Frequency Asked Questions

Below are some of the frequently asked questions I receive from emails, comments, and social media. If you can't find the answer here or in one of the articles linked below, please send me your question in the form found at the bottom of the page.

Can you use the soil again?

The short answer is no, you shouldn't. More often than not, the next tray of microgreens planted in the used soil will develop damping-off disease.

damping-off disease of microgreens

The best practice is to use fresh soil for new seeds. 

Are microgreens the same as sprouts?

No, they're not. Although the same seeds can be used, the way sprouts and microgreens are grown and consumed is different. To learn more, click the button below.

I bought Home Microgreens trays, why aren't there holes in the bottom?

The watering tray (the one without the holes) nests in tight to the planting tray. Use your fingernail or a knife to separate the two trays. 

When do I bottom water?

We don't add water to the watering tray until the microgreens are placed under the light. Usually, the soil is moist enough that day, and we bottom water the first time the next morning. For those that are not placed in a blackout, like lettuce, we start bottom watering the day after the humidity dome is removed.

Is this fungus?

microgreen root hairs

The white hairs shown in the above image are  root hairs on Red Arrow Radish microgreens and are to be expected. They will either be absorbed by the plant or enter the soil (not sure which). These are good!

Below is fungus growth on sunflower microgreens. The fungus has a more fuzzy look than root hairs. This fungus was treated with food-grade hydrogen peroxide and disappeared.

Fungus on sunflower seeds

When do I harvest my microgreens?

When to harvest is subjective to the taste of the individual and the variety of microgreen. Some microgreens such as celery, cilantro, and basil shouldn't be cut until they develop true leaves.

Other microgreens, like radishes, kohlrabi, cabbage, and broccoli, should be harvested in the cotyledon stage at 3 or 4 inches in height.

Microgreens like mustards and kales can be harvested during either stage, depending on the taste characteristics of  the consumer.

What's the difference between a weighted blackout and using a blackout dome?

soil for microgreens test weighted trays

The trays of microgreens in the above photo will be going into a weighted blackout period once a towel or some other light blocking material is placed over the trays. The weight helps make seed-soil contact and forces the roots to penetrate deeper into the soil. 

shallow tray under the blackout dome

A blackout dome shields the seeds from light and keeps the humidity high inside the dome. No weight is used to improve seed-soil contact. Most microgreens that are grown well using this method are mucilaginous and adhere to the soil with the gel-like substance. The mucilage also helps the seed remain moist.

Why can't I use a clear clamshell as a tray?

The short answer is that you can use those used clear clamshells if you want. However, we have found that microgreens grow better in trays that don't let light penetrate. Not sure why. There are more reasons why we don't recommend growing microgreens in clamshells. These will be published in a future article and podcast.

Stay tuned. 

What size planting tray should I use?

There are many ways to look at this question. As far as volume, you don't want to grow more microgreens than you'll eat in a week (the average time microgreens stay fresh in the refrigerator if you have to harvest them). 

The question is, how many different varieties do you want to grow at one time? I know we like to have several growing at once, so we have a choice of micros for the food we fixing, or have several different flavors and  increased nutritional value on our salads. 

We recommend small trays between 35 and 40 square-inches the perfect size. They fit into larger watering trays, will slide onto a narrower shelf if necessary, but still provide several servings per tray. Home Microgreen planting trays are a perfect size. But if you have a big family or eat a lot of microgreens, 10 by 10 shallow trays are also an excellent size.

What's the big deal with Home Microgreens Trays?

A self-serving question? Maybe, but we genuinely do believe that our Home Microgreen Trays are a big deal. We will write an article and produce a podcast on the trays soon. 

But in the meantime, here are our beliefs.

  • The trays are inexpensive.
  • The dual tray system is utilized in many different configurations, both for weighted and dome blackouts. The lids are useful as covers or watering trays.
  • The trays have much narrower bottoms than tops, providing a large surface area to soil volume. Meaning you need less soil to fill the trays while still having a lot of room to grow seeds.
  • Water is quickly absorbed through the holes in the planting tray. The watering tray fits the planting tray tightly so water is forced up into the soil. Also, the tray bottom's configuration allows extra water to completely drain if need be. 
  • The food-grade plastic is durable, can be washed and sterilized by hand or in a dishwasher. They will last for years with regular use.
  • We have found that the planting area, about 38 square-inches, produces an ideal amount of microgreens for several servings, but not too much that will overwhelm a harvest. We suggest growing two or more trays, so you have a variety of microgreens.

