The Best Seed Starting Mixes of 2021

Giving flowers and vegetables a head start with seed saves money and offers gardeners a wider selection of plants. To increase your odds for success, use a growing mix designed especially for germinating seeds.

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The Best Seed Starting Mix Options

Photo: amazon.com

Starting plants from seed allows you to grow almost any plant species that can be propagated from seed, rather than choosing from a limited selection of starter vegetables and flowers at nursery centers. When the weather warms, gardeners often head outdoors to sow quick-sprout vegetables, such as cucumbers and squash, but other traditional summer favorites, including tomatoes, need more time to mature before being transplanted in the garden.

Starting seeds indoors is a rewarding, economical way to get a jump on the gardening season, but it can be tricky. An entire flat of tiny seedlings can succumb to fungus or disease without warning or apparent cause. To reduce the risk of seedling failure, use the right medium, an uncontaminated grow mix, instead of any old soil. The best seed-starting mix is clean and lightweight, and it offers an optimal foundation for delicate seedlings to take root. Ahead, learn what to look for when shopping for a seed-starting mix and find out why the quality products detailed here can help gardeners get a jump on the growing season.

  1. BEST OVERALL: Espoma Seed Starter Potting Mix
  2. RUNNER UP: Hoffman Seed Starter Soil
  3. BEST BANG FOR THE BUCK: Miracle-Gro Seed Starting Potting Mix
  4. BEST ORGANIC: Coast of Maine Organic Seed Starter
  5. BEST COCONUT COIR: Burpee Coconut Coir Concentrated Seed Starting Mix
  6. BEST PELLETS: Jiffy Seed Starter Soil Plugs
  7. BEST WINDOW KIT: Window Garden Seed Starting Kit
  8. BEST FOR HYDROPONICS: Urban Leaf AeroGarden Compatible Sponges
  9. ALSO CONSIDER: Sun Gro 8-Quart Seedling Mix
The Best Seed Starting Mix Options

Photo: amazon.com

Before You Buy Seed Starting Mix

Before spring arrives, garden centers begin stocking large bags of growing medium, but don’t grab one without reading the label. Growing mixes come in various blends, some designed to amend outdoor garden beds, while others are for potted plants. Still others contain fertilizers for specific plants, such as “acid-loving” or “indoor.” Along with standard potting soil, most of these options are not suitable for starting seeds because they contain some contaminants. Choose a mix labeled for starting seeds to ensure it doesn’t contain traces of fungus or bacteria that could wipe out tiny seedlings.

What to Consider When Choosing the Best Seed Starting Mix

Most seed-starting mixes are soilless, which means they contain no dirt. While established plants may thrive in real soil, the delicate roots of just-sprouted seeds may find it challenging to expand and dig deep if the soil contains hardened clumps. Moreover, the leaf ends of sprouts (called “cotyledons”) may not be able to push their way to the surface of the soil. Seed-starting mix has a light, airy consistency, so tender roots and sprouts can grow without resistance.

Ingredients

Most seed-starting mixes contain one or more of the following ingredients:

  • Sphagnum peat moss: The most common base ingredient in seed-starting mixes, sphagnum peat moss is the decomposed material of sphagnum moss, a moss that grows in peat bogs. After it’s sterilized and dehydrated, sphagnum peat moss provides an optimal base for seeds to sprout; it’s absorbent yet won’t pack down. Peat moss, also popular for compressing into small pods, is called “peat pellets,” which expand into fluffy grow mix for starting seeds when immersed in water.
  • Coconut coir: Removed from the outside of coconuts during the harvest process, coir is the fibrous layer that surrounds a hard coconut shell. Formerly discarded as a waste product, coir is now valued for its ability to retain moisture without compacting, making it well suited as an ingredient in seed-starting mixes. Like sphagnum peat moss, coir can be dehydrated and compressed into plugs for rehydrating and starting seeds.
  • Perlite: Perlite is a byproduct of volcanic glass that’s been heated to high temperatures, resulting in a product that resembles puffy white beads. Perlite retains a small amount of moisture, but its primary purpose is to keep the growing mix from compacting.
  • Vermiculite: Almost as light as perlite but highly absorbent, vermiculite is a silica mineral that’s mined from the earth. It’s in potting soil and seed-starting mix to lighten the mixture and help retain moisture.
  • Diatomaceous earth (DE): This powdery natural product in some seed-starting mixes helps kill insects. Diatomaceous earth contains the finely ground fossils of tiny aquatic organisms known as “diatoms.” When insects come into contact with DE, the powder sticks to their bodies and acts as a desiccant to dehydrate and kill them.
  • Lime: Powdered lime is in some seed-starting mixes to help lower the pH level of the mix to around 6 to 6.5 on the pH scale. The pH scale ranges from 0 to 14, with 7 considered neutral. Higher numbers indicate greater alkaline content, and lower numbers indicate more acidic content. Most plants grow well in soil with a pH level of around 6.5 to 7.
  • Wetting agent: Completely dry grow mix ingredients initially resist absorbing water, so some manufacturers include a wetting agent (surfactant) that helps the material absorb water. A wetting agent, such as powdered kelp, is needed the first time the material is moistened.

