There are three main types of soil: sand, silt, and clay. The best soil for most plants to ensure optimum growth is a rich, sandy loam. This soil is an even mixture of all three main types of soil. In most cases, you'll need to amend the soil with compost. Depending on how compact the soil is, you may need to add peat moss and sand. However, there are many plants that are well adapted and can grow in particular types of soil.
Different Plants for Different Soils
Soil is generally described by the amount of sand, clay, and silt it contains. This is known as texture. Soil texture is directly related to nutrient quality and drainage capabilities.
A loam soil contains a nice balance of silt, sand, and clay along with humus. The factors that make this soil type so desirable and good for growing plants include:
- Higher pH level: The best pH for most plants is between 6.0 and 7.0. The pH level affects the plant's ability to grow. This range of acidity allows good plant nutrients to thrive as well as other soil organisms, such as earthworms.
- Higher calcium level: Plants need calcium for healthy growth. Calcium helps maintain the balance of soil chemicals. It also ensures that water reaches the roots of plants by improving the soil's ability to retain water. It also contributes to creating the looseness of the soil, so oxygen reaches the roots. Calcium reduces the amount of salt in the soil. Too much salt damages the root systems and limits the plant's growth and ability to absorb nutrients.
- Gritty texture: The soil is dry, soft but gritty to the touch, and crumbles easily to provide excellent draining properties. The soil texture also retains water and plant nutrients. This benefits the plants with consistent moisture and food. Since the soil is crumbly, the air flows easily all the way to the roots.
Sand is the largest particle in soil and does not hold nutrients well. The following plants are well-adapted to sandy soil.
- Blanket Flower: Drought tolerant, this flower thrives in nearly pH neutral soil found in sandy soil.
- Adam's Needle: This yucca plant prefers sandy soil and tolerates salt spray. Its roots rot in damp soils.
- Wormwood: This perennial herb is drought-tolerant and prefers dry sandy soils that aren't very fertile.
- Butterfly weed: Attract butterflies with this sun-loving plant that prefers poor, dry sandy soil.
Soils with a large amount of clay are heavy and do not drain well. The following plants are well-adapted to clay soil.
- Bee Balm: Some species grow in sandy soils, while others prefer loamy or clay soils. Check before buying which soil the plant prefers.
- Black-eyed Susan: This flower can grow in a range of soils from loamy to clay. It needs good soil drainage, so you may need to amend your flower bed.
- Goldenrod: This wildflower is adaptable to most soil types, including clay.
Silty soil is powdery with high fertility. Unfortunately, soils that are high in silt can become waterlogged very easily. The following plants are well-adapted to silty soil.
Best Soil for Flowers
The best soil to use for flowers depends on the type of flower, such as bulb vs seed, and where you're growing it. For example, flower bulbs will thrive in sandy loam soil.
- Sandy loam soil provides excellent drainage to prevent the bulb from rotting and the roots can grow easily.
- The texture of potting soil is best when planting flowers in a container, such as a window box or flower pot.
- For a flower garden, you can use a soil mixture of compost, peat, and topsoil as a general mix with a 1:1:1 ratio.
Best Soil for Vegetables
The best soil for a vegetable garden depends on the type of garden you have. For a raised bed garden you want a 50/50 ratio of compost and topsoil. For a field garden you need soil that drains well. Clay soil will need to be amended to ensure the water drains properly. You can amend using gypsum, vermiculite or expanded shale.
Soil for Indoor Plants
If you're growing houseplants, you might think it's a good idea to scoop some soil from your yard to grow your plants in. This is actually a bad idea since garden soil contains bacteria that can be harmful to your houseplants. There are a two options if you don't want to use commercial potting soil.
Sterilize the Outside Soil
If you opt for your outdoor soil to grow your indoor plants, you'll first need to pasteurize it in order to eliminate any diseases, as well as insects and weeds. Spread it on a cookie sheet and bake in a 180 degree oven for 30 minutes. Although this process will emit a bad odor, it does take care of the bacteria.
After the soil is sterilized, you'll likely need to amend it with peat moss and sand. These are things that will allow proper drainage and air flow while still retaining the right amount of moisture. Commercial potting soils are similar. They include peat moss and vermiculite along with a slow-release fertilizer. Together these things create a soil mix that holds nutrients, retains moisture, and provides ventilation for the roots of the plant.
Create Your Own Mix
Another option is to make your own potting soil. This will allow you to control the quality of the soil. A recipe for a lightweight soilless planting medium includes:
- 1/2 cubic yard peat moss
- 1/2 cubic yard perlite
- 10 pounds bone meal
- 5 pounds blood meal
- 5 pounds limestone
Mix all ingredients thoroughly and store in an airtight container until needed.
Science Fair Project on Best Soil for Plant Growth
You can use different soils in your science project to test which is best for plant growth. Use peat pots or other containers and fill with different soils, such as sand, silt, and clay. Make soil combinations, such as sand and clay, silt and clay and silt, sand, and clay. You may decide to create additional soils using different ratios of various combinations.
Label each pot clearly so you know which soil is in each vessel. Make a not in your journal. If you choose to use a numeric or alphabet coding, make sure you transfer the information accurate in your journal.
Choose Type of Seed
You want to use the same seeds for each soil type. Select the seed according to the type of plant you wish to grow. Flower plants are a popular choice as are herbs.
- Make sure you plant each seed at the same depth.
- Plant two seeds per container in case one seed is defective and doesn't germinate. You can remove the less healthy plant once the second set of leaves appear.
- Plant, water and expose to sun according to the seed packet.
Document Your Experiment
Keep a daily journal on each plant. Make notations on the slightest changes or reactions to the plant growth. You want to observe all differences in the plants as they grow.
How to Measure Your Progress
Your science project needs data to back up your research. There are specific things you can measure to access which soil is best.
- You want to measure the height and width of your plants, daily.
- Document when each leaf unfolds.
- Measure how each plant grows and compare to the others.
- How many flowers does each plant produce?
- Are the number of seeds the same?
- Make sure to take photos or videos of the progress.
Results of Your Experiment
Depending on the requirements for your science project, you need to compile and analysis your journal data and draw a conclusion about which soil type performed the best, based on growth, health, number of leaves, flowers and seeds.
Basil Plant Expermiment Example
This video documents different soils for growing basil plants.
Water Retention, Soil, and Plant Growth Experiment Example
This video shows a project that examined the water retention properties of different soil and how it affects plant growth.
Whether a container garden inside or a garden outside, the key to successful planting is the soil requirements of particular plants. Most soils are a combination of sand, clay, and silt. If you don't know the type of soil, you can use an inexpensive soil testing kit to find out.