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Seed Compost Basics

Martha Stewart Living Television

If you're having trouble starting plants by seed, it might not be the seeds that are the problem but the mix you planted them in. Experimenting with ingredients and proportions allows you to provide the mixture that best meets your plants' needs.

With just three ingredients, Dan Hinkley, of Heronswood Nursery in Kingston, Washington, makes an all-purpose seed compost for even the fussiest perennials and shrubs, including firethorn (Pyracantha) and Pernettya (sometimes known as Gaultheria). He uses sand and perlite to improve drainage and aeration; peat to improve the mixture's ability to retain air and water by increasing the amount of pore space; and, in small amounts, superphosphate and dolomitic lime, which act as nutrients and pH balancers.

Seed Compost Basics

Tools and Materials

  • Bucket
  • 1 part coarse sand
  • 1 part perlite
  • 1 part peat
  • 1 tablespoon superphosphate
  • 1 tablespoon dolomitic lime
  • Dust mask

Seed Compost How-To
1. Measure and add all the ingredients to the bucket.

2. Lightly moisten the materials before mixing them to help hold down the dust and bind the ingredients together -- but don't soak the mixture or you'll make a muddy mess.

3. To protect yourself from airborne dust, wear a mask. Carefully toss the ingredients to ensure that pockets of materials are not left unincorporated.

Sowing Seeds

You can get your seeds from a local nursery or directly from the plant, like Dan does. To prepare firethorn seeds for sowing, first separate the flesh from the seeds. Put the small fruit into a blender with a plastic dough blade, cover the seeds with water, and lightly pulse. Decant the seeds into measuring cups; the good seeds will fall to the bottom, while the bad seeds and fruit will rise to the top. Turn the seeds out onto paper towels.

To prepare the smaller Pernettya for sowing, place fruits between paper towels and roll out with a rolling pin. Let the seeds dry, then scrape them off the paper towel.

Tools and Materials

  • Plastic container (or sterilized plastic salad containers with drainage holes punched in the bottom)
  • Seed-compost mix (recipe above)
  • Soil tamper
  • Spray bottle
  • Grit or peat for topdressing

Sowing Seeds How-To
1. Fill a clean and sterile plastic container 2/3 of the way with prepared seed-compost mix. Tamp the mix down, then continue adding and gently tamping until the mix is about 1/2 inch from the top.

2. The rule of thumb is to plant seeds twice as deep as the seed's size. Use your finger or a pencil to make shallow holes, put in the seeds, and cover lightly. Plant larger seeds no more than 1 inch apart and 1 inch deep, and medium seeds a 1/2 inch apart and a 1/2 inch deep. The smallest seeds should be thinly scattered on the surface -- make furrows with a pencil or ruler -- --and very lightly covered. Some seeds should not be covered at all because they need light to germinate; the packets will tell you which.

3. Label the pot with the plant's name and sowing date. Moisten soil using a spray bottle; be gentle so you don't wash the seeds away, and always use room-temperature water. Topdress with grit, up to 1/4 inch, or peat if the seed is acid loving.

Resources
For more information about Heronswood Nursery, visit heronswood.com Learn more about plants from Dan's book "The Explorer's Garden: Rare and Unusual Perennials."