Comparison Between Potting Soil & Regular Garden Soil?
Potting soil (or potting mix) differs fundamentally from "regular soil" (i.e., natural garden or field soil) in composition, structure, and purpose. It's primarily designed to meet the growing needs of potted plants.
Below is a detailed comparison:
Here’s a clear English comparison between potting soil (potting mix) and regular garden soil:
| Aspect | Potting Soil (Potting Mix) | Regular Garden Soil |
|---|---|---|
| Main Ingredients | Peat moss, coco coir, perlite, vermiculite, bark fines, compost | Natural minerals (clay, silt, sand) + organic matter (humus) |
| Drainage | Excellent – perlite/vermiculite create air pockets; water drains fast | Varies: clay = poor & compact; sandy = too fast |
| Water Retention | Balanced – peat/coir hold moisture and release slowly | Unstable: clay holds too much; sand dries out quickly |
| Aeration | High – loose, fluffy texture allows roots to breathe | Often poor due to compaction |
| Weight | Lightweight (0.2–0.4 g/cm³) – easy to move pots | Heavy (1.2–1.5 g/cm³) – not ideal for containers |
| Nutrients | Starts with slow-release fertilizer (1–3 months); low overall, needs feeding | Depends on soil fertility; may deplete over time |
| pH | Adjusted to 5.5–6.5 (optimal for most plants) | Varies by region (often acidic in Taiwan, pH 4.5–6.5) |
| Sterility | Sterilized – free of pathogens, weed seeds, pests | Contains microbes, insect eggs, weed seeds |
| Direct Use in Pots? | Yes – ready to use | No – causes root rot, compaction, pests |
Regular soil is relatively hard and consists solely of soil. This is suitable for plants that have already germinated.
The potting soil is very loose and fine, and contains some very small dead branches, making it suitable for seedlings. Once the seeds have germinated, they can be moved to regular soil for growth. While potting soil is more nutritious than regular soil, it's so loose that the fully grown plants still need to be placed in regular soil, otherwise the roots won't be able to take hold. You can sprinkle a layer of potting soil on top of the regular soil to replenish the soil's organic matter.
Good soil should have at least 3 qualities:
1. Loose texture, good aeration, and drainage.
2. High water retention.
3. Fertile.
Potting soil
The quality of potting soil is determined by the amount of weed seeds it contains and its water retention capacity. Remember, potting soil is not soil; it must be replaced after one year. It's different from regular soil.
Potting soil is fully fermented, clean, and free of contaminants, pathogens, pests, debris, or weed seeds.
In fact, you can mix the potting soil with some sandy soil for better results. This will also improve drainage and prevent the bottom of the pot from becoming too wet, which could lead to root rot. Alternatively, you can compact the potting soil. Since potting soil is generally very loose, compacting it should not damage the plant's roots. Finally, place some larger stones on top of the potting soil to stabilize it and prevent it from splashing out when watering. Effective soil additives:
Gravel: Made from expanded refining stone, it has excellent water-retention properties and can be used for gravel cultivation or drainage.
Coal: It absorbs excess minerals and waste, maintaining the quality of the potting soil.
Coarse sand: It loosens the potting soil, allowing for easier aeration and drainage.
Powdered limestone: It effectively reduces the acidity of the potting soil.
Eggshells and oyster shells: They reduce the acidity of the potting soil and aid drainage.
Humus: It retains nutrients and provides a loose texture. Limestone: Reduces the acidity of the potting soil and aids drainage.
Peat moss: Retains moisture and adds nutrients.
Perlite: Makes the potting soil loose, facilitating aeration and drainage.
Cotton wool: Keeps the potting soil moist and allows air to penetrate.
Sphagnum moss: Excellent water-retaining material.
Bark: Retains moisture and adds nutrients.
Why can't you use regular soil for potted plants?
Poor drainage → Roots are soaked for extended periods, leading to root rot (especially for succulents and orchids).
Excessive weight → Large potted plants are difficult to move, and excessive weight is required for balconies.
Pest and disease risk → Potentially introduces nematodes, fungi, and weeds, affecting the indoor environment.
Unstable nutrient content → Fertility may be high initially, but quickly depleted or salinized.
The following summarizes the differences in specialized potting soil formulas for common plant types. Each type has been adjusted for drainage, water retention, aeration, pH, and nutrients, ensuring optimal plant growth.
1. Succulents & Cacti
Goal: Extremely fast drainage, root rot resistance, and drought tolerance
Ingredients and Ratios
50–70% coarse sand, volcanic rock, Kanuma soil, Akadama soil (particle size 3–6mm)
20–30% peat moss or coconut coir (a small amount for water retention)
10% perlite, vermiculite, crushed charcoal (to increase aeration)
pH: 5.5–6.5 (slightly acidic)
Features: Almost no water accumulation; water only when soil is completely dry.
