It's harvest day, but your microgreens look…sparse. Or maybe they took far longer to grow than expected. Low yields and slow growth are two sides of the same coin - your microgreens aren't producing the volume or speed you hoped for. Don't despair: with some sleuthing, you can often pinpoint why your microgreens are underperforming. This troubleshooting guide will help you examine possible reasons for a thin harvest or sluggish growth and how to turn things around. Let's get those microgreens growing like they mean it! 💪🌱
1. Seed Quality and Viability
The journey to a bumper crop begins with the seed. Old or poor-quality seeds can result in low germination rates, which directly leads to low yields (fewer plants growing means less to harvest). Seeds lose viability over time, especially if not stored properly. Also, cheap seeds might have low germination percentages to start with.
Solution: Use fresh, high-quality seeds with known high germination rates. Check the seed packet or supplier info for germination rate - many reputable suppliers (like Deliseeds 😉) will list something like "Germination: 95%". If you're unsure about your seeds, do a quick germination test: place 10 seeds in a damp paper towel for a few days and see how many sprout (this gives a rough percent). If it's much lower than expected, get new seed stock. Also, store your seeds in a cool, dry place to keep them viable longer.
Sometimes, seed quality can vary by batch. If you suspect a bad batch, try a different batch or brand for comparison. One community tip: "Always buy fresh seeds for microgreens for the best results" - it really makes a difference.
2. Seeding Density: Not Too Little, Not Too Much
Striking the right balance in how densely you sow seeds is key to yield. Too few seeds = a tray that's half empty, no matter how well those few grow. Too many seeds might sound like it'd yield more, but it can backfire - overcrowding can cause stunted growth, mold, or damping off, reducing overall harvestable yield.
If your yield issue is simply that the tray looks patchy, you might not be using enough seeds per tray. Perhaps you were trying to economize seeds, but for a full yield you generally need to sow thickly (each variety has an optimal range, e.g., ~10-12 grams for a 10x20" tray of radish, etc.). Check recommended seeding rates - under-seeding is a common reason for a disappointingly small harvest.
On the flip side, if you dumped the whole packet in there, the competition among too many seedlings could result in many thin, weak microgreens that don't add up to much weight. Overcrowding can also cause more seeds to fail (rot instead of grow) due to lack of space and airflow.
Solution: Calibrate your seeding. Follow guides or charts for how much seed to use for your tray size and seed type. For example, you might use ~30g of sunflower seed for a standard tray, but only ~6g of broccoli (because seeds differ in size and optimal spacing). If you had low yields due to bare spots, increase your sowing rate gradually. If you had masses of tiny, yellowish, or moldy seedlings, reduce it a bit to give them breathing room. A denser sowing typically yields more up to a point - find that sweet spot per variety.
3. Environmental Factors: Light, Temperature, Humidity
Microgreens grow best in a Goldilocks zone of environment. If they're growing too slowly:
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Light: Insufficient light after germination can slow growth significantly. Microgreens in low light don't photosynthesize enough, so they grow slower and often end up smaller (and leggier). They also might yield less because they don't develop as much foliage. Even if they eventually reach size, it took longer.
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Fix: Ensure strong light for at least 12-16 hours a day once you uncover them. If you're using a window and noticing slow growth, consider supplementing with a grow light. Light = energy = growth. Microgreens under proper light often surprise you with how fast they bulk up.
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Temperature: Microgreens are like people - most prefer room temperature. If your grow area is too cold, seeds germinate slowly and growth drags. For instance, at 15 °C, you might see germination and growth take almost twice as long as at 22 °C for some varieties. On the other hand, very high temperatures (above 27 °C) can stress seedlings, sometimes causing issues like damping off or just weak growth.
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Fix: Aim for roughly 18-24 °C for optimal growth. If it's winter and your place is chilly, consider a heat mat during germination or moving trays to a warmer spot. If it's very hot, ensure good airflow and maybe a slightly cooler location if possible.
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Humidity & Airflow: High humidity can be a double-edged sword. It helps during germination, but if it stays too high (with poor airflow), fungi can proliferate, which can kill or weaken many seedlings (lowering yield). Conversely, extremely low humidity can dry out seedlings quickly, stressing them (but usually, watering counters that).
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Fix: After germination, remove humidity domes and give your microgreens some air. A small fan can strengthen them and prevent disease. If you see mold killing patches (reducing yield), address that by increasing airflow and not overwatering. If growth is slow and stems rot (damping off) in overly humid conditions, that's a sign to dry things out a bit.
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Think of it this way: microgreens grow fastest when they have plenty of light, are comfortably warm, and can "breathe" without getting attacked by mold.
4. Watering: Not Too Dry, Not Too Wet
Water issues can cause both slow growth and poor yields:
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If microgreens experience drought stress (even short bouts of dryness), they may grow slower or stay stunted. If they dry out severely, many will die, obviously reducing yield.
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If they're overwatered, roots can suffocate or rot (damping off), leading to yellow, stunted growth and losses in the crop.
Solution: Keep the growing medium consistently moist but not waterlogged. In practical terms, water once you notice the surface starting to dry or the tray feels lighter, but before plants wilt. Use the bottom-watering method to provide moisture evenly without oversaturating the topsoil. Dump any standing water after a few minutes so roots aren't sitting in a bath (unless you're doing hydroponic intentionally). Remember, microgreens have shallow roots - they don't need deep watering, just consistent watering.
