How Is Seed Pelleted? Inside the Process Behind Precision Greenhouse Seed

Pelleted seed is commonly used in greenhouse and field operations, but few growers have seen the process that turns a tiny, irregular raw seed into a smooth, uniform pellet. Understanding how pelleting works helps you use pelleted seed more effectively — and appreciate why quality matters at every step.

Each breeding company usually has their own proprietary coating and pelleting formulations. There are also independant  "custom coating" companies that specialize in  coating seeds for both seed companies and individual growers (depending on volumes neeeded)

Step 1: Seed Selection and Grading

Pelleting starts long before any coating is applied. Only high-quality seed lots are selected for pelleting. Raw seed is graded by size, weight, and germination rate before the process begins.

This is a critical point: pelleting can improve seed quality BUT it does not fix poor seed. A low-germination lot will still be a low-germination lot after pelleting. Reputable seed companies pellet only seed that meets strict germination and purity thresholds.

Grading also ensures that seeds entering the pelleting drum are as uniform as possible in size and weight, which helps produce consistent pellet sizes at the end of the process.

Step 2: Pre-Treatment (If Applicable)

Before coating begins, seed may receive pre-treatments depending on the end product specification:

• Fungicide treatments — active ingredients such as thiram, fludioxonil, or metalaxyl are applied to protect against damping-off pathogens (Pythium, Rhizoctonia, Fusarium)
• Biological treatments — beneficial microorganisms or biostimulants may be incorporated at this stage
• Priming — some seed lots are hydroprimed or osmoprimed before pelleting to improve germination speed and uniformity; primed seed is then re-dried before coating

These treatments become part of the pellet, delivering their benefits directly at the seed level during germination.

Step 3: Coating in the Pelleting Drum

The  pelleting process takes place in a rotating coating drum or pan. Seeds are tumbled continuously while coating material is applied in controlled increments.

There are various types of coating drums and coating pans, each with their own characteristics and areas of use

The coating material — typically a blend of inert fillers such as clay, diatomaceous earth, talc, or calcium carbonate — is added in small amounts along with a liquid binder. The binder causes the filler to adhere to the seed surface, building up the pellet layer by layer.

This layering process is repeated many times over the course of the pelleting run. Operators monitor pellet size and roundness throughout, adjusting filler and binder ratios to achieve the target pellet diameter. The goal is a smooth, round pellet that completely encases the seed with no voids or cracks.

The coating material is specifically formulated to:

• Dissolve rapidly or "Split" upon introduction of moisture in the germination medium
• Not restrict radicle emergence once dissolved/split
• Remain intact during handling, seeding, and transport

What Is a Seed Pellet Actually Made Of?

The materials used in seed pellets are carefully selected for their physical properties, safety, and compatibility with germination. A finished pellet "recipe" is composed of several components:

Filler Materials

Fillers make up the bulk of the pellet mass and give it its size, shape, and weight. Common filler materials include:

• Kaolin clay — the most widely used filler; fine-grained, inert, and dissolves readily in moist growing media. Provides good pellet hardness and smooth surface finish.
• Diatomaceous earth (DE) — a silica-based material derived from fossilized algae; lightweight and highly absorbent, often blended with clay to adjust pellet density and dissolution rate
• Talc — a soft mineral used to improve pellet flow and surface smoothness; often used in smaller proportions as a processing aid
• Calcium carbonate (limestone) — used in some formulations to adjust pellet pH and improve dissolution; also contributes to pellet hardness
• Perlite or vermiculite — occasionally used in specialty pellets where lightweight or high-porosity coatings are required

Binders

Binders hold the filler material together and adhere it to the seed surface during the layering process. They must be strong enough to keep the pellet intact during handling and seeding, but dissolve completely and rapidly once the pellet contacts moisture. Common binders include:

• Methylcellulose and carboxymethylcellulose (CMC) — water-soluble cellulose derivatives widely used as food-grade binders; dissolve cleanly in water with no residue
• Polyvinyl alcohol (PVA) — a synthetic water-soluble polymer that provides strong adhesion and clean dissolution
• Natural gums — guar gum, arabic gum, and similar plant-derived binders used in organic-compatible pelleting formulations
• Starch-based binders — modified starches used in some formulations, particularly where biodegradability is a priority

Colorants

Most commercial pelleted seed is colored to distinguish it from raw seed and to identify treatment status. Colorants are inert dyes or pigments applied as part of the coating. Color coding is not standardized across the industry — different suppliers use different color conventions — but within a seed lot, color is a reliable indicator of treatment type.

