Seedling Mix - Seed Starting Soil

Start Seeds Right the First Time

Here's the thing about starting seeds—most failures happen because people use regular potting soil. It's too heavy, too dense, and often way too rich for delicate seedlings. Seeds need something lighter and fluffier that they can actually push through.

This seedling mix is formulated specifically for germination. It's light enough for tiny seeds to sprout through, airy enough so seedling roots don't suffocate, and gentle enough that you won't burn tender new growth. Plus it's got Ancient Soil in it, which means beneficial microbes that protect against damping off—that awful fungal disease that kills whole trays of seedlings overnight.

You'll get better germination rates, stronger root systems, and seedlings that actually handle transplanting without wilting dramatically. Start your garden off right instead of having to redo everything three weeks in.

Why Seeds Need Different Soil

Seeds and seedlings have completely different needs than established plants. When a seed germinates, it's living off stored energy in the seed itself. That tiny emerging root is delicate—it needs to push through the soil easily without hitting obstacles. And once it sprouts, the seedling needs air circulation around its roots or it'll rot.

Regular potting soil is formulated for mature plants with developed root systems. It's too dense for seeds. The texture can crust over on top, trapping seeds underneath. And it often contains too much nutrition, which can actually burn seedling roots that aren't ready for it yet.

Seedling mix is finer, lighter, and fluffier. Water drains through it while still keeping things moist. Delicate roots can spread easily. And the nutrition level is gentle enough for brand-new plants.

What's in This Mix

How to Use Seedling Mix

The Damping Off Problem

If you've started seeds before, you've probably dealt with damping off. One day your seedlings look fine, the next morning they're flopped over at the soil line with a pinched, rotted stem. It's caused by fungi (usually Pythium or Rhizoctonia) that thrive in wet, warm conditions—exactly the environment seeds need to germinate.

Most seed starting mixes are sterile to avoid this, but sterile just means there's nothing bad AND nothing good. When pathogenic fungi do show up (and they will, from the air or water or your hands), there's nothing to stop them.

This mix takes a different approach. The beneficial microbes in Ancient Soil colonize around seedling roots and outcompete the bad fungi. They create a protective barrier during that vulnerable period right after germination. Combined with the mix's good drainage (fungi love waterlogged soil), you get way better seedling survival.

You can't completely eliminate damping off—the fungi are everywhere—but you can stack the odds in your favor with good mix, proper watering, and air circulation.

When to Transplant

Seedlings are ready to transplant when they've developed 2-4 true leaves (not counting the first cotyledon leaves that emerge) and are about 2-3 inches tall. They should have visible roots coming out the bottom of the cell or starting to circle the sides.

Don't wait too long. Once seedlings outgrow their space, growth slows down and they get leggy and weak. But also don't transplant too early—wait until they're sturdy enough to handle the move.

Most seedlings can stay in this mix for 4-8 weeks. Fast growers like tomatoes and cucumbers will be ready on the early side. Slower stuff like peppers might take longer. The plants will tell you—when growth noticeably slows despite good conditions, it's time to move them.

What Seeds Work Best

Vegetables

Pretty much all vegetable seeds do great in this mix. Tomatoes, peppers, eggplant, cucumbers, squash, melons, lettuce, kale, broccoli, cabbage—everything. Heat-loving stuff like tomatoes and peppers germinate faster with a heat mat underneath, but the mix works either way.

Herbs

Basil, parsley, cilantro, dill, oregano, thyme—all the common herbs start well in this mix. Basil is notoriously prone to damping off, so the beneficial microbes really help. Parsley is slow (2-3 weeks to germinate), but it'll get there.

Flowers

Annual flowers like zinnias, marigolds, cosmos, and sunflowers are super easy in this mix. Perennials work too, though many take longer to germinate. If you're starting petunias or other tiny-seeded flowers, just barely press them into the surface—they often need light to germinate.

Microgreens

The mix works well for microgreens if you're harvesting them young. Spread seeds densely on the surface, cover lightly, keep moist. They'll be ready to cut in 1-2 weeks depending on variety.

Common Seed Starting Mistakes

Planting Too Deep

This kills more seeds than anything else. Tiny seeds like lettuce or basil barely need covering—just press them into the surface. Bigger seeds like beans or squash can go deeper. When in doubt, plant about 2-3 times as deep as the seed is wide.

Not Enough Light

Once seedlings emerge, they need bright light—like, a lot of it. A sunny windowsill often isn't enough. Seedlings stretch toward light and get leggy and weak. If you don't have a super bright window, use a grow light. Keep it 2-4 inches above seedlings and leave it on 14-16 hours daily.

Overwatering

Keep the mix consistently moist, not soaking wet. Overwatering is the main cause of damping off and root rot. The surface can dry slightly between waterings once seedlings are established—just don't let them wilt.

Starting Too Early

There's a tendency to start seeds way too early because you're excited. But if you start tomatoes in January and can't transplant outside until May, you'll have massive root-bound plants that struggle when finally planted. Check your last frost date and count backward based on seed packet timing.

Forgetting to Harden Off

Seedlings grown indoors are soft and pampered. You can't just stick them directly in the garden. They need to be hardened off—gradually exposed to outdoor conditions over 7-10 days. Start with a few hours of shade, gradually increase sun and outdoor time. Otherwise they'll get scorched or stressed.

How Much Do You Need?

A little goes a long way with seed starting. A 3-quart bag of Seedling Mix will fill:

• About 4-6 standard 72-cell seed starting trays
• Or 50-60 individual 3-inch pots
• Or 2-3 standard 1020 seed flats if you're broadcasting seeds densely

Most home gardeners can start a whole season's worth of seedlings with one bag. If you're starting hundreds of plants or doing multiple successions, grab a couple bags.

Watering Tips for Seedlings

Watering seedlings is tricky—they need consistent moisture but hate being waterlogged. Here's what works:

• Before germination: Keep consistently moist. Check daily. Some people cover trays with plastic domes or plastic wrap to maintain humidity.
• After germination: Remove any covers immediately. Let the top of the mix dry slightly between waterings, but don't let seedlings wilt.
• Bottom watering: Set trays in shallow water for 10-20 minutes until surface looks moist, then drain. Less risk of disturbing seedlings or encouraging surface fungi.
• Top watering: Use a gentle spray or watering can with a fine rose. Water until it drains from the bottom. Avoid blasting seedlings with a strong stream.

Why This Mix Works Better

We tested this mix against basic seed starting mixes and regular potting soil. The results were pretty clear:

• Better germination rates: Especially for finicky seeds like parsley and peppers
• Less damping off: The beneficial microbes make a real difference
• Stronger root systems: Seedlings develop more extensive roots in the light, airy texture
• Better transplant survival: The Ancient Soil seems to help seedlings handle the stress of transplanting
• Healthier overall growth: Seedlings just look more vigorous—deeper green, sturdier stems

The difference is most obvious with seeds that are prone to problems—like basil (damping off) or peppers (slow germination). But even easy stuff like tomatoes and zinnias just performs better.

Storage

Keep unused mix in the bag, sealed, in a cool dry place. It'll stay good for years. The microbial life goes dormant when dry and wakes back up when moistened. Even if it's been sitting for a while, it'll work fine—just mix it up a bit before using.

Don't reuse mix from previous seasons for seed starting. The structure breaks down, nutrients are depleted, and it might harbor pathogens. Add used mix to garden beds or compost bins. Fresh mix each season gives you the best shot at success.

Common Questions About Seedling Mix