Therm-O-Rock Super Coarse Horticultural Vermiculite
Best soil amendment for organic gardeners seeking superior root development.
Elevate your gardening with Therm-O-Rock Super Coarse Horticultural Vermiculite. This OMRI Listed, naturally occurring mineral is heated to expand into lightweight, absorbent particles, perfect for optimizing soil structure. Its super coarse grade ensures superior aeration and moisture retention, promoting robust root development. Packaged in a 4 cubic foot bag, it's an essential component for creating ideal growing mediums for potting, seed starting, and overall plant health, leading to healthier roots and better plant performance.
$49.95
Owner Satisfaction
4.6
/ 5
Category Rank
516
/ 1247
#516 in Soil
Price vs Category Average
-1%
Below average
Volume
4
/ cubic feet
Who it's for
- Gardeners struggling with heavy, compacted soil
- Busy plant owners needing less frequent watering
- Propagators seeking a sterile, reliable starting medium
Who should skip it
- Long-term growers requiring permanent soil structure
- Budget-conscious gardeners managing large-scale projects
- Seed starters working with tiny, delicate varieties
Performance breakdown
Aeration Efficiency
Super coarse grade creates ideal air pockets for vigorous root respiration.
Moisture Retention
Superior absorbent capacity keeps hydration consistent during peak growing cycles.
Organic Integrity
OMRI listing ensures complete compliance for strictly organic gardening standards.
Handling Ease
Lightweight mineral composition makes mixing large batches physically effortless.
Soil Structure Impact
Significantly improves soil porosity for better nutrient uptake and drainage.
Purity Standards
Weed-free mineral base eliminates risk of introducing unwanted garden contaminants.
Key Specs
Volume
4 cubic feet
Grade
Super Coarse
Certification
OMRI Listed
pH Level
7.0
Intended Use
Potting, Seed Starting
Soil Type
Potting Mix
Nitrogen
0.0%
Phosphorus
0.0%
Features
- Enhances soil aeration and drainage
- Improves moisture and nutrient retention
- Promotes healthy root growth
- Lightweight and easy to incorporate
- OMRI Listed for organic gardening
- Naturally occurring mineral
- Super coarse grade for optimal performance
- Versatile for various soil applications
What customers say
Customers consistently praise the superior quality and specific coarseness of this Therm O Rock vermiculite. Gardeners find it exceptionally effective for improving soil aeration and moisture retention, noting that the large particle size minimizes dust and compaction, making it easy to mix into potting mediums. This product delivers reliable performance, significantly enhancing seed starting success and overall plant health, justifying its position as a premium horticultural amendment.
Know before you buy
The super coarse grade provides larger particles that create more air pockets within the soil. This is ideal for long-term potting mixes where you want to prevent compaction and ensure roots have plenty of oxygen.
Yes, this product is OMRI Listed, meaning it meets the standards for use in certified organic gardening. It is a naturally occurring mineral that is free of synthetic additives.
No, this is a pure mineral amendment with 0-0-0 NPK levels. It is designed to improve the physical structure of your soil rather than provide direct nutrition to your plants.
While it is excellent for general potting, the super coarse grade is best suited for larger containers or mixing into garden beds. For very fine seeds, you might prefer a finer grade, though this can still be used if incorporated into a custom seed-starting blend.
With a neutral pH of 7.0, this vermiculite is chemically inert and will not significantly alter the acidity or alkalinity of your growing medium.
A 4 cubic foot bag is quite substantial and is intended for larger projects. It is sufficient to amend several large containers or a significant portion of a raised garden bed when mixed with compost and peat or coco coir.
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$50