Tomato and pepper seeds started indoors need a light soilless mix, and a bag made for seed starting is the easiest way to get one. Start with Miracle-Gro Indoor Potting Mix for Seed Starting, which is ready to use.
Miracle-Gro says one 8 qt bag fills three 72-cell trays, which lets you count trays before you buy.
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The five mixes, at a glance:
- Miracle-Gro Indoor Potting Mix for Seed Starting, 2-pack: ready to use, for cell trays.
- Hoffman Seed Starter Potting & Planting Mix: a soilless mix with a wetting agent.
- Burpee Organic Coconut Coir Seed Starting Mix: dry coir bricks that expand when wetted.
- Jiffy Natural & Organic Seed Starting Mix: peat moss, vermiculite and lime.
- Purple Cow Seed Starter Mix: compost-based, with feed built in.
Miracle-Gro Indoor Potting Mix for Seed Starting, 8 qt, 2-pack
A first tray of tomato and pepper seeds, with no mixing to do.
Miracle-Gro Seed Starting Potting Mix, 8 qt, 2-Pack
Ready to use in cell trays
Maker says one bag fills three 72-cell trays
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The mix is enriched with plant food. It contains no compost or bark, which the maker says shelter fungus gnats.
On that figure, the 2-pack fills about six 72-cell trays. Exact amounts may vary.
- Works well for
- A bag size you can turn into a tray count
- Not needed if
- One small tray of seeds (the pack is two 8 qt bags)
Hoffman Seed Starter Potting & Planting Mix, 10 qt
Seeds in trays or cells where the mix needs to take up water.
Hoffman Seed Starter Mix with Wetting Agent, 10 qt
Soilless mix, six components
Wetting agent for moisture retention
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This is a light, loose, fertile soilless mix for germination, with a wetting agent (an additive that helps a mix soak up water).
It is also sold for transplanting and root cuttings, so leftover mix has a second use once the seedlings are up.
- Works well for
- A mix that also suits transplanting and root cuttings
Burpee Organic Coconut Coir Seed Starting Mix, 16 qt
A peat-free mix that stays flat and dry in a drawer until you are ready to sow.
Burpee Organic Coconut Coir Seed Starting Mix, 16 qt
Coir (coconut husk fiber) bricks
Each brick expands into 8 quarts
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The coir is a renewable alternative to peat moss, made from recycled coconut husks.
Each brick expands into 8 quarts of mix once water is added, which makes 16 quarts in total. The bricks take up little space until planting day.
Jiffy Natural & Organic Seed Starting Mix, 10 qt
A plain three-ingredient mix with a short ingredient list you can read at a glance.
Jiffy Natural & Organic Seed Starting Mix, 10 qt
Peat moss, vermiculite and lime
10 qt bag
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The mix is peat moss, vermiculite and lime. Vermiculite (a moisture-holding additive) helps prevent compaction.
The lime is there to balance pH, which is how acidic the mix is.
Purple Cow Seed Starter Mix, 12 qt
Seedlings you want fed by a compost-based mix, which the maker rates for up to 45 days.
Purple Cow Seed Starter Mix, 12 qt
Compost-based, ready to use
Fertility for up to 45 days per the maker
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The mix is made with the maker’s own activated compost and has everything needed to start seeds.
It carries enough fertility for up to 45 days, per the maker.
- Works well for
- Compost-based mix with feed already in it
Seed mix and potting mix are not the same
Seed mix has a finer texture, and garden soil is too dense for a tray.
University of Maryland Extension says special seed starter media have a finer texture, which helps germinate very small seeds. It adds that true soil is too dense to allow good air and water movement.
Wet the mix before it goes into the cells
Moisten the mix first, until it feels like a wrung-out sponge. Thoroughly moisten dry media before filling pots. That matters most if it contains peat moss, as most potting mixes do.
The test is a mix as moist as a wrung-out sponge, not sopping wet. After sowing, Miracle-Gro says to keep the mix moist and out of direct sunlight until germination.
Why seeds fail in the wrong mix
Damping off, the disease that rots seedling roots, takes hold when the mix stays wet. Water molds named Pythium, Phytophthora and Rhizoctonia cause it.
It can quickly kill a container of seedlings if the growing media is kept too wet. Indoor seedlings succumb to damping off if the media is poorly drained and kept too wet.
The Oregon State University Extension Service, which answers questions from the public through Ask Extension, has a warning too. Backyard soil is compacted, full of weed seeds and not pasteurized, which can lead to seedling diseases.
The way to prevent it is a well-drained mix and less frequent watering. Allow the top of the growing mix to dry slightly before watering. Soilless potting media are also recommended for growing transplants.
Buy it or make it
A bag of seed mix saves the pasteurizing step; the homemade recipe needs it. Oregon State’s recipe is three equal parts:
- One-third pasteurized soil or compost.
- One-third sand, vermiculite or perlite.
- One-third coconut coir or peat moss.
Pasteurizing means heating the soil or compost so it is free of pests and diseases. Oregon State says to keep the mix at 180 degrees for 30 minutes. It warns that overheating damages the soil structure.
| Your pots and space | Start with this |
|---|---|
| A first tray of tomatoes and peppers, no mixing | Miracle-Gro Indoor Potting Mix for Seed Starting, 8 qt, 2-pack |
| Seeds in trays, with a wetting agent in the mix | Hoffman Seed Starter Potting & Planting Mix, 10 qt |
| A peat-free mix stored dry until sowing | Burpee Organic Coconut Coir Seed Starting Mix, 16 qt |
| A short peat, vermiculite and lime mix | Jiffy Natural & Organic Seed Starting Mix, 10 qt |
| Compost-based mix with feed for up to 45 days | Purple Cow Seed Starter Mix, 12 qt |
| An oven, a pasteurized base and time to mix a batch | Homemade mix (Oregon State recipe) |
Which way to go for a first tray
For a first tray, buy a bag. When the tray is filled, a seed-starting schedule by frost date shows which month to sow by your frost date.
The mix for the final pot is a different product. What makes a good potting mix for containers covers its ingredients and reusing it.
Keep the homemade recipe for a year when you already have a pasteurized base.
