A wide variety of minerals, vitamins, and antioxidants – microgreens have it all. Adding microgreens to your daily meals is the way to go if you are looking for a boost of nutrients in your diet. And they will also make your meals look and taste amazing! Since we can use seeds from any salad vegetable for growing microgreens, there is a wide variety of flavors to choose from. However, commercially grown microgreens are often expensive, especially considering how cheaper it is to grow them at home. Another benefit of growing your own batch of microgreens is that you can create any combination you like and always have them fresh. Every crop starts progressively losing its nutritive properties after the harvest, so having fresh produce ready at home is a big advantage.
Microgreens are generally easy to grow after you get to know them, but the path toward that point can get quite tumultuous. Mastering the art of growing microgreens or any plant whatsoever is a lot easier when you know what not to do. With that principle in mind, today we’ll talk about the things that are best avoided in growing microgreens. Keep an eye not make any of these seven common mistakes, and you’ll have healthy, bountiful harvests of your favorite microgreens in no time.
1. Using unviable seeds
If you have ever sown your microgreens only to find empty patches of soil, you likely used a batch of unviable seeds. This problem often occurs with seeds collected from unhealthy plants, seeds stored in unfavorable conditions, as well as with undeveloped, old, and damaged seeds. It happens far more often with foraged than commercial seeds since the latter go through quality control.
If you prefer using your own seeds, it is always best to inspect them before sowing. During the inspection, remove the seeds that look undeveloped, old, or visibly damaged, as well as the ones with strange discolorations and/or irregular shapes. The viability of such seeds is likely very low. Besides wasting time and resources, non-viable seeds also reduce growth density, which can negatively affect the plants that have managed to germinate. We’ll talk about why this is unfavorable in greater detail in the next section.
2. Too low or too high seeding density
Optimal seeding density is essential in growing microgreens. Being too humble or too generous can have a very negative effect and leave you with a poor yield. The sprouts support each other as they grow, so if the seeding density is too low, they tend to bend and fall down. On the other hand, if the seeding density is too high, the sprouts can grow unevenly as they compete with each other for space and light. This leads to dominant growth of some sprouts and stunted growth of others. High seeding density also makes it harder for air to get between the sprouts, increasing humidity levels. Poor aeration and the abundance of moisture create perfect conditions for molds to thrive.
The optimal seeding density can significantly vary between different types of microgreens. However, you don’t need to go through endless literature and do complex calculations to find out how many seeds you need according to the size of the available growing area. There are specialized calculators that can do the math for you. A number of microgreen seed density calculators are available in the app store, just find the one that works the best for you.
3. Overwatering or underwatering
Improper watering is probably the most common problem in growing microgreens. Since they are far more sensitive than mature plants, microgreens can easily succumb to pathogens or oxygen deficiency brought by excess moisture in the environment. The other extreme is also bad; when there is too little moisture, the seeds aren’t able to germinate and the sprouts wither and dry. Microgreens need to have a constant source of moisture, otherwise they fail to develop properly.
The substrate should never reach the point of being completely dry, but it also shouldn’t be drenched. The goldilocks zone is when the substrate is evenly moist but not heavy and draining. For this reason, it is best to avoid top watering microgreens. Instead, add water to the tray saucer and mist the growth if the air humidity is too low. Bottom watering and misting provide a more even distribution and greater control over water use. Another beneficial strategy for keeping moisture levels in check is to add smaller amounts of water more frequently. This does cost more time and care, but can significantly reduce the risk of overwatering and moisture buildup.
The situation is a bit different with microgreens grown hydroponically since there is no substrate in the traditional sense. However, the problems in hydroponics are similar to the overwatering problems with microgreens grown in solid substrates. Since the water is constantly evaporating, the vapor can accumulate between the plants and invite molds and pathogens that cause root rot. This often happens when the temperatures are high, as the evaporation rate intensifies. For that reason, it is very important to keep your hydroponic garden well-aerated, and if you cannot achieve it naturally, consider adding a fan.
