When the weather warms, gardeners often head outdoors to sow quick-sprout vegetables, such as cucumbers, squash, and tomatoes. Starting seeds indoors is also a rewarding, economical way to get a jump on the gardening season, but it can be tricky.
To reduce the risk of seedling failure, you need to 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 seed germination. Read on for some of the top seed starting mixes available today and some things to keep in mind while you shop.
- BEST OVERALL: Espoma Organic Seed Starter Premium Potting Soil Mix
- RUNNER-UP: Hoffman Seed Starter Potting and Planting Soil
- BEST BANG FOR THE BUCK: Miracle-Gro 8-Quart Seed Starting Potting Mix
- BEST WINDOW KIT: Window Garden Mini Greenhouse Seed Starter Kit
- BEST COMPOST-BASED: Purple Cow Organics Natural Compost Seed Starter Mix
- BEST ORGANIC: Coast of Maine Sprout Island Organic Seed Starter
- BEST COCONUT COIR: Burpee Organic Coconut Coir Seed Starting Mix
- BEST STARTER PELLETS: Jiffy-7 36-Millimeter Peat Pellet Seed Starter Plugs
- BEST FOR HYDROPONICS: Urban Leaf AeroGarden Compatible Grow Sponges
- BEST PEAT-FREE: SpongEase Pro Coco Coir Brick
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.
How We Chose the Best Seed Starting Mixes
We researched the most sought-after seed starting mixes in their respective categories and discovered that the best options are determined by their ingredients, form, quantity provided, and other special features included by top brands.
While searching for the best seeding mix available, the most effective and popular types among users for outdoor and indoor plant growth were potting soil mixes, pods, and sponges. These mixes included coconut coir, sphagnum peat moss, perlite, fertilizer, wetting agents, and even compost.
The seeding mixes allow for drainage, water-retention, root cutting, and transplanting while young seeds begin to grow. Many come with large quantities of up to 16 quarts or 50 pods or sponges. Plus, the majority of these picks are 100 percent certified organic seed starters.
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 seeding mix provides an optimal environment for germinating seeds.
Espoma’s organic seed starter 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. This potting mix comes in an 8-quart or 16-quart bag.
- Ingredients: Sphagnum peat moss, perlite, limestone to adjust pH, and yucca extract
- Quantity: 8 or 16 quarts
- Organic: Yes
- All-natural potting mix for start seeds and root cuttings; helps improve moisture retention
- Noncompacting; intended to promote better root growth; also suitable for vegetables and flowers
- Some users who used this product have reported poor growth with some plants
Get the Espoma seed starting mix at Amazon or TrueValue.
This seed-starting mix from Hoffman, which comes in a 4-, 10-, or 18-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 seed 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.
- Ingredients: Sphagnum peat moss, vermiculite, limestone, and a wetting agent
- Quantity: 4, 10, or 18 quarts
- Organic: No
- Lightweight, loose, and fertile soilless mix; specially formulated to promote seed germination and root development
- Contains 6 components blended in proper proportions; can be used for fruits, vegetables, and flowers
- Also suitable for root cutting and transplanting; absorbs water well
- May take some time to fully germinate some seeds, leading to a slower sprout
Get the Hoffman seed starting mix at Amazon or Kmart.
From a manufacturer well-known in the gardening industry, this Miracle-Gro potting 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 an 8-quart bag, is suitable for starting root and leaf cuttings as well as seeds. Also use it in larger containers when transplanting.
- Ingredients: Sphagnum peat moss, perlite, fertilizer, and a wetting agent
- Quantity: 8 quarts
- Organic: No
- Enriched with Miracle-Gro Plant Food; formulated to boost root development
- Good choice when starting from seed or starting plants with leaf, stem, or root cuttings
- This seed starting mix is intended for container use only
- Some users report a sour smell out of the bag
Get the Miracle-Gro seed starting mix at Amazon (2-pack), Ace Hardware, The Home Depot, Lowe’s (2-pack), or Tractor Supply Co.
This Window Garden 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 fiber soil pods in the bottoms of the trays and add warm water; the pods will expand and become light and fluffy. Each pod contains only organic coconut coir. When the seedlings are ready for transplanting to garden soil, insert the entire pod in the garden.
- Ingredients: 30- to 36-millimeter fiber soil (coconut coir)
- Quantity: 3 trays with 10 cells each (30 cells total)
- Organic: Yes
- 3 mini greenhouses are reusable; create a moist, warm environment needed for reliable seed germination
- Have a better root system, capable of absorbing more oxygen, moisture, and nutrients
- New plants can be transplanted directly into a garden or planter
- Pricey compared to other seed starter kits on the market
- Seeds are not included with this kit and must be purchased separately
Get the Window Garden seed starting mix at Amazon or Bed Bath & Beyond.
Purple Cow Organics’ seed starter mix contains sphagnum peat moss, perlite, vermiculite, and natural compost derived from yard trimmings. It also includes an all-natural blend of trace minerals and nutrients to boost plant health, promote rapid germination, and encourage strong, sturdy seedlings.
The mix is lightweight, offers moisture retention, and provides aeration for tender roots to develop. The activated compost provides added nutrients to feed young plants for up to 45 days. Although the mix bears the name Purple Cow, it contains no manure, and it comes in a 12-quart or a 1-cubic-foot bag. It is intended for seed starting in trays, blocks, or small containers.
