Soil conditioners are additives you put in your soil to improve the quality of your soil. Certain plants/vegetation thrives better in their “perfect soil”. There is a wide variety of soil conditioners or amendments, these terms are often interchangeable, however, in some cases a soil conditioner, may refer to a product used for the sole purpose of loosening, or otherwise improving the soil structure in preparation for planting. A soil amendment most often contains a blend of organic or synthetic fertilizers to encourage and help establish plant growth. Even mulch is a soil conditioner since it actively improves the quality of your soil. It is recommended that you add soil conditioners before you plant and often afterwards if using organic soil conditioners.
Soil conditioners are materials added to soil to improve its physical properties like water retention permeability, water infiltration drainage, aeration and structure. The question of how much is needed depends on the project. Here is a guide on determining the right amount of soil conditioner for your gardening or landscaping project.
Why Use Soil Conditioners?
Soil conditioners like compost, manure, peat moss, coconut coir, leaf mold compost, and other organic matter improve soil texture. They increase nutrient and moisture retention. Soil conditioners also help break up compacted soils, improving drainage and aeration. Good soil leads to healthier plants.
Some key benefits of adding soil conditioners:
- Improves moisture retention
- Increases nutrient retention
- Improves drainage and aeration
- Promotes healthier root growth
- Reduces soil compaction
- Increases microbial life and activity
So whether you’re prepping a new garden bed top dressing your lawn or filling a raised bed, soil conditioners are a critical addition for optimal plant growth.
How Much Do I Need?
The amount of soil conditioner needed depends on your specific project. Here are some common gardening and landscaping uses and how much conditioner they require:
Top Dress Lawns
To lightly cover grass seed, apply a 1/8 inch layer of compost.
- 10 sq ft: 1.5 cubic ft bag (extra will be leftover)
- 50 sq ft: 1.5 cubic ft bag
- 100 sq ft: 2 bags in 1.5 cu ft size or 1 bag in 2-3 cu ft size
- 200 sq ft: 2 bags in 1.5 cu ft size or 2 bags in 2 cu ft or 1 bag in 3 cu ft size
- 500 sq ft: 4 bags in 1.5 cu ft size or 3 bags in 2 cu ft or 2 bags in 3 cu ft size
Apply Mulch
To apply a 1 inch layer of mulch:
- 10 sq ft: 1.5 or 2 cubic ft bags, approx. 1 bag
- 50 sq ft: 3 bags in 1.5 or 2 cu ft OR 2 bags in 3 cu ft
- 100 sq ft: 6 bags in 1.5 cu ft OR 5 bags in 2 cu ft OR 3 bags in 3 cu ft
- 200 sq ft: 12 bags in 1.5 cu ft OR 9 bags in 2 cu ft OR 6 bags in 3 cu ft
- 500 sq ft: 28 bags in 1.5 cu ft OR 21 bags in 2 cu ft OR 14 bags in 3 cu ft
Weed Suppression
For a 3 inch layer of compost or conditioner to suppress weeds:
- 10 sq ft: 2 bags in 1.5 or 2 cu ft size
- 50 sq ft: 10 bags in 1.5 cu ft OR 7 bags in 2 cu ft OR 5 bags in 3 cu ft
- 100 sq ft: 18 bags in 1.5 cu ft OR 13 bags in 2 cu ft OR 8 bags in 3 cu ft
- 200 sq ft: 34 bags in 1.5 cu ft OR 25 bags in 2 cu ft OR 17 bags in 3 cu ft
- Over 500 sq ft: Recommend buying bulk
Raised Beds
For new raised beds, fill with a quality potting or raised bed mix.
- 8×4 bed (32 sq ft): 32 bags in 1.5 cu ft OR 24 bags in 2 cu ft OR 16 bags in 3 cu ft
- 4×4 bed (16 sq ft): 16 bags in 1.5 cu ft OR 12 bags in 2 cu ft OR 8 bags in 3 cu ft
Amending Existing Soil
To amend soil with 20% conditioner to 80% existing soil:
- 32 sq ft area: Need 9.6 cu ft of amendment
- Use 7 bags in 1.5 cu ft OR 5 bags in 2 cu ft OR 3 bags in 3 cu ft
Containers
Potting mix quantities needed:
- 5 gallon pot: 0.5 cubic ft
- 1 gallon pot: 3 dry quarts
- 12” pot: 8 dry quarts
- 18” pot: 28 dry quarts
- 14” shallow container: 8 dry quarts
- 18” shallow container: 20 dry quarts
- 3’ window box: 20 dry quarts
- 4’ window box: 1 cubic ft
- 23” high half barrel: 4.5 cubic ft
One 1.5 cubic foot bag fills about twelve 12-inch pots.
Buying Bagged or Bulk Soil Conditioner
When buying soil conditioner, you can purchase bagged product or bulk material. Bulk buying is more cost effective for large projects. Bagged soil is more convenient for small gardens and doesn’t require special delivery or equipment to move onsite.
You can use the soil calculator guidance above to determine how many cubic feet or bags you need based on your project size. Most bagged soil conditioners come in 1, 1.5, 2 or 3 cubic foot bags.
For very large projects like new gardens, amended lawns or commercial sites, consider ordering bulk loads of soil and amendments. Bulk quantities are usually sold by the cubic yard. One cubic yard is equal to 27 cubic feet. You can work with a landscape supply company to deliver and spread bulk materials.
Key Takeaways
- Add soil conditioners like compost to improve soil texture, moisture retention, aeration and nutrition for optimal plant growth
- The amount needed depends on your specific project
- Use 1/8 inch layer for topdressing lawns, 1 inch layer for mulching, and 3 inches to suppress weeds
- For new raised beds, fill entirely with high-quality potting mix
- When amending existing soil, use a ratio of 20% amendment to 80% current soil
- Use portion guidelines to estimate amounts for containers
- Purchase bagged conditioner for small projects, bulk for large gardens or jobsites
With this handy soil conditioner calculator guidance, you can determine the right amount of amendment material needed for your next gardening or landscaping project. Improving your soil will lead to healthier, thriving plants!
Step One: Test the Soil Conditioner
Test your soil to find out what’s missing and what type of soil conditioner you may need. Most universities and colleges have a horticulture department with soil testing facilities. For instance, if your soil has too much clay, sand or is too acidic you will need a soil conditioner.
Measure your yard and/or garden to figure out how much soil conditioner you will need. The recommended application rate is usually specified on the soil conditioner package, and it is important to follow the manufacturer’s guidelines to avoid over-applying and potentially causing harm to the plants. The size of the garden or lawn, the type of plants being grown, and the soil type are also factors to consider when determining the amount of soil conditioner to use. To ensure the best results, it is advisable to seek the guidance of a local horticulturist or soil specialist who can provide personalized recommendations.
Soil Conditioners. What Are They and What Do They Do?
FAQ
Can you use too much soil conditioner?
Measure your yard and/or garden to figure out how much soil conditioner you will need. The recommended application rate is usually specified on the soil conditioner package, and it is important to follow the manufacturer’s guidelines to avoid over-applying and potentially causing harm to the plants.
How much soil conditioner should I use?
Start by spreading a layer of soil conditioner over the top of your soil – generally, a layer of 1-2 inches is sufficient (the amount of soil conditioner you …
How much does a 40 lb bag of soil cover?
A 40 pound bag of topsoil covers 12 square feet (one inch deep).
What is the ratio of soil conditioner to soil?
In-Ground Plantings:
Pack remaining space around plant with 1/2 native soil and 1/2 Soil Conditioner. Water thoroughly.