4. Choosing an unsuitable substrate
The choice of substrate can really make or break your microgreen garden. Luckily, there are multiple options to choose from, so you can pick the one that optimally suits your needs. Microgreens can be grown in soil and other solid substrates and in hydroponic and aeroponic systems. Depending on the growing method you use and the size of the growing operation, some substrates are simply better and economically more viable than others. Let’s run through the most common substrates for microgreens, and their advantages and disadvantages.
Soil
Soil is the cheapest substrate, and there are many growers who prefer it, not only because of its affordability but also because it gives good results. However, microgreens cannot thrive in any type of soil. If you tried to grow microgreens in regular potting soil, you probably encountered some problems. Standard potting mixes are often too heavy and coarse for growing microgreens. They can also be too “dirty”, as their microbial diversity can also include some potentially nasty pathogens. Young plants are more susceptible to infection, and the moist environment they require to thrive surely doesn’t help, as it is the perfect breeding ground for various harmful molds and bacteria.
Soil for microgreens needs to have a light structure and be able to retain moisture. In such a substrate, the roots can develop effortlessly and have a steady source of water. The light, aerated structure of the soil also ensures there are no anoxic pockets that can harm the roots or invite pathogens.
Some growers recycle old soil, mix it up with some fertilizer and use it as a substrate for growing microgreens. However, this practice is generally not advised, since the recycled soil can be contaminated with pathogens or compounds that are harmful to seedlings. The substrate should be as sterile as possible to avoid contaminations but also ensure nutrient availability to young sprouts.
Alternatives to soil
While they do grow better in substrates with better nutrient availability, microgreens aren’t that picky in terms of soil richness. The physical properties of the substrate play a far more important role. Because of this, there are multiple ways to successfully grow microgreens, and some of them don’t include soil at all. Since water availability is one of the primary prerequisites for growing microgreens, the primary desired quality of the substrate is moisture retention. The most common soilless substrate for growing microgreens is a mix of coconut coir, sterilized compost, and perlite. This combination has very favorable moisture-retaining qualities and provides the right structure for the plant roots.
Peat moss?
Some growers like to use peat moss as a microgreen substrate, but we advise against that practice. Peat moss is a resource that comes from exploiting peat bogs, which are important, biodiverse ecosystems that support numerous species of plants, animals, and microorganisms. Peat bogs also play a significant role in carbon sequestration, which means that they are very effective in storing and removing CO2 from the atmosphere. As such, they provide a free, powerful, and completely natural method of reducing CO2 levels.
Grow mats
Grow mats are made from a variety of natural materials – coco coir, hemp, burlap, and wood fiber are the most common. Mats are most commonly used as substrates for hydroponic production due to their favorable physical qualities. Since they often are not very abundant in nutrients, grow mats require an application of fertilizer. In hydroponics, this is not a problem as nutrients are added to the irrigation water.
Grow mats can be very clean and efficient, but some require skill and fine-tuning to work successfully. Their quality is also an important factor because low-quality ones can really ruin your batch. If the material is too loosely woven, the seeds can fall through the strands, and if the strands aren’t strong enough the mat can fall apart. All in all, mats can be very fun and high-yielding but not very kind to beginners.
Pay attention to the depth of the substrate
Choosing trays that are deeper than 1.5 inches and filling them to the top with the substrate is another common mistake. This practice can waste a large amount of substrate, which can be very expensive if you are using quality mixes. It also increases water use, as more water is necessary to satiate the volume of the substrate and maintain favorable humidity levels. A one-inch layer is often completely enough to support the microgreens, provide nutrients, and enable the roots to create a thick mat.
Overfilling the trays with soil can also make the harvest very messy and get the greens dirty. While this is not a great deal in home settings, it can be problematic in commercial microgreen production.