- Ingredients: Natural compost, sphagnum peat moss, perlite, vermiculite, rock and sea minerals, fertilizer
- Quantity: 12 quarts or 1 cubic foot
- Organic: Yes
- Provides excellent moisture retention and aeration for increased germination and seedling vigor
- Includes fertilizer and trace minerals to add richness to garden soil
- Works up to 45 days; ample time for seeds planted in trays, blocks, or containers
- Some users report finding several small pebbles and sticks in this mix
- May be too chunky for proper seed germination with inadequate water retention to support growth
Get the Purple Cow Organics seed starting mix at Amazon or Target.
This Coast of Maine organic seed starter 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 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 8- and 16-quart bags. There’s also a 2-cubic-foot option.
- Ingredients: Sphagnum peat moss; composted manure; mycorrhizae; fertilizer from poultry manure, lobster and crab shell, kelp meal, and worm castings
- Quantity: 8 or 16 quarts or 2 cubic feet
- Organic: Yes
- Designed specifically for germinating seeds and rooting cuttings to grow healthy, disease-resistant plants
- All-natural fertilizer made with rich ingredients, including kelp meal, worm castings, and lobster meal
- Lightweight garden soil that provides ample drainage and water retention
- Some users report poor consistency and mold; some say this mix attracts flies
Get the Coast of Maine seed starting mix at Amazon, The Home Depot, or Target (2-pack).
The compressed coconut coir in this seed-starting mix comes as an 8-quart, 7.25- by- 6- by-4-inch compressed brick. Just add water and crumble it to obtain 8 quarts of seed-starting mix. The Burpee Organic Seed Starting Mix contains only coconut coir and bone meal to help promote plant and root growth.
Once expanded with water, use the coir in any seed-starting container, by itself or in combination with potting soil to grow larger plants. The material retains moisture yet won’t pack down.
- Ingredients: Compressed coir soil and coconut husks
- Quantity: 8-quart
- Organic: Yes
- Compact size; when dry, this compressed brick is very easy to store
- Expands to 8 quarts of soil when watered; excellent water retention
- Ideal for seed starting; balanced pH improves nutrient absorption by seedlings or plants
- Tends to dry out faster than other mixes; needs more attention
Get the Burpee seed starting mix at Amazon, The Home Depot, or Burpee (2-pack).
These Jiffy-7 peat pellets arrive in small, compressed discs but 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. Buyers receive 50 compressed peat pellets per package.
- Ingredients: Compressed peat moss
- Quantity: 50 pellets
- Organic: No
- 50 pellets included, with each pod holding 1 to 2 seeds
- Pods are biodegradable, with less use of plastic; suitable for transporting
- Some users reported mold growth after planting seeds with these pods
Get the Jiffy-7 seed starting mix at Amazon or Grower’s Solution.
For starting seeds in an AeroGarden hydroponic system, consider the easy-to-use, soilless seed starting mix from Urban Leaf. Each coco coir sponge 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 AeroGarden hydroponic system takes care of the critical details, such as circulating the water and providing light.
Urban Leaf sponge seed pods are compatible with many other home hydroponic systems, too. The 50 sponges in each bag contain only coconut coir for starting and growing seeds.
- Ingredients: Coconut coir
- Quantity: 50 sponges
- Organic: Yes
- Supports healthy seed germination
- Easy to use and sustainable
- These sponges are mainly compatible with AeroGarden hydroponic gardening systems
- Some users report mold and mildew growth after using these sponges to plant seeds
Get the Urban Leaf sponges at Amazon or AeroGarden.
The SpongEase Pro Coco Coir Brick squeezes nutrients down to a compact brick full of goodness. Made of raw coconut coir, this fibrous block expands to a light texture designed to aerate, retaining moisture. At the same time, it provides a nutritious boost for starting seeds.
Gardeners can rehydrate the entire block to create 2 gallons of soil or hydrate only the amount needed for a specific project. The compressed packaging stores easily and provides options for a wide range of gardening needs and uses. This organic and eco-friendly brick makes a good substitute for peat since coco coir saturates more quickly than peat moss, although it dries out more quickly, so be aware of this when using.
- Ingredients: Coconut coir
- Quantity: 1 brick makes 2 gallons of soil
- Organic: Yes
- Compact and easy to store when not using; more environmentally friendly than peat moss products
- Affordable considering that the product makes 2 gallons of soil
- Texture may be grittier compared to other coco coir product; resulting in slower growth
Get the SpongEase seed starting mix at Amazon or The Home Depot (3-pack).
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 garden 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 garden soil. Seed-starting mix has a light, airy consistency, so tender roots and sprouts can grow without resistance.
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.
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 garden 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.
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.
Tips for Using Seed-Starting Mix
Use a seed-starting mix rather than soil or potting mix to increase seed 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.
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 indoors?
None, actually! Avoid planting seeds in natural soil; instead, opt for a commercial seed-starting mix for optimal germination and survival rates. The best starting soil only needs three ingredients for seeds to germinate: sphagnum peat moss (or coco coir), perlite, and vermiculite.
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. Potting soil usually does not drain as well as starting mix and is packed with richer nutrients (which seeds don’t actually need to germinate)
Seed starting mix is very fine and contains no large pieces, drains well, and helps prevent compacting inside the small seed starting cells or containers.
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. However, users should take care when storing unused starting mix to prevent mold growth or bugs.
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