Recommended commercial options: Succulent soil, cactus soil, and imported "Succulent Mix."
2. Orchids
Goal: Ultra-high aeration, epiphytic root respiration, slightly damp but not wet
Ingredients: 60–80% shredded bark (pine or fir bark, 1–2 cm in diameter)
10–20% sphagnum moss (moisturizing but not waterlogging)
10% charcoal granules, perlite, coconut shell granules
pH: 5.0–6.0
Features: Do not use regular soil, as this will suffocate the roots.
Commercially available: Phalaenopsis soil, Chinese orchid soil, imported Orchid Bark.
3. Foliage Plants
Goal: Water retention but not wetness, strong root system
Ingredients: 40–50% peat moss (main water retention)
30% perlite + vermiculite (aeration and drainage)
20% coconut fiber or compost (nutrients)
A small amount of slow-release fertilizer, charcoal powder
pH: 5.5–6.5
Features: Moist but not wet, suitable for humid indoor environments. Commercially available: General Foliage Soil, Aroid Mix.
4. Seedling Planting
Goal: Fine, sterile, good drainage, high germination rate
Ingredients
50% Peat Moss (finely crushed)
30% Vermiculite (water-retaining and breathable)
20% Perlite
pH: 5.5–6.0
Features: Fertilizer-free, sterile (avoids seedling burn and mold).
Commercially available: Seedling Soil, Seed Starting Mix.
5. Acidic Plants (Azalea, Gardenia, Blueberry, Camellia)
Goal: pH 4.5–5.5, for easy iron absorption
Ingredients
50% Peat Moss (naturally acidic)
30% Pine Needle Compost or Pine Bark
20% Perlite + a small amount of sulfur powder (to adjust the acidity)
Commercially available: Azalea Soil, Azalea Mix, Rhododendron Soil.
6. Vegetable/Herb Soil (for potted cherry tomatoes, basil)
Goal: High nutrients, good drainage, and a strong root system
Ingredients: 40% high-quality compost or organic matter
30% peat moss or coconut fiber
20% perlite
10% vermiculite + slow-release organic fertilizer
pH: 6.0–7.0
Commercially available: Vegetable potting soil, organic potting soil.
7. Hydroponics to Soil/Aerial Root Plants (Air Plants, Staghorn Ferns)
Goal: Minimal soil use, attached and breathable
Medium: Sphagnum moss, bark, driftwood, coconut coir
Method: Tie or hang, without burying roots.
Quick Comparison Chart (Easy to Understand)
| Plant Type | Drainage requirements | Water conservation needs | pH | Key Materials |
|---|---|---|---|---|
| Succulents/Cacti 多肉/仙人掌 | ★★★★★ | ★☆☆☆☆ | 5.5–6.5 | Sandstone, volcanic rock |
| Orchid 蘭花 | ★★★★★ | ★★☆☆☆ | 5.0–6.0 | Tree bark, moss |
| Foliage Plants 觀葉植物 | ★★★☆☆ | ★★★★☆ | 5.5–6.5 | Peat moss, perlite |
| Seedling 育苗 | ★★★☆☆ | ★★★☆☆ | 5.5–6.0 | Vermiculite, fertilizer-free |
| Azalea/Blueberry 杜鵑/藍莓 | ★★★☆☆ | ★★★★☆ | 4.5–5.5 | Peat moss, pine needles |
| Vegetable 蔬菜 | ★★★★☆ | ★★★☆☆ | 6.0–7.0 | Compost, perlite |
Reminders
Don't mix soil: Succulent soil will be too dry for orchids, and orchid soil for succulents will rot their roots. Expired soil: Nutrients decrease after 6 months of opening and mold growth may occur. It is recommended to replace it with new soil.
Homemade sterilization: If you are mixing garden soil, microwave it for 5 minutes or oven-bake it at 80°C for 30 minutes to sterilize it.
Special circumstances
If you want to make your own potting soil, use 30% garden soil, 40% peat moss, 20% perlite, and 10% organic fertilizer, but sterilize it at high temperatures (microwave or oven-bake it at 80°C for 30 minutes).
For succulents/orchids, increase the proportion of gravel in potting soil (to prioritize drainage); for foliage plants, increase the proportion of peat (to retain water).
Conclusion
Potting soil is an "artificially optimized soil" designed specifically for potting. Regular soil is suitable for field or ground cultivation and will generally fail when used in pots.
Reference: Taiwan Agricultural Knowledge Website