Organic vs. Non-Organic

When a seed-starting mix is labeled “organic,” gardeners know that all its ingredients are natural and contain no chemicals or synthetic agents. Most seed-starting mixes contain most, if not all, natural ingredients, but the inclusion of synthetic fertilizers disqualifies it as organic. An organic seed-starting mix may be more important to those who produce edible vegetables rather than flowers or ornamental plants.

Sterilization

Manufacturers remove fungi and bacteria from seed-starting mix by heating it to over 200 degrees Fahrenheit for a period of time, usually at least 30 minutes, to destroy pathogens that might kill tender seedlings. Depending on the manufacturer, heat may be applied by forcing steam through the material or by submerging the mixture in water and heating the water. Sterilizing the mixture gives delicate seeds their best chance at survival.

Aeration and Moisture Retention

A seed-starting mix should retain its lightness and loft, even when wet. Not only do new roots need moisture to grow, but they also need oxygen. Manufacturers add perlite and vermiculite to aerate the mix. Starting seeds in compact or heavy potting soil usually results in poor germination rates. Optimal seed-starting mixes retain just enough moisture for the mixture to stay damp to the touch while still providing the aeration necessary for roots to develop.

pH Levels

If a seed-starting mix is labeled as having “balanced pH,” the pH should fall between 6.5 and 7. Adjusting the pH level of a seed-starting mix isn’t always essential, since the natural ingredients in most mixes fall within the correct pH levels. Monitoring pH is more important if the plant is grown hydroponically (in water). pH adjusting solutions, known as “pH UP” and “pH DOWN,” are available to mix with the water in a hydroponic system to help maintain a neutral pH level.

Our Top Picks

To qualify as a top pick, a seed-starting mix should be lightweight, contain ingredients that retain moisture, yet drain well, and be free from harmful contaminants. The following products are better suited to some situations than others, but each provides an optimal environment for germinating seeds.

Best Overall

The Best Seed Starting Mix Option: Espoma Seed Starter Potting Mix Natural & Organic
Photo: amazon.com

Espoma’s seed-starting mix contains all-natural ingredients, including sphagnum peat moss, peat humus (a decomposed ingredient from peat bogs), perlite, and Myco-tone, a proprietary blend of ingredients designed to help seedlings develop strong roots. This premium seed-starting mix retains moisture without compacting. Its all-natural formula helps when rooting cuttings, and it produces healthy plants with abundant blooms, making it well suited for both flowers and vegetables. The mix comes in an 8-quart bag.

Pros

  • Great for any seedlings or cuttings
  • Organic mix of sphagnum peat moss, perlite, and mycorrhizae
  • Keeps plenty of oxygen near roots
  • Low nutrient density to prevent burning seedling roots

Cons

  • Smaller bag than expected


Runner Up

The Best Seed Starting Mix Option: Hoffman 30103 Seed Starter Soil, 10 Quarts
Photo: amazon.com

This seed-starting mix from Hoffman, which comes in a 10-quart bag, contains Canadian sphagnum peat moss, vermiculite, limestone (a pH adjuster), and a wetting agent. The mix retains moisture while providing a light, airy growing medium that promotes germination and root development. Also use this seed-starting mix to root cuttings and in larger containers when transplanting seedlings. Ground limestone makes this mix work as a potting soil and for acid-loving plants, such as hydrangea or blueberries.