Active Ingredients (Treatments)

Where seed treatments are included, active ingredients are incorporated into the pellet matrix or applied as a layer within the coating stack:

• Fungicides — thiram, fludioxonil, metalaxyl-M (mefenoxam), iprodione
• Insecticides — imidacloprid, thiamethoxam (note: use restrictions apply; always check label and local regulations)
• Biologicals — Trichoderma spp., Bacillus subtilis, mycorrhizal inoculants
• Micronutrients — zinc, manganese, molybdenum in chelated form for targeted early-season nutrition

Flow Agents and Surface Treatments

A final surface treatment is often applied to finished pellets to improve flow through seeder plates and reduce dust. Common surface agents include talc, graphite, and silica. These are applied in very small quantities and do not affect germination.

Step 4: Sizing and Screening

Once the pelleting run is complete, the batch is screened through a series of sieves to separate pellets by size. This produces a finished lot within a tight size range — for example, 3.0–3.5mm diameter for a standard lettuce pellet.

Consistent pellet size is essential for compatibility with precision seeding equipment. Seeder plates are designed for specific pellet size ranges, and out-of-spec pellets — too large or too small — can cause misfeeds, doubles, or skips.

Undersized and oversized pellets are removed and either re-processed or discarded. Only pellets within the target size range are advanced to the next step.

Step 5: Drying

After coating and sizing, pellets contain elevated moisture from the binder application. They must be carefully dried to reduce moisture content to a safe storage level — typically below 6–8% moisture depending on the crop.

Drying is done at controlled temperatures to avoid heat damage to the seed inside. Too much heat during drying can reduce germination rates or damage seed vigor even if the seed appears intact. This step requires careful monitoring and is one of the areas where pelleting quality can vary significantly between suppliers.

Step 6: Quality Testing

Before release, finished pelleted seed lots undergo a battery of quality tests:

• Germination test — pelleted seed is germinated under standard conditions to confirm germination rate meets label specifications
• Pellet integrity test — pellets are checked for hardness, roundness, and dissolution rate in water
• Singulation test — a sample is run through a precision seeder to confirm singulation performance meets target rates
• Moisture content — confirmed within safe storage range
• Treatment verification — where applicable, active ingredient levels are confirmed.

Lots that fail any quality threshold are rejected or re-processed. This testing step is what separates professional pelleted seed from lower-quality alternatives.

Step 7: Packaging and Storage

Approved lots are packaged in sealed, moisture-barrier containers — typically foil pouches or sealed cans — to protect pellet integrity and seed viability during storage and transport. Packaging includes lot number, germination rate, pellet size, treatment information, and use-by date.

Pelleted seed should be stored in a cool, dry environment. Unlike raw seed, the pellet coating is hygroscopic and will absorb ambient moisture if packaging is compromised, which can cause premature dissolution and reduced shelf life.

What This Means for Your Operation

Understanding the pelleting process helps explain why:

• Moisture management during germination is non-negotiable — the pellet must dissolve fully for the seed to emerge; dry-out at germination is the most common cause of poor stands with pelleted seed
• Pellet size matters for your seeder — always confirm pellet size compatibility with your seeder plate before ordering large quantities
• Not all pelleted seed is equal — the quality of the raw seed, the coating formulation, the drying process, and the testing protocol all affect final performance
• Storage conditions matter more than with raw seed — keep pelleted seed sealed, cool, and dry until use

Browse our Greenhouse Seed catalog for pelleted varieties across Tomato, Cucumber, Lettuce, and Pepper.

Pelleted vs. Non-Pelleted Seed — Paramount Seeds Examples

	Pelleted	Non-Pelleted
Example 1	Tacitus F1 Romaine Lettuce, Pelleted	Maxifort F1 Tomato Rootstock, Non-pelleted, Green Romaine
Example 2	Red Deuce F1 Beefsteak Tomato, Pelleted	Inspired F1 Beefsteak Tomato
Best for	Precision seeding, uniform placement	Hand sowing, or where pellet dissolution is a concern
Seeding	Can be used with precision seeder. Easier to handle.	Compatible with a wider range of methods
Moisture sensitivity	Higher — pellet must dissolve fully	Lower — no coating to dissolve

Final Thoughts

Seed pelleting is a precision manufacturing process — not just a coating applied for convenience. Every step, from seed grading through quality testing, affects the performance you see in the germination chamber. Choosing pelleted seed from a reputable supplier means choosing a product that has been engineered and tested to perform in professional greenhouse conditions.

Questions about pelleted seed?

 Contact the Paramount Seeds team — we're here to help.