--- title: Potting Mix vs Garden Soil vs Seed Raising Mix: What Goes Where canonical: https://gardensuperstore.com.au/insights/potting-mix-vs-garden-soil-vs-seed-raising-mix/ datePublished: 2026-09-15 06:23:55 dateModified: 2026-09-16 01:38:11 author: Jason summary: "Potting mix goes in pots, garden soil goes in beds, seed raising mix goes in trays. Here is what actually separates them, why garden soil drowns a pot, and why the ticks on the bag are only a floor." type: blog_post --- # Potting Mix vs Garden Soil vs Seed Raising Mix: What Goes Where > Potting mix goes in pots, garden soil goes in beds, seed raising mix goes in trays. Here is what actually separates them, why garden soil drowns a pot, and why the ticks on the bag are only a floor. **Short answer:** potting mix goes in pots and containers, garden soil goes in garden beds, and seed raising mix goes in punnets, trays and cells. They are not interchangeable. The difference is physical, not marketing: particle size, air-filled porosity, water holding and nutrient charge are all built to suit a specific container depth and a specific plant stage. Get the match right and your seeds germinate evenly, your potted plants breathe, and your beds hold moisture without going sour. Get it wrong and you spend spring wondering why nothing took off. ## Key takeaways - **Potting mix** is soilless, built for the shallow root zone of a pot. Texture and salt level matter more than the word "premium" on the front. - **Garden soil** is heavier, mineral-based and built to blend into existing ground, not to sit in a container. - **Seed raising mix** is fine, soft and low in nutrients, built for seed-to-medium contact and gentle first roots. - **Read the analysis on the bag.** pH, salt level and nutrient content tell you more than any word on the front. ## The three growing media at a glance Potting mix Garden soil Seed raising mix Where it goes Pots, planters, hanging baskets, grow bags Garden beds, raised beds, backfilling, topdressing Punnets, cell trays, seedling boxes, propagation Base material Soilless: peat or coir, composted bark, sand, mineral components Mineral soil, loam and washed sand blended with composted organics High percentage of fine peat or coir, fine sand, perlite Particle size Varies. Fine peat-based through to coarse bark-based Medium to fine, with mineral grit Very fine and uniform Drainage Fast, holds air at the base of a shallow pot Moderate, relies on the ground below to drain Moderate, holds even moisture in a tiny cell Nutrient charge Varies widely. Some carry 6 to 18 months of controlled release fertiliser, others are starter-charged and you feed from week four Moderate, plus a reserve of humus and organic matter Very low. Just enough to reach transplanting Typical failure if misused Seeds sit in air gaps, fine roots meet too much fertiliser Waterlogged, compacted, airless pots Seedlings run out of food, structure collapses in a big pot ## The real difference is physical, not a label Every growing medium is a balancing act between two things that compete: **water** and **air**. Roots need both. The ratio you get is decided almost entirely by particle size and container depth. Coarse particles create large pores. Large pores drain freely and refill with air. Fine particles create small pores that hold water against gravity. A mix full of fine particles in a shallow container will hold water at the base long after you have stopped watering. That saturated band at the bottom of a container has a name: the **perched water table**. It forms in every pot, and its depth is set by the mix, not by the pot. Use the same mix in a 100 mm pot and a 400 mm pot and the shallow pot will be proportionally far wetter, because the saturated band takes up a much bigger share of the root zone. The perched water table sits at the base of every pot. A shallow pot is proportionally wetter than a deep one. The measure that matters here is **air-filled porosity**, the percentage of air a mix still holds after it has been watered and allowed to drain. It is the number behind why a bagged product designed for the open ground behaves so differently once you shovel it into a pot. The second physical factor is **nitrogen drawdown**. When a medium contains organic matter that has not been fully composted, the microbes breaking it down take nitrogen out of circulation, and your plants compete with them for it. Well-made media are tested for nitrogen drawdown for exactly this reason. It is one of the quiet reasons a cheap, unbadged bag underperforms. ## Potting mix: pots, planters and anything with a base Potting mix is a soilless medium. There is usually no actual soil in it at all. It is built from peat or coir, composted bark and organics, sand and mineral components such as perlite, and it is engineered to stay open and aerated in a confined space. The mix we put ahead of everything else is [Mikskaar Universal Premium Potting Mix](/universal-premium-potting-mix/), a 50 litre bag at $31.90, or $28.71 each if you take five or more. It is neutralised natural peat with a wetting agent and a starter fertiliser charge including trace elements, and it is fine-structured rather than chunky. The reason it earns top spot is what is printed on the bag: pH 5.2 to 