March 2024: Making Soil for Seeds

The rain in February flooded the areas around the garden beds in the Edible Demo Garden. Volunteers were busy digging trenches to redirect the water away from the planted areas and salvaging any crops that were still productive. The wind also created havoc, blowing over compost bins, scattering planting containers, and overturning a picnic table. Once the damage was mitigated, there was little that could be done in the garden itself until the water drained and the soil began to dry. Attempting to work in soggy soil can create future problems due to soil compaction.

However, the Edible Demo Garden volunteers are not a group to remain idle, especially when it’s time to start seedlings for the spring and summer garden. The organic seeds for the chosen crops had arrived and they needed to be planted in the proper soil mixture and placed in the greenhouse to germinate. So, on a rare dry day, an enthusiastic group of volunteers met to make soil for growing seedlings.

What soil is best for starting seeds?

While some plants such as carrots, grow better when they are directly seeded into the garden, many others benefit from earlier starts in more protected conditions and are transplanted later into the garden. In the Edible Demo Garden, any soil used to start plants from seeds must be organic, containing no synthetic materials. Due to the amount of soil needed, it’s much more economical to make the seedling mix rather than purchase a ready-made organic mix. There are many recipes for seeding mixes, but most important is that they are formulated to hold air and moisture and are free of harmful bacteria. There are two soil mix recipes developed for the Indian Valley Organic Farm and Garden and these are also used in the Edible Demo Garden. Labeled “Breakfast Mix” and “Lunch Mix”, they are made by hand and shovel in large quantities. Screen tables set over plastic tarps are used for the sifting.

Breakfast Mix

Breakfast mix is used for starting seeds in trays or flats. It is made by sifting together the following materials:

• 4 wheelbarrows Lunch Mix (20 cubic ft., already sifted)
• 1 bag Vermiculite (4 cubic ft.) (medium or fine)
• 1 bag Peat Moss (4 cubic ft.)

Lunch Mix

Lunch mix is used for potting up seedlings prior to transplanting or for bigger plants that will remain in 1–3-gallon containers for several months or more. The recipe for lunch mix is as follows. All the ingredients are mixed thoroughly and sifted together.

• 6 wheelbarrows sifted compost
• 1 bag Peat Moss (4 cubic ft.) 
• 1 bag Vermiculite (4 cubic ft.) (medium or fine)
• 1 bag Perlite (4 cubic ft.) (medium or fine)
• 10 lbs or 6 qt Azomite (micronized)
• 5 lbs or 5 qt Feather Meal (fine)
• 2.5 lbs or 2 qt Kelp Meal (fine)

What is the purpose of the ingredients in a seedling mix?

Any mix must meet the needs of plant roots for air, water, nutrients, and support.

• Compost – adds structure, provides nutrients, and contains beneficial microbes
• Peat moss – retains moisture (coconut coir is considered a sustainable alternative)
• Vermiculite – mined mineral, increases soil porosity and adds calcium and magnesium
• Perlite – light, volcanic rock, helps to aerate by increasing pore space
• Azomite – adds trace minerals
• Feather meal – releases nitrogen
• Kelp meal – adds nitrogen, potassium, and phosphorus

Ready to plant

Once the “breakfast mix’ was made, it was used to fill seeding trays and planting could begin. A light topping of vermiculite was added to each cell to maintain the right moisture level.

Click on the following for more information on soil mixes and starting plants from seed: 

Sowing seeds for fun, flavor, and a successful harvest

Build healthy soil