Why Are My Microgreens Yellow? Causes & Cures

Nothing is more disappointing than expecting a tray of lush green microgreens… and finding pale yellow instead. 😟 Yellow microgreens (a condition akin to chlorosis, or lack of chlorophyll) are a common issue with a few different causes. The good news is that yellowing is often fixable - and sometimes, it's even normal. In this guide, we'll explore why microgreens turn yellow and how to turn them green again. By understanding the causes - from lighting to watering and more - you'll be able to diagnose your yellow microgreen woes and cure them for future harvests.

First, Is It Actually a Problem?

Let's clarify one thing: If your microgreens are yellow right when you uncover them from darkness, that's perfectly normal. All seedlings emerge yellow when they've been grown in the dark. They haven't performed photosynthesis yet, so they have no green pigment. As soon as they get light, they should start to green up. So, if you just ended the blackout period and your sprouts are yellow, give them some hours of light and check again later before worrying.

Yellowing becomes a concern if:

The microgreens stay yellow or pale for a day or more after being exposed to light.
They were green before, but later turned yellow or developed yellow patches.
They are yellow and appear unhealthy (wilting, stunted).

Now, let's go through the common causes of yellow microgreens that do indicate an issue.

Causes of Yellow Microgreens

1. Not Enough Light (Primary Cause): Light drives the production of chlorophyll (the green in plants). If microgreens don't receive sufficient light intensity or duration, they can remain yellowish or pale green. This often happens if:

You forget to take the cover off soon enough, leaving them too long in the dark (they stretch and yellow).
They're grown in a low-light setting (dim room, north-facing window, short winter daylight).
The grow light is too weak or too far from the plants, so they aren't getting what they need.

Essentially, without adequate light, they can't "charge up" to a rich green color. You may see leggy, thin seedlings hand in hand with this cause, as they stretch for light.

2. Natural Transition (Temporary): As mentioned, microgreens fresh out of blackout will be yellow. Also, the seed leaves (cotyledons) of some species might yellow and drop off naturally once the true leaves start growing. For instance, if you grow microgreens a bit longer until true leaves form, you might notice the initial leaves yellowing. This is normal - the plant is reallocating nutrients, and those early leaves aren't needed anymore.

3. Nutrient Deficiency (Rare in Microgreens): In longer-grown microgreens or those grown in pure water, a lack of nutrients (especially nitrogen, which is key for green color) can cause yellowing. Generally, microgreens contain all the nutrients they need in the seed for up to 10-14 days. However, if you go beyond that (say trying to grow microgreen into baby greens) or if your medium is completely inert and you push the growth duration, they might eventually use up what's in the seed and start to pale. For example, if someone tries to grow a microgreen for 3-4 weeks with no fertilizer, nutrients get depleted and yellowing can occur.

4. Overwatering / Poor Drainage: Constantly wet, waterlogged conditions can lead to root problems. If roots can't get oxygen, they struggle to take up nutrients and the plants can yellow and wilt. Overwatering also promotes fungal diseases like damping off, which can make plants look weak, droopy, and discolored. If your microgreens are yellow and the soil is sodden or smells bad, this could be a factor. Often this shows up as patches of yellow or mushy seedlings, rather than the whole tray uniformly pale.

5. Underwatering (Dryness): On the flip side, if the medium dries out too much, the seedlings can start to wilt. Early wilting might make them look a bit faded or less vibrant green. Prolonged dryness will outright kill patches (turning them brown eventually). Tiny microgreen roots don't have much reserve, so if they go dry even for a short time, some leaves may yellow or die off. Wilting from dryness is usually accompanied by the soil feeling dry to the touch and plants looking limp.

6. pH Imbalance: This is an less common cause, but extremely high or low pH in your water or medium can lock up nutrient availability and cause yellowing. For instance, if using tap water that's very alkaline (pH 8+), a few growers have reported consistently paler microgreens, which improved when they adjusted water pH down into the 5.5-6.5 range. This is usually a concern for hydroponic microgreens where water is the main source of nutrients. In soil, pH is buffered, but it's worth mentioning if everything else seems right and you still get yellowing.

7. Disease or Pests: Some bacterial or fungal infections can cause yellow spots or general yellowing. Also, pests like aphids sucking on plant juices can lead to yellow, mottled leaves (though aphids on microgreens are rare indoors). If yellowing is accompanied by slimy stems (damping off fungus) or speckled patterns, consider disease as a cause. However, in microgreens the growth cycle is so short that diseases are less common than simply environmental issues.

Now that we know the possible causes, let's focus on solutions.

How to Green Up Your Microgreens

1. Light Therapy: If low light is the issue, the fix is straightforward: give them more light. Move trays to the brightest location you have. If using sunlight, a south-facing window or sunroom is best. For artificial lights, use a proper full-spectrum grow light if possible, and keep it close to the plants (without burning them). Many microgreens need about 12-16 hours of light each day for best color. If you've been giving much less, increase it. Within a day or two of strong light, you should see significant greening if light was the limiting factor. Keep in mind, microgreens that have been very yellow might not achieve a deep green if they were at the end of their cycle, but they will improve. Moving forward, always let your microgreens see light as soon as they're ready - don't overshoot the blackout period. As one source puts it: lack of light is the top cause of yellowing, and seedlings need light to turn green.