6.0, EC 0.7 mS/cm, nitrogen 135 to 225 mg/l, phosphorus 61 to 100 mg/l, potassium 187 to 311 mg/l, density 300 to 320 kg per cubic metre. You are not guessing. [Mikskaar Universal Premium Potting Mix](/universal-premium-potting-mix/), 50 L, $31.90. The trade-off is honest. That starter charge runs about three to four weeks, then you feed. If you would rather the bag did the feeding for you, [Searles Premium Potting Mix](/premium-potting-mix/) carries an eight month controlled release fertiliser and [Searles Platinum Potting Mix](/platinum-potting-mix/) runs to eighteen months, both with re-wetting granules and water crystals. One limit worth knowing on the Mikskaar: it is not suitable for acid-loving plants. Azaleas, camellias, blueberries and gardenias want a specialty mix instead. **Use potting mix for:** indoor plants, patio pots, hanging baskets, potted colour, potted vegetables and herbs, repotting, grow bags. **Do not use potting mix for:** filling a garden bed, where it is expensive and will break down and slump. ## Garden soil: beds, backfill and building ground Bagged garden soil is a blend designed to integrate with the ground you already have. It carries more mineral content, more bulk density and more long-life organic matter than a potting mix. [Searles Premium Garden Soil Mix](/premium-garden-soil-mix/) is a good example of the type, at $18.70 for 30 litres. It blends composted organics, organic manures, mulch and leaf mould with washed river sand and loam, and it is made for establishing new beds, enriching existing ones, opening up heavy clay and building up thin sandy ground. **Use garden soil for:** new garden beds, raised beds, filling and lifting existing beds, backfilling around new plantings, improving clay or sand. If you are not sure what you are working with in the ground, start with our [beginner's guide to understanding garden soil](/insights/starting-strong-a-beginners-guide-to-understanding-garden-soil/), which covers clay, sandy and loamy soils and how to test yours by hand. ### Why garden soil fails in pots Three reasons, in order of how fast they will hurt you: - **It drains too slowly in a shallow container.** The fine particles hold that perched water table high in the pot, the root zone stays saturated, air-filled porosity drops, and roots suffocate. - **It compacts.** Without the open structure of a purpose-built mix, repeated watering settles the particles, the pore space collapses, and water starts running down the inside of the pot instead of soaking through. - **It brings passengers.** Soil-based mixes carry weed seed and whatever else is living in the ground. In an open bed that is background noise. In a 200 mm pot it is competition. If you have already potted something up in garden soil and it is sulking, tip it out, shake the roots free and repot into a mix built for containers. Spring is a forgiving time to do it. ## Seed raising mix: punnets, cells and propagation Seed raising mix is the most specialised of the three, and the one most often skipped. It is light, soft and very finely textured, with a high percentage of peat or coir, and it is deliberately **low in nutrients**. That last point surprises people. A seed carries its own food supply. What it needs from the medium is close contact, steady moisture, oxygen and nothing that will burn emerging root hairs. [Searles Seed Raising Specialty Mix](/seed-raising-specialty-mix/), $23.05 for 30 litres, is milled fine for seedlings and carries only enough fertiliser to get seedlings to transplanting, at roughly the two-leaf stage. After that, you transplant or you start feeding. Even germination across a tray is a texture result before it is a seed result. For cuttings rather than seed, an even more open medium is the right call. [Searles Propagating Mix](/propagating-mix/), $11.40 for 10 litres, uses washed coarse sand, peat moss and perlite for a high strike rate and fast root development. If you would rather mix your own, coir pith is the other route. Our guide to [using coco coir in pots, raised beds and seed raising](/insights/how-to-use-coco-coir-in-your-australian-garden/) covers preparation and ratios, and the [GrowRite coir range](/growing-media-soil-conditioners/coir/) is where to start. ### Why most potting mix fails in seed trays It is not the words on the bag that kill seedlings. It is two specific properties, and plenty of general-purpose mixes have both: - **Particles too big for the container.** A 30 mm cell filled with coarse bark holds only a handful of particles. The air gaps between them are enormous relative to a seed, so the seed never makes proper contact and dries out in a pocket of air. - **A fertiliser load built for an established plant.** A mix carrying six to eighteen months of controlled release fertiliser is designed for a developed root system, not a germinating seed with a root a few millimetres long. - **Moisture that swings too hard.** Coarse mix in a tiny cell dries from the top down very quickly, and germination stalls the moment the seed dries out after imbibing water. - **Uneven germination that looks like bad seed.