These are some of the reasons we think the Home Microgreen Trays are a perfect choice.

Do I need to fertilize my microgreens?

No, you do not usually have to fertilize microgreens. However, there are a couple of exceptions (isn't there always?). You may need to add fertilizer if you're planting in pure coir or peat moss after 10-days. Neither of these products is fertile.

The second exception is for any of the long-term growing microgreens such as basil, celery, onions, or any other microgreen you're trying to grow past 21-days. We've found that an organic liquid fertilizer will improve the color of the microgreens and add a flush of growth.

Besides that, why add anything to something you're going to eat? Just because it's organic doesn't mean it's good for you.

After all, snake venom is organic.


Why use soil?

Where do 99.9% of seeds grow?

In soil, so why would we want to do anything differently? Although many say that microgreens seeds contain all of the energy they need to grow, we find this just isn't so. 

This article and those linked within explain and show why soil is best. When you see the differences in the photos, you to will see why we use soil.

Soil is messy, what can I do?

Soil can be messy if it's spilled or not contained, but that shouldn't preclude you from using it.

We place the planting tray inside of a larger plastic tray, like a washbasin or some container with low sides and larger than the planting tray. 

If the soil spills while filling the tray or planting the seeds, it doesn't go on the table or floor. The larger container will stop the mess from happening.

Once you've wet the soil and the microgreens have grown, you can tip the tray at almost any angle, and the soil won't fall out.

Soil grows microgreens so much better than any mat or hydroponic system. It's worth the effort to grow microgreens in soil. 

We will do a podcast and write an article on this topic soon. 

Will I get bugs using soil?

We can't say 100% no, but for most microgreens varieties, the plants are harvested before gnats can become a problem. 

Here's how to reduce or eliminate the possibility of having fungus gnats affect the soil. Buy a "fresh" bag professional-grade potting mix. By fresh, we mean soil in recently packaged bags. All commercial potting mix is sterilized before being packaged. There are holes in the bags to allow moisture exchange with the soil, so if potting mixes sit too long on the shelves of a store (especially stores that sell soil near their tropical plants), fungus gnats can lay eggs in the bagged soil.

Ask for new bags and don't buy so much that it sits around in the house. 

The second helpful tip is to not overwater any of your plants, including your houseplants. Fungus gnats only occur when very moist soil is available to the insects for an extended period.

Another insect problem is aphids. I'm not sure how they get in, whether it's from open windows, or they're brought in from outside on shoes or clothes, but they can infest herb microgreens at times. Especially basil and cilantro. The best way to get rid of aphids is to wash them off the microgreens after you harvest them. Short term microgreens like broccoli, radishes, kohlrabi, kale, etc. never have pest problems. 

What do I do with the soil once I've harvested?

We recommend using soil only once. Here are some of the reasons why.

  • It's hard to plant new seeds in the stubble of the old microgreens.
  • Disease issues (damping-off disease) increase significantly with re-use. Even other food-related diseases can form on re-used soil.
  • Insects like Fungus Gnats can become a problem.
  • Much of the available soil nutrients are used up in the first batch of microgreens.

The best use for used microgreen soil is to add it to your compost pile or garden, or a friends compost pile!

You can also start a vermiculture bin, worms are fun!

Spread the soil and roots on the lawn, the soil and roots will disappear into the grass and act as a top dressing to the soil.

We will repeat this because it's the most common question. Re-using the soil isn't wise. We don't even recommend using compost for microgreens. Use only sterile potting mixes.

The chance for a disease related issue is too high using used soil.

Isn't hydroponics better than soil?

Not in our opinion. Seeds grow in soil, as should microgreens. Hydroponics requires the use of chemical fertilizer for maximum microgreen growth. Why use them?

Increasing moisture levels have a higher chance of harmful bacteria blooms. We aren't saying that soil doesn't also run this risk, but harvesting microgreens correctly with soil significantly reduces the contact with bacteria.

We tried growing microgreens hydroponically as well as growing microgreens on pads or fabric, we were not a fan. If you take a tray of microgreens grown on soil and a tray of microgreens grown on fabric or grown hydroponically and smell them, we believe you will choose the tray grown on soil. The other will smell mildewy or moldy most of the time. 

