Germinating Difficult Seeds

Germinating Difficult Seeds

Special techniques for nature’s toughest seed coats

Not all seeds are ready to sprout the moment they hit the soil. Some—like pawpaw, caper, sea buckthorn, Strelitzia, and jujube—have evolved thick shells or internal dormancy that must be broken before they’ll grow. This guide covers the advanced techniques needed to germinate these types of seeds successfully.

🛠️ Scarification

Some seeds have extremely hard outer shells that repel water and oxygen. Scarification is the process of weakening that barrier so the seed can absorb moisture and begin germination.

How to Scarify:

  • Manual sanding: Rub each seed on medium-grit sandpaper (80–120 grit) until you see a dull patch—but stop before you see white!
  • Nicking: Use a sharp knife or scalpel to make a shallow cut on the seed coat.
  • Rock tumbler method: Add cut-up sandpaper pieces into a rock tumbler drum along with 5–15 seeds. Tumble dry in 10-minute bursts, checking often. Look for a dull patch—not exposed white tissue.

🔍 Tip: Strelitzia seeds benefit most from gentle abrasion followed by warm soaking. Don't overdo it!

❄️ Cold Stratification

Seeds like pawpaw, caper, and sea buckthorn need to experience a period of cold to break internal dormancy. This mimics natural winter conditions.  Cold Stratification requires that seeds be moist and cold, think wet ground over winter.

Methods:

  • Paper Towel Method: Wrap seeds in a damp (not wet) paper towel, seal in a labelled ziplock bag, and place in the fridge (not freezer). Keep an eye on the seeds during stratification — a little surface mold is okay, but you want to avoid slimy mold or rot. If that starts to appear, gently rinse the seeds, replace the paper towel, and pop them back in.  This works best for small seeds like capers, so you don’t lose them in sand.
  • Sand or perlite method: Mix seeds with sterile, moist sand or perlite in a labelled bag or sealed container and refrigerate. Check often for mold. Great for medium to large seeds like sea buckthorn.
  • Sphagnum moss method: Place seeds in barely damp sphagnum moss in a vented container.  Great for large seeds like pawpaw.

🧊 Tip: Use an anti-fungal like cinnamon powder or a fungicide such as Captan to protect seeds during long stratification. Lightly dust the seeds before placing them in moist media to help prevent mold and rot.

Stratification usually takes 60–120 days at 4–5°C depending on the seeds. Check monthly to ensure no mold or drying out.

🧊 Tip: Label and date your bag! It helps with tracking progress.

🧪 Gibberellic Acid (GA₃) Treatment

Some seeds can bypass stratification altogether by using gibberellic acid (GA₃), a natural plant hormone that tells the seed, “it’s time to grow.”

When to Use GA₃:

  • Strelitzia: After scarification and 24-hour warm water soak, soak in GA₃ at 250–500 ppm for 24 hours.
  • Pawpaw: Apply GA₃ after 90+ days of cold stratification to boost germination speed.
  • Capers, Sea Buckthorn, Jujube: GA₃ at 300–500 ppm for 24–48 hours can significantly improve germination rates.

Click here to purchase Gibberellic Acid (GA₃)

🌱 Sowing & Heat

Once pre-treatment is complete, it’s time to plant!

Best Practices for Tricky Seeds:

  • Use a free-draining seed-starting mix, or a blend of seed mix and coarse sand.
  • Plant seeds to a depth about 2–3x their diameter.
  • Use a heat mat set to 20–30°C to maintain consistent warmth.
  • Cover trays with clear humidity domes or plastic to retain moisture.
  • Label each batch clearly — especially for seeds that may take weeks to sprout.

🌡️ Tip: Strelitzia and pawpaw especially benefit from warm bottom heat and consistent moisture.

🔆 Light-Dependent Germination

Some seeds will not germinate if they’re buried, as they rely on light exposure to signal that conditions are safe for sprouting. Seeds such as Shiso (Perilla), Culantro, Henna, Epazote, and Lithops all require light for successful germination.

Directions:

  • Surface-sow the seeds directly onto the soil and press gently to ensure contact without covering them.
  • Use a fine mist of water so the seeds stay on the surface instead of sinking below the mix.
  • Maintain even surface moisture using a humidity dome, vented lid, or cling film to slow evaporation.
  • Provide bright indirect natural light (sunny windowsill or greenhouse bench) or artificial grow lights positioned 10–20 cm above the tray.
  • Aim for 12–16 hours of consistent light daily for best germination results.

💡 Tip: Light-sensitive seeds dry out quickly — check daily and mist as needed.

✨ Patience & Observation

Difficult seeds can take weeks, months or years to germinate. Germination may be staggered, so don’t discard trays too soon.

With the right prep, even the toughest seeds will reward you with vigorous, unique plants that were worth the wait.

Back to blog