once your crop is the right height (a slight stretch is perfect, not flopped over), flip the green tray back underneath the mesh tray so it acts as a reservoir. Move your crop to light for the first time.

This is where the sprouting tray becomes a little different from working with 10x20 trays. There's often a noticeable gap between the bottom of the mesh tray and the base of the green tray. Because of this, you'll need to add significantly more water than you might expect when you first start bottom watering, usually around 2 to 2½ cups to start, compared to the ¼ cup you'd begin with in a standard 10x20 setup.

The way to check: add water, let the tray settle, then slightly lift the mesh tray and look for water droplets on the underside. If you see them, you're good. If you don't, add a bit more. You want the roots making contact with the water to prevent your microgreens from drying out. The bottom of the tray itself does not need to be sitting in water, just the roots.

For best results under light, see our complete microgreen lighting guide, built on years of testing different setups in our own space.

Watering notes by medium:

Soil: Bottom water with plain water. We don't suggest most liquid fertilizers here, since quality soil mixes are already nutrient rich and piling more on can stunt growth or cause tip burn. Worm castings or your own experiments are fine, since every soil is different.
Coco Coir: You can boost growth by adding hydroponic nutrients when bottom watering. We use Ocean Solution 2-0-3 mixed at 0.5 oz per gallon, then pH balance the water to 5.5 to 6.0. We no longer carry it, so that link points to where we buy it now.

Check your tray twice daily. You don't want the medium staying overly saturated, if it looks and feels very wet, skip one watering to let it dry out a bit. If plants are wilting or flopping, add more water. Watering really is the key skill with these trays, and once you get a feel for it they become very easy to work with.

Every 2 to 3 days, also check whether old water is still sitting in the green tray. If so, dump it and refill with fresh water, coco coir and soil retain moisture well, so stagnant water can build up faster than you'd expect and invite disease.

Mandi of On The Grow removing microgreens from blackout phase

Adding bottom water to a sprouting tray of microgreens under light

Step 9, Harvest

Most crops will be ready to harvest in 7 to 14 days. Look for the first true leaves appearing and do a taste test to see if the flavor is where you want it. Cut above the medium and store your microgreens unwashed in a container at 35 to 40°F. Compost your used medium afterward, and our guide on what to do with used grow medium covers a few other options. For more harvest tips, see our guide on what works best for harvesting microgreens.

Radish microgreens with purple stems growing in a large sprouting tray from On The Grow

Step-by-Step: Growing with a Reusable Silicone Grow Medium

If you'd like a soil-free, reusable option, our large sprouting tray sized reusable silicone grow medium drops right into the white mesh tray, and we also carry a small sprouting tray size. Even though we no longer sell the sprouting trays themselves, both silicone sizes stay in our lineup, so if you already own sprouting trays or buy a set elsewhere, you can keep growing on a medium that holds up cycle after cycle. Here's how the process is a little different:

Step 1, Set up the tray

Place the white mesh tray on top of the green solid tray. Lay the silicone medium flat inside the mesh tray. Give it a light mist with water before seeding, this helps the seeds land and stick instead of bouncing around.

Step 2, Seed evenly

Measure your seed and distribute it as evenly as possible across the silicone surface. Mist again lightly after seeding to make contact with the seeds. If any water is pooling on top of the medium, wick it up gently with a cloth or paper towel, you don't want standing water during germination.

Seeds that work well on reusable mediums in sprouting trays include broccoli, kale, radish, sunflower, peas, cabbage, basil, kohlrabi, and most brassicas. Varieties that don't perform well on reusable mediums include Swiss chard, beets, and cilantro, stick to soil or coco coir for those. Arugula can be grown on reusable mediums but tends to have tangling roots and can be more challenging to clean afterward. For a full breakdown, check our seed compatibility guide for reusable grow mediums.

Step 3, Cover and weight

Flip the green tray over the top and optionally add a 5 to 7 lb weight. Check your free seeding guide for the recommended weight vs. empty tray guidance per variety.

Step 4, Germination

Same as soil and coco coir, dark shelf, mist twice daily, 2 to 4 days for most crops.

Step 5, Blackout

Once germination is complete, mist the seedlings, flip the green tray upside down as a dome, and blackout for 24 hours just like with soil or coco coir.

Step 6, Move to light and bottom water

Remove the green tray on top and move your crop to light. The same watering gap applies here, start with 2 to 2½ cups and check for moisture and root contact under the mesh tray.

With reusable mediums, we highly recommend adding hydroponic nutrients when bottom watering. Unlike soil, a reusable silicone grow medium is completely inert, meaning it contains no nutrients of its own. There's nothing in the medium to feed your plants, so the only way they're getting nutrition during the grow is through the water you give them and the grow lights. Skipping nutrients with a reusable medium means your crop is essentially growing on water alone, which can result in slower growth and a lighter harvest. We use Ocean Solution 2-0-3 mixed at 0.5 oz per gallon, then pH balance the water to 5.5 to 6.0. For other options and ratios, see our best nutrients and fertilizers guide.

Step 7, Harvest and clean

Harvest as normal. After harvest, hand wash the silicone medium with warm water and a mild, food-safe dish soap like Dr. Bronner's or Seventh Generation. Use your hands rather than a brush. Between crop cycles you can also boil it for 2 to 3 minutes to deep sanitize. Once cleaned and dry, it's ready for the next grow. For a deeper dive on care, see our cleaning and sanitizing guide for reusable grow mediums, and our full overview of the reusable silicone grow medium covers the specs.