Yes, that's our opinion, and we're sticking to it. Soil is best.

Do I need grow lights?

Absolutely not.

Grow lights are not necessary to grow microgreens. Microgreens will grow well under inexpensive LED lights with a color temperature above 5,000K.

Some microgreens with red leaf color will present themselves better with grow lights, that is they become more red. But they will grow to the same size and density under standard LED lights.

You can, in fact, get by with a southern exposed window sill. But providing artificial light will increase yield and produce a more uniform tray of microgreens.

We have tested and published several articles on microgreen lights.

Some of the lights we recommend can be found on our Resource Page.

When do I take my microgreens out of the blackout period?

A tricky question. I hate to say it depends, but it's true. The general answer is when the root hairs disappear; and you can see stems on the plants, such as those shown below.

best soil for microgreens coir on day 4

For those microgreens under a blackout dome, wait until the plants reach the top of the dome.

Microgreens such as black oil sunflower and peas, go from a weighted blackout once the weight is pushed up and to the side, and then placed in a blackout dome for a couple of more days.

For more specifics, search Home Microgreens for the variety you wish to grow and see the photos included in the article. 

What soil should I use? Can I get it at the garden center?

We recommend using professional coconut coir based potting mix. Such as the mix we make and sell in the Home Microgreens Store.  Make sure its a mix and not pure coconut coir. Pure coir doesn't have the nutrients to grow great microgreens without adding fertilizer. 

We continue to do testing on the most common soil mixes found in the box stores (in fact, we will do a whole series on that) and garden centers. We will have a link to these posts on the home page or on the sidebar to the right of the articles. 

If you don't want to purchase soil from the Home Microgreens Store, we recommend Fox Farms Coco Loco or their Happy Frog mix. Also, Royal Gold Tupur Mix or Basement mix. These can be found at Hydroponic shops. Links to these soils can be found on our Resource Page.

Will my microgreens grow back?

Most microgreens will not grow back. If they do, the growth is slow, and the yield is reduced. It's best to recycle and compost the soil and start fresh.

However, some microgreens, especially the herbs & lettuce, will grow back in what we call "cut and come again." These include onions & leeks, lettuce, celery, peas, and a few others. Harvesting must be completed with care, though.

How much seed should I use?

The amount of seed you should use is calculated by the area of your planting tray and the variety of microgreen you are growing. 

We have developed a seed calculator that will help you narrow down how much seed to use.

Click this link to go to the article containing the seed calculator.

Where can I buy seed and soil?

The Home Microgreens Store, of course!

We have pre-measured seed packets for the Home Microgreens Tray, and 5 by 5, 10 by 10 trays. You can also buy seed by the ounce for most varieties.

Our seeds and supplies are inexpensive, and we offer quick and excellent service. Check out the Home Microgreens Store.

Have a Question? Ask Below

Home Microgreens Also Offers the Following

Microgreen eBook

A comprehensive microgreen ebook that details the principals of growing microgreens at home. Several different methods and processes are detailed.

The ebook comes in two versions, one version includes instructions to grow the most commonly grown microgreens. The second includes access the microgreen vault, a database containing more varieties and information with images taken throughout the stages of growth.

Video Courses for the Home Grower

The Home Microgreens Video Course is perfect for the person that wants to grow one or more trays of microgreens for home use. Trays of microgreens also make great gifts! 

The course includes short, easy to follow videos and checklist for each step along the way.

Step-by-step video instructions are included for the most commonly grown microgreen varieties. 

Grow for Profit Course

Do you want to learn how to grow microgreens for profit? Grow microgreens as a side hustle, retirement income, or maybe even as an occupation. 

It's possible to earn a few hundred to thousands of dollars a month. 

The Grow for Profit Video Course shows you what is involved to set up a microgreens business, how to setup your grow area, and instructions on how to grow many different varieties. 

The Home Microgreens Store

The Home Microgreen Store has all the supplies you need to grow microgreens at home. 

We stock complete microgreen kits, trays, professional potting soil, miscellaneous equipment and of course microgreens seeds.

Microgreen kits make great gifts, home school or rainy day projects, and are fun for the whole family.

Instructions are included as well as email support.

Our kit and seed prices are very competitive if not the lowest on the internet.