Also, water quality can play a role: extremely hard water or water with extreme pH could potentially slow growth (nutrient availability issues). It's minor, but if you suspect that, try using filtered water or adjusting pH. Generally, though, as long as your water is potable, it shouldn't drastically affect yield.
5. Growing Medium and Nutrients
Microgreens usually don't require additional fertilizer because they live off the seed's nutrients. But the medium can affect growth speed:
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A poor medium that compacts or doesn't hold water can stunt roots.
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If you're using a soilless medium (coco coir, mats, etc.) with zero nutrients and growing microgreens past the typical harvest time, they might indeed slow down due to lack of nutrition after the seed's reserves are used.
Solution: Use a light, well-draining medium that retains moisture. Many use peat or coir-based seed-starting mixes. Ensure it's clean (to avoid pathogens). If you consistently see slow growth with a particular medium, you could experiment with a different one (some growers swear by soil for a more robust growth vs. just fiber mats).
If you're pushing microgreens beyond ~10-14 days (maybe aiming for larger pea shoots or sunflower shoots), a very dilute nutrient solution could help after the first week. For example, hydroponic growers sometimes add a quarter-strength hydroponic fertilizer for longer-grow microgreens. This can boost biomass a bit. But be cautious: too much fertilizer can cause burns or unwanted flavor changes. It's usually unnecessary for standard microgreens harvested at the cotyledon stage.
6. Variety Matters
Not all microgreens yield the same or grow at the same pace. If you're comparing, say, radish microgreens to cilantro microgreens, you'll notice radish practically explode in a week with a heavy yield, whereas cilantro is slow (can take 2+ weeks just to germinate fully) and yields less because it's an herb with fine stems.
So, if your yields are low, consider if the variety has inherently lower yield. For instance:
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Pea shoots and sunflower usually give high yields because they're bigger and you sow heavily.
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Radish, broccoli, kale - quick and decent yield.
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Basil, bull's blood beet, cilantro - slower germination, often smaller yields and longer grow time.
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Amaranth - beautiful but yields lighter due to very small size.
If you grew a notoriously slow or low-yield microgreen, the "fix" might simply be adjusting expectations or switching to a more prolific variety if maximum yield is your goal. Alternatively, sow a thicker layer of those slow herbs to get more plants.
Solution: Match your expectations to the crop. For a business or lots of volume, focus on fast, high-yield varieties (like the brassicas, pea, sunflower). If you love the slow herbs (they have great flavor), just plant more trays in succession so you still get enough over time. Sometimes people think they did something wrong when really, for example, fenugreek microgreens just don't yield as much mass as sunflower in the same time.
7. Harvest Timing
Harvest timing can affect perceived yield and regrowth. If you cut microgreens too early, obviously yield (weight/volume) will be less. If you wait a bit longer (to a point), they'll have more mass. However, don't wait so long that they start declining (yellowing or using up nutrients).
Most microgreens are optimal at a certain height or days after sowing:
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Radish: ~10 days.
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Broccoli/Kale: ~8-10 days.
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Pea Shoots: ~12-14 days.
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Sunflower: ~8-10 days.
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Basil: ~16-20 days (they're slow).
If you were over-eager and cut, say, on day 5 a crop that normally needs 8 days, you shortchanged your yield.
Also, note that most microgreens (apart from pea, maybe) do not regrow after cutting. So you get one harvest per sowing. Trying to let them regrow usually won't work (they don't have enough stored energy to regrow significant second shoots). Better to start a new batch. So plan successive plantings rather than hoping to "cut and come again" (except pea shoots can sometimes give a modest second flush if you leave some leaves, but even that is limited).
Solution: Harvest at the right time - when cotyledons are open and maybe first true leaves just emerging (depending on taste preference). Use multiple trays in a staggered schedule if you want continuous yield. This way, while one tray is being harvested, another is just starting, etc.
8. Pests or Disease Losses
It's worth mentioning: if something like fungus gnats or aphids got into your microgreens, they could damage some plants and reduce yield. Or if a section damped off (fungal disease), those plants are gone. These are less common in the short microgreen cycle, but possible.
Solution: Keep things clean to avoid pests/disease. If noticed, remove affected parts and treat if appropriate (like sticky traps for gnats, or in worst case scrap a tray that's diseased).
Bringing It All Together
To troubleshoot low yield or slow growth, think of the microgreen growth equation:Yield = (Number of healthy plants) x (size of each plant).
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Number of healthy plants is affected by seed germination (seed quality, density, germination conditions) and survival (no damping off, etc.).
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Size of each plant is affected by light, water, nutrients, and time (and variety genetics).
By optimizing each factor above, you maximize both the number and the size (to the ideal point for microgreens), thus yield.
Don't be discouraged - microgreens are quick to grow, which means you can try again and see improvement within weeks or even days. Adjust one factor at a time and observe. Perhaps sow a bit thicker and give more light and see your next radish crop double in volume. Or raise that room temp by a couple degrees and watch your broccoli finish two days sooner.
Finally, choose the right varieties for your needs. If you need volume, grow the hearty ones like sunflower, radish, pea. If you need flavor highlights and don't mind lower yield, grow the specialty herbs.
At Deliseeds, we ensure our microgreen seeds are high-germination and vigor, giving you a strong start. Combine that with the correct techniques from this guide, and your next microgreen harvest should be much more satisfying - both in quantity and speed. Happy growing, and may your microgreens grow thick and fast! 🚀🌱