Pros

  • Great for most seedlings or small transplants
  • Includes limestone as a pH balancer
  • Few sticks and bark in the mix
  • Low nutrient density to prevent burning seedling roots

Cons

  • Finer blend may not work for some plants


Best Bang for the Buck

The Best Seed Starting Mix Option: Miracle-Gro Seed Starting Potting Mix, 8 qt. 2-Pack
Photo: amazon.com

From a manufacturer well-known in the gardening industry, this Miracle-Gro mix is specially formulated to boost root development. Miracle-Gro contains sphagnum peat moss, perlite, fertilizer, and a wetting agent. The mix helps retain moisture and drains well, and it won’t pack down.

The included fertilizer contains nitrogen, phosphate, and potash to help stimulate sprout growth, root development, and blooms. This Miracle-Gro product, which comes in two 8-quart bags, is suitable for starting root and leaf cuttings as well as seeds. Also use it in larger containers when transplanting.

Pros

  • Two-pack of potting mix for seeds or cuttings
  • Enriched with fertilizer for accelerated root growth
  • Wetting agent keeps mix moist

Cons

  • Too many sticks


Best Organic

The Best Seed Starting Mix Option: Coast of Maine Organic Seed Starter Sprout Island
Photo: amazon.com

From Coast of Maine, this organic mix contains a blend of ingredients designed specifically for starting seeds and root cuttings, including sphagnum peat moss, perlite, aged compost, kelp meal, and worm castings. The mix also contains an all-natural fertilizer to encourage growth and help produce disease-resistant plants.

Coast of Maine’s seed starter is a lightweight, well-draining growing medium that won’t pack down, so tender seedling roots can develop. It retains moisture to help prevent roots from drying out. The mix comes in a 16-quart bag.

Pros

  • Includes worm castings, kelp, poultry manure, and more
  • Naturally retains moisture
  • Nice earthy aroma

Cons

  • Some mixes have too many hard chunks or twigs


Best Coconut Coir

The Best Seed Starting Mix Option: Burpee Organic Coconut Coir Seed Starting Mix 16 Qt.
Photo: amazon.com

The coconut coir in this seed-starting mix comes in the form of a compressed brick. Just add water and crumble the product to produce 16 quarts of seed-starting mix, containing a straightforward combination of coconut coir and, to help promote plant and root growth, bone meal.

Use the coir in any seed-starting container, by itself or together with potting soil to grow larger plants. The material retains moisture yet won’t pack down.

Pros

  • Expands to create up to 8 quarts of coir mix
  • Helpful medium to aerate soil
  • Renewable resource for organic or conscious gardening

Cons

  • Takes extra time to prepare the coir
  • Can only prepare when needed; otherwise it sits and molds


Best Pellets

The Best Seed Starting Mix Option: 50-Count Jiffy 7 Peat Pellets Seed Starter Plugs
Photo: amazon.com

Jiffy’s peat pellets are small, compressed discs that expand into fluffy grow pods when immersed in water. The pellets contain only compressed peat moss—nothing else. The user places a pellet in the bottom of a plastic flat or tray and pours in warm water to trigger expansion. When the expansion is complete, the pellet measures 1.5 inches by 1.5 inches—just large enough to insert a seed or two in the top of the peat moss.

The peat moss is held in place with a thin biodegradable net, and gardeners place the entire unit in the soil when transplanting to the garden or a larger pot.

Pros

  • Easy to use, and no soil required
  • Helps reduce transplant shock
  • Pack of 50

Cons

  • Netting doesn’t always break down naturally when transplanted


Best Window Kit

The Best Seed Starting Mix Option: Window Garden Seed Starting Kit – Complete Supplies
Photo: amazon.com

This all-inclusive seed-starting kit features three grow trays that are small enough to fit on a windowsill. Each tray comes with 10 compressed coconut coir grow pods. A clear dome sits atop each tray to act as a mini-greenhouse and help keep the pods from drying out.

Put the coconut coir pods in the bottoms of the trays and add warm water; the pods will expand and become light and fluffy. When the seedlings are ready for transplanting, insert the entire pod in the garden.

