How to Grow Microgreens Hydroponically (Seed to Harvest in 10 Days)

Quick Overview

Microgreens are the fastest and easiest crop in hydroponics. From seed to harvest in 7 to 14 days, they require minimal equipment, almost no space, and no advanced nutrients. You grow them on a simple moist mat or thin layer of growing medium, and harvest the entire tray at once by cutting the stems just above the root line. They are packed with concentrated nutrition and intense flavor.

What you will learn:

• Which microgreen varieties are easiest and most rewarding
• How to set up a simple tray for hydroponic microgreens
• Watering, light, and nutrient basics
• When and how to harvest for the best flavor and nutrition
• Troubleshooting mold, uneven growth, and other issues

Best Varieties for Hydroponics

Starter recommendation: Sunflower and radish microgreens are the easiest to grow and the most forgiving of beginner mistakes. Start with these before moving to slower or more finicky varieties.

Getting Started

Germination

1. Soak larger seeds (sunflower, pea) in water for 8 - 12 hours before planting. Smaller seeds (radish, broccoli, arugula) do not need soaking.
2. Lay a growing mat (hemp, coconut coir, or jute) in a shallow tray. Moisten the mat thoroughly with plain water or very dilute nutrient solution.
3. Spread seeds densely and evenly across the mat. Microgreens are planted much more thickly than regular crops. Seeds should be close together but not stacked on top of each other.
4. Cover the tray with another tray or a sheet of cardboard for 2 - 4 days (the blackout period). This forces the seeds to push upward and develop strong stems.
5. Keep the mat moist during blackout by misting or bottom-watering once or twice daily.

After Blackout

1. Remove the cover after 2 - 4 days when sprouts are about 1 - 2 inches tall.
2. Move the tray under light. Microgreens will be pale yellow at this stage and will green up quickly.
3. Continue watering by misting or bottom-watering to keep the mat moist but not soaking.

Tip: Bottom-watering (pouring water into a tray beneath the growing tray) produces cleaner microgreens with less mold risk than top-watering or misting.

Nutrient Requirements

Nutrient type: Most microgreens grow perfectly well on plain water alone since the seed provides all the nutrition for the short growing cycle. If you want slightly faster or more robust growth, add hydroponic nutrient solution at one-quarter strength after the blackout period. Do not use full-strength nutrients on microgreens.

Water temperature: Room temperature water (65 - 75 F) is fine. Microgreens are not fussy about water temperature.

Light Requirements

• Minimum: 8 - 12 hours of moderate light per day after blackout.
• Ideal: 12 - 16 hours under any grow light or on a bright windowsill.
• Intensity: Microgreens do not need intense light. A basic LED shop light, T5 fluorescent, or even a sunny windowsill is sufficient. Position lights 4 - 8 inches above the tray.
• During blackout: No light. Keep the tray covered for the first 2 - 4 days.

Common Problems

Harvesting

When to Harvest

Harvest microgreens when the first set of true leaves has fully opened, typically 7 to 14 days after planting depending on the variety. At this stage, the stems are 1 - 3 inches tall and the cotyledon leaves (the first pair) are fully expanded.

How to Harvest

Use clean, sharp scissors or a knife to cut the stems just above the growing mat. Cut the entire tray at once. Microgreens do not regrow after cutting, so each tray is a single harvest.

Storage

• Harvest just before eating for the best flavor and nutrition.
• If storing, place dry microgreens (do not wash until ready to eat) in a sealed container lined with a paper towel in the refrigerator.
• They stay fresh for 5 - 7 days when stored properly.
• Immediately after harvest, compost the used mat and remaining root mass, sanitize the tray, and start a new batch.

Recommended Systems and Plans

For beginners (minimal setup):

• Kratky Windowsill Microgreens -- The simplest possible microgreen setup. A tray, a mat, and a windowsill.
• Kratky Mason Jar Herb Garden -- Adapt this simple jar setup for a single small batch of microgreens.

For regular production:

• Kratky Balcony Salad Garden -- Use multiple trays alongside greens for a full salad garden.
• NFT Microgreens Rack -- A multi-tier rack system designed specifically for continuous microgreen production.
• NFT Tabletop Lettuce Farm -- NFT channels can be adapted for tray-based microgreen growing.

Frequently Asked Questions

Do microgreens need hydroponic nutrients?

Most microgreens grow perfectly well on plain water alone. The seed itself contains all the energy and nutrition the plant needs for the 7 to 14 day growing cycle. Adding a very dilute hydroponic nutrient solution (one-quarter strength, EC 0.2 to 0.5) after the blackout period can produce slightly taller and more robust greens, but it is optional. Many experienced microgreen growers never use nutrients at all. Keep it simple, especially when starting out.

What is the blackout period and why is it important?

The blackout period is the first 2 to 4 days after planting when you cover the microgreen tray with a lid or another tray to block all light. This forces the seedlings to stretch upward searching for light, which produces longer, more tender stems. Without a blackout period, microgreens tend to grow short and squat with less stem to harvest. The weight of the cover tray also provides gentle pressure that helps seeds make firm contact with the growing mat for better germination.

How many times can you harvest microgreens from one tray?

Microgreens are a one-harvest crop. Once you cut the stems above the mat, they will not regrow because the growing point has been removed. After harvest, compost the root mat, sanitize the tray with dilute hydrogen peroxide or vinegar, and start a fresh batch with new seeds. Most growers run multiple trays staggered by a few days so they always have a tray ready to harvest. With a 7 to 10 day cycle, you can produce 3 to 4 harvests per month from each tray position.

Are hydroponic microgreens more nutritious than mature vegetables?

Research has shown that microgreens can contain 4 to 40 times more concentrated nutrients than their mature vegetable counterparts, depending on the variety. Broccoli microgreens are especially notable for their high sulforaphane content. However, you eat much smaller quantities of microgreens compared to full-size vegetables, so they work best as a nutrient-dense addition to your diet rather than a replacement for larger servings of mature produce. Growing them hydroponically at home ensures maximum freshness and nutrient retention since they go from tray to plate in minutes.