** Nine times out of ten it is the medium, not the packet. Flip those two properties and the same category of product works. A fine-structured, low-salt substrate like the [Mikskaar Universal Premium Potting Mix](/universal-premium-potting-mix/) is sold for potting, germination and repotting precisely because the texture is fine enough for seed contact and the EC is low enough at 0.7 mS/cm not to punish new roots. That is the distinction worth carrying into the shop: fine and lightly charged is fine for seed, coarse and heavily charged is not. **If all you have is a coarse mix:** sieve it, blend it roughly half and half with [horticultural perlite](/horticultural-perlite/) or [vermiculite](/horticultural-vermiculite/) to fine the structure down and even out moisture, and accept a lower strike rate. ## What actually tells you a bag is good The words on the front do not rank a mix. "Premium" is not a measurement, and neither is "natural" or "organic". What tells you something is the analysis on the back. pH, salt level, nutrient content and density are the numbers that decide whether a mix suits what you are growing, and a bag that publishes them is one you can match to the job instead of guessing at. The [Mikskaar Universal Premium Potting Mix](/universal-premium-potting-mix/) prints all of it: pH 5.2 to 6.0, EC 0.7 mS/cm, nitrogen, phosphorus, potassium, trace elements, density and organic matter content. If you know your plants want a slightly acidic root zone and low salts, you can confirm it before you buy. ## Match the mix to the job - **General potting, repotting and seed raising in one bag:** [Mikskaar Universal Premium Potting Mix](/universal-premium-potting-mix/) - **Seeds in trays or punnets:** [seed raising mix](/seed-raising-specialty-mix/) - **Cuttings:** [propagating mix](/propagating-mix/) - **Pots you would rather not feed for months:** [premium potting mix](/premium-potting-mix/) or [platinum potting mix](/platinum-potting-mix/) - **Herbs and vegetables in pots, bags or beds:** [herb and vegetable specialty mix](/herb-vegetable-specialty-mix/) - **Australian natives and phosphorus-sensitive plants:** [native plant specialty mix](/searles-native-plant-specialty-mix-native-potting-garden-mix/) - **New beds, clay breaking, sandy ground:** [premium garden soil mix](/premium-garden-soil-mix/) - **Mixing your own:** [GrowRite coir](/growing-media-soil-conditioners/coir/), [perlite](/horticultural-perlite/), [vermiculite](/horticultural-vermiculite/) ## Three bags that cover most of spring Product Size Price Best for [Mikskaar Universal Premium Potting Mix](/universal-premium-potting-mix/) 50 L $31.90 Seed raising, potting up and repotting, all from one bag [Searles Premium Potting Mix](/premium-potting-mix/) 30 L From $16.80 Set-and-forget containers with eight months of feed built in [Searles Premium Garden Soil Mix](/premium-garden-soil-mix/) 30 L $18.70 Building and enriching beds before planting out Start seed in the first, pot up into the first or the second, plant out into ground built with the third. That sequence is the whole spring. [Shop growing media](/growing-media-soil-conditioners/) ## Frequently asked questions ### Can I use potting mix in a garden bed? You can, but it is poor value and it will not last. Potting mix is built to be open and lightweight, so it breaks down and slumps once it is in the ground. Use a bagged garden soil or a soil conditioner to build a bed, and save the potting mix for containers. ### Can I use garden soil in pots? Not on its own. In a shallow container, garden soil holds a saturated layer at the base, compacts with watering and starves roots of oxygen. If you only have garden soil, it needs substantial coarse material blended through it, and even then a purpose-made potting mix will outperform it. ### Can you use potting mix for seeds? It depends entirely on the mix. A coarse, bark-based mix carrying months of controlled release fertiliser is the wrong tool: the particles are too big for a seed to make contact with, and the salt level is too high for new root hairs. A fine-structured, low-EC substrate such as Mikskaar Universal Premium Potting Mix is sold for germination as well as potting, and works. Check the texture and the EC, not the word premium. ### What is the difference between seed raising mix and potting mix? Particle size and nutrient load. Seed raising mix is very fine, so tiny seeds make full contact with damp medium, and it carries only enough fertiliser to reach transplanting. Most general potting mixes are coarser and carry months of controlled release fertiliser, which is too strong for germinating seed. ### How long does the fertiliser in potting mix last? It varies by product and the bag will tell you. Starter-charged mixes such as Mikskaar run about three to four weeks before you need to feed. Controlled release mixes commonly run six to eighteen months. Neither is better in the abstract: one gives you control over what your plants get, the other does the work for you. ### Can I reuse last year's potting mix? Old mix has lost structure and nutrition. If the plant was healthy, you can revive it by blending in fresh mix and adding perlite to restore air space, then feeding. For seed raising and for anything valuable, start with fresh media. *Written for Australian conditions by Jason, The Garden Superstore.* [Shop growing media](/growing-media-soil-conditioners/)