Pros

  • Includes three enclosed trays and several seed plugs
  • Plugs can be transplanted directly into soil
  • Tray lids simulate warm greenhouse
  • Fits on most windowsills at 4 inches wide

Cons

  • Mesh net might need to be removed before transplanting
  • Trays may feel flimsy


Best for Hydroponics

The Best Seed Starting Mix Option: Urban Leaf AeroGarden Compatible Sponges (50 Pack)
Photo: amazon.com

To start seeds in a consumer hydroponic system, consider using these convenient sponges. Each holds a single seed for germination and provides growing support for the plant’s entire life. Place one sponge pod in the basket of a home-type hydroponic system, add seed, water, and liquid nutrients as recommended by the manufacturer. The hydroponic system takes care of the rest by circulating water and providing light.

Urban Leaf’s sponge seed pods are compatible with AeroGarden and many other home hydroponic systems.

Pros

  • Made primarily with coconut coir
  • Maintains its shape well
  • Soft interior for better soil aeration

Cons

  • Only suitable for AeroGarden pods
  • Shipped moist and could have mold


Also Consider

The Best Seed Starting Mix Option: Sun Gro 1311002 8-Quart Seedling Mix
Photo: amazon.com

Help seedlings thrive with Sun Gro’s seedling mix, which contains Canadian sphagnum peat moss, perlite, and a trademarked organic wetting agent for moisture. This mix provides a well-draining, lightweight growing environment that promotes root growth and retains moisture to keep the mix from drying out.

Use Sun Gro’s product to start seeds or to propagate cuttings in plastic flats, trays, or other containers. Note that because it’s organic, this mix can safely be used to grow fruits and vegetables for consumption.

Pros

  • Contains Canadian sphagnum peat moss, perlite, and yucca
  • Great for seed germination or transplants
  • Low nutrient density to prevent burning seedling roots

Cons

  • Might need an additional aeration medium like coir or perlite


Our Verdict

Seed germination can be a tricky process to get the right amount of soil, aeration, moisture, and sunlight, but using one of the best seed starting mixes can help you get off on the right foot. We recommend the Espoma Seed Starter Potting Mix as our top choice since it helps with all of the important requirements—aside from sunlight. For a one-and-done seed starter, try the Jiffy Soil Plugs that expand a soil-like mix around the seed and can be transplanted as is when the seedling is ready.

How We Chose the Best Seed Starting Mixes

These recommendations include several types of seed starting mixes that have proven effective at accelerating seedling growth. We reviewed several kinds of traditional sphagnum peat moss mediums that are known to effectively aerate soil and help maintain proper moisture levels for seed germination. Most of these include perlite and other ingredients that help provide optimum soil conditions that are light and moist for seeds to thrive.

We narrowed our research to include other styles of seed starting mixes that are designed for hydroponic pods or can expand when moistened with water. These additional options help provide more recommended choices for every kind of green-thumb gardener. Finally, we also included some organic seed starting mixes to avoid the use of harsh chemicals on delicate seedlings.

Tips for Using Seed-Starting Mix

Use a seed-starting mix rather than soil or potting mix to increase germination and get tiny seedlings off to a healthy start. Employ these tips to simplify the process and increase success.

  • Empty dry mix in a large bowl and stir in water to moisten the mixture before filling a seed flat or seed pots with the mix.
  • If the tap water is high in mineral content, consider using distilled water to avoid creating a high alkaline pH environment.
  • Consider wearing a dust mask when working with a dry seed-starting mix since some contain powdery, fine elements that can become airborne.

FAQs

By using a seed-starting mix, you increase the chance of successfully growing plants to transplant to the garden later. Frequently asked questions about seed starter mixes appear below.

Q. Which type of soil is best for starting seeds?

None, actually! Avoid planting seeds in natural soil; instead, opt for a commercial seed-starting mix for optimal germination and survival rates.

Q. What is the difference between potting soil and seed-starting mix?

Potting soil is denser and may contain larger bits of ingredients, such as twigs or clumps. Seed-starting mix is very fine and contains no large pieces.

Q. Can you reuse seed-starting mix?

No, once it’s been used, it’s no longer sterile. But you can sprinkle leftover mix on the garden or blend it into a potted plant to help lighten the soil.

Q. Does seed-starting mix expire?

No. Seed starting mixes don’t have expiration dates.