5. Using pots and trays made of harmful plastic
When plastic wears out and decomposes, it can release some pretty nasty compounds you don’t want anywhere near your food. Because of this, it is very important to pay attention to the type of plastic in the microgreen trays. The best solution is to ditch plastic entirely and find adequate safe and biodegradable alternatives, like egg cartons, coconut trays, aluminum pie pans, and various upcycled and recycled materials. However, if you need to use plastic trays make sure they are made of food-safe plastics. Food-safe plastics include high-density polyethylene (HDPE, 2), polypropylene (PP, 5), and acrylonitrile butadiene styrene (ABS).
6. Improper lighting
A bad lighting setup and regime can cause low germination rates, as well as slow or stunt the growth of your microgreens. Just like most other plants, microgreens require a different amount of available light in different growth phases. Seeds generally require a period of darkness to germinate successfully, so exposing them to light after sowing can have a suppressive effect on them.
The dark phase
Putting a blackout dome over the microgreen tray ensures that the seeds have favorable conditions for germination. It also retains moisture, which helps to prevent drying and reduces the need for watering often. After the sprouts emerge after a couple of days, their first leaves will have a yellowish color. This is not a reason for concern because it is completely normal for plants that didn’t receive light. Once you move the sprouts to a lighted place, their chlorophyll will activate, and the leaves will begin photosynthesizing.
The light phase
After the dark phase, the young sprouts need light to continue developing and growing. Two to three days after the sprouting becomes visible, the dome should be taken off. If done too late, the seedlings may lose energy and fail to develop properly. The tray should be placed in a sunny spot or under a grow light. The next thing to consider is the intensity of light and length of exposure. In case of limited light availability, the sprouts will grow very slowly and have a pale green, yellowish color. On the other hand, intense light and prolonged exposure can exhaust and burn them. Microgreens prefer 10-14 hours of light during the day, with the exact number depending on the specific crop or its variety. Cold weather crops work well with 10-12 hours of light, while warm weather crops need 1-2 hours more.
To provide the optimal light intensity and exposure to your microgreens, it is best to grow them under artificial lighting. Another advantage of using grow lights is that you have fresh microgreens all year long, no matter where you live.
7. Unintentionally attracting pathogenic fungi and bacteria
As mentioned, microgreens are susceptible to molds and other pathogenic organisms that thrive in humid, warm conditions. Pathogens can come from low-quality substrates, contaminated tools, or other infected plants. They can also be accidentally brought into the growing room on hands and clothes, or with the microgreen seeds. Prevention is the key to avoiding diseases, so maintaining good hygiene in all aspects is very important. The seeds, substrate, tools, and the growing environment all need to be as clean as possible. Removing every single spore and bacterium is practically impossible, but reducing their numbers to a minimum can certainly help. Another important factor is moisture. In the part about overwatering, we discussed how the excess moisture in the substrate can invite various pathogens. As a result, we can easily consider proper watering as another disease-prevention strategy.
Some of the most common microgreen pathogens include grey mold (Botrytis cinerea), white mold (Sclerotinia sclerotiorum), and root rot (Pythium sp., Fusarium sp., Rhizoctonia sp.). The gray mold, as its name indicates, is easy to recognize by its dark gray growth, but white mold can be a bit tricky. Less experienced growers can often mistake mold mycelium with root hairs and vice versa. There are a couple of key differences that can help easily distinguish between the two. Firstly, root hairs are shaggy and always attached to the root, while mold mycelium creates thin threads that resemble webbing from spiders or mites, and grows over the substrate and the plants. Your sense of smell can also help – molds have a peculiar musty odor, while healthy root hairs don’t.
In a nutshell
When growing microgreens you want to pay attention to:
- the health and maturity of the seeds
- seeding density
- structure and physical qualities of the substrate
- maintaining favorable humidity levels
- lighting – intensity and length of light exposure in different growth phases
- hygiene – preventing pathogen infections
- use microgreen trays made of food-safe materials
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Ana Mileusnic
Ana is a scientific writer and researcher passionate about sustainable agriculture and environmental protection. As a speleologist in training and a member of the Bird Protection and Study Society of Serbia, she is involved in field research and various projects related to ornithology and biodiversity conservation in her home country.
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