How to grow mustard microgreens
Overview
Mustard microgreens are the young seedlings of Brassica juncea, harvested at the cotyledon or first true leaf stage for their spicy, peppery flavour. They are a fast, dense crop grown in trays or beds, and require consistent moisture and good airflow to avoid damping off.
Varieties
- Red Giant — A fast-growing mustard with deep purple-red leaves and a strong, spicy flavour; popular for colour contrast in mixes.
- Mizuna — A mild, feathery-leafed mustard that is slightly less pungent than standard mustard; good for beginners.
Soil Preparation
Use a fine, sterile seed-raising mix or a 50:50 blend of coir and compost. Aim for a pH of 6.0–7.0. Ensure the mix is light and well-draining; heavy garden soil will cause compaction and poor germination.
Growing Guide
Sow seed thickly (about 10–15 g per 30×40 cm tray) on a moistened seed-raising mix, then cover lightly with vermiculite or a thin layer of mix. Keep in bright, indirect light (part shade) and maintain even moisture by misting or bottom-watering; avoid overhead watering that can splash soil and cause disease. Germination takes 2–4 days; harvest at 7–14 days when 5–8 cm tall. For a continuous supply, sow a new tray every 5–7 days.
Sowing
Sow seed directly on the surface of moistened mix, then cover with a thin layer (2–3 mm) of vermiculite or fine mix. Do not bury deeply; seeds need light to germinate. Germination occurs in 2–4 days at 15–25°C. Direct sow only; transplanting is not practical for microgreens.
Care
No pruning or training is needed. Feed with a very dilute liquid seaweed or fish fertiliser once after germination (at half strength) to boost leaf growth. Remove any yellowing or mouldy leaves immediately to maintain airflow and prevent rot.
Companion Planting
Mustard microgreens are usually grown alone in trays, but in a garden bed they suit beetroot, lettuce, and radish. Avoid planting near other brassicas (broccoli, kale, cabbage) if you want to prevent cross-contamination of pests or diseases.
Common Pests & Risks
Damping off (caused by overwatering or poor airflow) is the main risk; use sterile seed-raising mix and avoid waterlogging. Fungus gnats can appear if soil stays wet; let the surface dry slightly between waterings. Aphids may attack if left too long; spray with a weak soap solution if needed.
Harvesting
Harvest when the first true leaves appear (or at cotyledon stage for extra spice), using clean scissors to cut just above the soil line. The crop is ready 7–14 days after sowing; harvest in the morning for best crispness. Rinse gently and use immediately or store in a sealed container in the fridge for up to 3 days.
In the Kitchen
Use fresh in salads, sandwiches, or as a garnish for soups and stir-fries. The spicy kick comes from glucosinolates; add at the end of cooking to preserve flavour. Store in a damp paper towel in a sealed bag in the fridge for up to 3 days.
Troubleshooting
Yellow leaves: usually from overwatering or poor drainage; reduce watering and improve airflow. Leggy growth: caused by insufficient light; move to a brighter spot or use a grow light. Mould on surface: from too much moisture; increase ventilation and water from below. Slow germination: seed too old or soil too cold; use fresh seed and keep at 18–25°C. Bitter taste: from letting plants grow too long; harvest at 7–14 days for best flavour.