2. Proper Watering Practices: Check your watering schedule. Is the medium too wet or too dry?

If things were swampy, cut back on watering. Ensure you have good drainage (holes in trays) and always drain off excess water. You might switch to bottom watering so the surface stays drier. Also, increase airflow (use a fan) so that surfaces dry between waterings. As the surface dries, roots still stay moist deeper down, but mold and rot are less likely. If damping off or rot occurred (you see collapsed, brownish base of stems), promptly remove those sections and improve ventilation. Unfortunately, those particular seedlings won't recover, but you can save the rest.
If you suspect underwatering, you'll often find the yellowing at the edges or highest parts of the tray (that dry out first). In that case, step up your watering frequency a bit. Microgreens may need water daily or every other day depending on your climate. The key is consistent moisture. The soil or medium should feel like a wrung sponge - not dripping, but never bone dry. If you accidentally let it dry out and see wilting/yellowing, water immediately. Often slightly wilted microgreens will perk up within an hour of watering if caught in time. They might have some lasting yellow on the most affected leaves, but new growth will be green.

3. Quick Nutrient Boost (If Needed): Most of the time, microgreens don't require added fertilizer. However, if you're growing a slower microgreen (like basil, beet, cilantro) or using a soilless medium with zero nutrients (like plain coconut coir or paper mats) and you see the second set of leaves (true leaves) coming in pale, a mild feed can help. Use an organic half-strength liquid fertilizer (for example, hydroponic lettuce fertilizer at half the normal dose, or fish emulsion diluted well) and water with that once. This can supply a bit of nitrogen and iron to green them up. Only do this if you are extending growth beyond ~10 days or see clear signs of nutrient lack. For a typical quick microgreen like radish or broccoli harvested at cotyledon stage, nutrients in seed and any decent potting mix suffice. Over-fertilizing can cause burn or excessive growth, so less is more. Also, ensure you're harvesting on time - microgreens harvested at their prime (usually when cotyledons are fully open and before true leaves or just as they emerge) are tender and green. If you wait too long without nutrients, they may yellow.

4. Check Your Growing Duration: Are you trying to grow microgreens into full plants? Remember, microgreens are meant to be harvested young. If you let them go far beyond their ideal harvest window, they might start needing things (like nutrients, potting-up, etc.) that a microgreen setup isn't providing. For example, pea shoots are great at 10-14 days; if you push them to 21 days, the lower leaves often yellow as the plant wants a bigger root space and nutrients. So harvest on schedule. If you want bigger greens, consider transitioning to growing baby greens or full veggies, which requires different care.

5. Evaluate Water Quality (pH): If you have ruled out light and basic water issues and still see poor color, it might be worth looking at your water. As mentioned, extremely alkaline water (very high pH) can cause some nutrient lockout. Microgreens generally prefer a slightly acidic to neutral pH for optimal growth. You could test your water pH with a cheap pH strip or meter. If it's, say, 8.5, you could adjust it down into the 6s using a drop of vinegar or citric acid in your watering water (there are also pH down solutions from hydroponic suppliers). This is a more advanced tweak - for most tap water, it's not necessary. But in some locales it could make a difference, notably for hydroponic grows. Similarly, if using very hard water, mineral buildup could affect things - using filtered or rain water occasionally might be beneficial.

6. Ensure Adequate Air & Spacing: While these relate more to mold and rot, they can indirectly affect color. Good airflow as discussed prevents disease that can yellow leaves. And not seeding too insanely thick means each seedling gets its share of light and air. If yellowing is happening in the very dense center of a tray, it might be a hint that those were too crowded and some in the middle died off (turning yellow/brown) due to lack of light and air. In that case, thin out slightly next time.

When to Start Over

If your entire tray of microgreens is yellow and not improving with light within a day, it might be that they were too far gone or something fundamental was off (like very poor seeds or major nutrient deficiency from the start). In such cases, it's okay to cut losses, compost that batch, and start anew with the lessons learned. Usually though, a day under bright light performs miracles on a yellow tray. Many growers have been surprised how a sickly-yellow tray turns bright green with proper lighting and a bit of care.

Prevention for the Next Batch

Now that you've tackled the immediate issue, consider these preventive measures for future plantings:

Use a Timer for Light: If growing under lamps, use a simple outlet timer to ensure they get long consistent light daily. This avoids forgetfulness leading to insufficient light.
Check Seed Quality: Though uncommon, if seeds are very old or not stored properly, seedlings might be weaker and more prone to issues. Ensure you use fresh, high-quality seeds (like those from Deliseeds, which are tested for strong germination).
Monitor Daily: Microgreens grow fast - checking on them at least once a day (even better, morning and evening) means you catch things like drying out or the need to uncover right when it's time. The faster you respond, the less chance for yellow problems to set in.
Environment Control: Try to grow in a spot with stable conditions. Avoid windowsills that get very cold at night (cold can sometimes cause slight yellowing too, as nutrient uptake slows). Also avoid spots with no ventilation at all. Aim for that sweet spot of bright, mild, and fresh air.

Enjoy Those Greens!

Yellow microgreens can be a bummer, but in many cases they're just asking for light or a minor care tweak. Once you correct the issue, they'll reward you with that rich green hue that not only looks appetizing but also indicates a high nutritional content (those greens are full of chlorophyll and vitamins). And if you did have to toss a truly failed batch, don't be discouraged - it's all part of the learning process, and microgreens by nature invite experimentation. Your next crop will be better.

At Deliseeds, we're here to support your growing journey. Our premium seeds give your microgreens the best start - vigorous seedlings that readily turn green under the right conditions. With the tips in this guide, we hope you'll troubleshoot any yellowing issues and be back to growing a countertop garden that's as green as a summer meadow. Happy growing, and may all your future microgreens be emerald green and bursting with life! 🌱