Common Troubleshooting Tips

Crop falling over: Usually an under watering issue with these trays due to the gap between the mesh and green tray. Check root contact with water first. Could also be over watering or a pathogen, check the roots. Sliminess or localized die-off points to disease, not watering.

Over watered medium: If the medium is visibly saturated and waterlogged, skip one watering entirely. Even after a full day off, the crop should still have enough moisture. For reusable mediums, if water is pooling onto the medium above, simply pour out a splash of water until it's not happening any more.

Stagnant water smell: Dump the old water from the green tray every 2 to 3 days and replace with fresh. Don't let water sit.

Mold during germination: Usually caused by too much water at seeding, poor airflow, or over watering during germination. Reduce spray amount, ensure you're on a dark shelf with reasonable airflow, and don't seal the tray so tight that no air gets in. For more, see our mold prevention guide.

Seed hulls not coming off: Make sure you're using weight during germination for varieties that need it. The weight pressing down on the tray makes contact with the seeds and helps dislodge those hulls as the plants push up.

For more common pitfalls, check our blog on the top microgreen growing mistakes and how to avoid them.

Frequently Asked Questions

Are sprouting trays good for microgreens?

Yes. Sprouting trays weren't originally designed for microgreens, but they work very well once you understand the watering quirks. They're more affordable than 10x20 trays and fit into smaller spaces, which makes them a great option for home growers.

How much water do I add when bottom watering a sprouting tray?

Start with 2 to 2½ cups due to the gap between the mesh tray and the green reservoir tray. Lift the mesh tray slightly to check for water droplets underneath, if you see them, you're good. If not, add a bit more until the roots are making contact with the water.

How much seed do I use in a sprouting tray?

A large sprouting tray is roughly half the footprint of a 10x20, so start at about half your usual 10x20 rate. That means roughly 10 to 20 grams for small seeds like broccoli, kale, and radish, about 65 grams for sunflower, and about 120 grams for peas. Our free Tray-Specific Seeding Guide PDF has variety-by-variety numbers, and Microgreen Tracker will scale your seeding rate to a custom tray footprint automatically if you'd rather not do the math each time.

Can I use the same sprouting tray for multiple grows?

Yes. The trays themselves are reusable. Clean them between grows to prevent disease carryover, and pair them with our reusable silicone grow medium if you want a fully reusable setup.

What seeds grow best on a reusable silicone grow medium in a sprouting tray?

Broccoli, kale, radish, sunflower, peas, cabbage, basil, kohlrabi, and most brassicas do well. Swiss chard, beets, and cilantro should stay on soil or coco coir. Arugula technically works but the tangling roots make cleanup more difficult.

Does On The Grow still sell sprouting trays?

No. We no longer sell the sprouting tray sets themselves, though they're easy to find from other retailers and the ones we recommend are in our Amazon sprouting tray list. We do still sell the large sprouting tray reusable silicone grow medium and the small sprouting tray reusable silicone grow medium for everyone growing in these trays.

Do I need to add fertilizer when growing in a sprouting tray?

It depends on your medium. Quality soil mixes already carry nutrients, so we don't suggest adding liquid fertilizer there. Coco coir and reusable silicone are inert, so we highly recommend adding Ocean Solution 2-0-3 at 0.5 oz per gallon, pH balanced to 5.5 to 6.0.

Final Thoughts

Sprouting trays have a learning curve, mainly around watering, but once you've got that dialed in, they're genuinely one of our favorite trays to use. They're affordable, compact, and they produce great results across all three grow medium types. And even though we no longer sell the trays themselves, the large and small sprouting tray reusable silicone grow mediums are staying in our lineup so you can keep growing in the trays you already own.

If you want to go deeper on growing microgreens from start to finish, check out our Beginner's Guide to Growing Microgreens PDF, it's a great starting point if you're just getting into growing and want everything laid out in one place. We also have our Tray-Specific Seeding Guide which covers sprouting tray seeding rates for multiple crop varieties, our book Becoming a Microgreen Master, and our full Microgreen Masterclass course for growers who want to go all in. When you're ready to keep your trays organized, you can create a Microgreen Tracker account.

Beginner's Guide to Growing Microgreens PDF from On The Grow

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This post contains affiliate links. We may earn a small commission on qualifying purchases at no extra cost to you. We only link to products we use and recommend.

The results and opinions shared in this post are based on our own first-hand testing in our specific, controlled grow space. Any mention of a brand or product reflects our own experience, not a sponsored or definitive review. Your climate, water, seed, and setup are different from ours, so your results can vary. We always encourage you to run your own experiments and see what works best for you.

Happy growing!

How to Grow Microgreens in a Sprouting Tray
Published: October 29, 2021
Updated: August 7, 2026
All content is property of On The Grow®, LLC

I want to reuse my growing medium so what do I use?

Millie April 28, 2025
Love your videos! Can you send me the free downloadable microgreen grow guide? And yes, I be-leaf in magic too!

Lisa Willie February 15, 2023
I’m so enjoying watching you two! So informative and you guys really know your stuff! Can you send me the free downloadable microgreen grow guide? I watch every video you make. Thank you On the Grow! I Be-leaf in magic too!

Lisa Willie February 15, 2023