Its all about the soil....
No matter what type of gardening techniques you use, you will have trouble raising healthy plants if you do not have strong soils. Soil is much more than just "dirt", and healthy soil is the basis for a healthy garden. Because different plants thrive in different types of soils, knowing what type of soil you have before you begin to plant your garden will help you plan for success. When you know what type of plants will match your soil, you can also amend and improve your soil; a careful gardener will be able to improve soil with every passing season.
The two primary soil characteristics that a gardener should know are soil texture, which will determine how moisture and nutrients are held in the soil, and pH level, which will determine which types of trace minerals are available in the soil. This page will tell you about these different types of soils, how to determine what soils are present in your garden, and how to make the most out of the soils you have through different soil improvement techniques. To learn more about the techniques described here, as well as other gardening basics, check out the American Community Garden Association's publications at the ACGA STORE
Soil texture is difficult to change on a large scale, so knowing the type of texture your soil has will help you decide what type of plants to plant. The "ideal" type of soil for many plants is loam, which is a mix of sand, silt, and clay, but most soils will lean toward either a clay texture or a sandy texture. It is easy to test your soil texture so that you know what type of plants will do best in your garden.
Types of Soil Textures
- Water retentive even in drought; moist and fertile
- When managed well, can be suitable for a wide range of plants
- Slow to warm in spring, which leads to a shorter growing season
- Sticky/difficult to work when wet
Improving Clay Soil
- Adding compost or yard debris will help reduce compaction
- Adding fine gravel or coarse sand will help improve drainage
Plants for Clay Soils
- Suitable for growing moisture-loving plants
- Because of its water-retaining characteristics, clay soil makes a good site for a natural pond or bog
- Quick draining and easy to work
- Quick to warm in spring, which leads to a longer growing season
- Dries quickly in times of drought
- Organic matter breaks down quickly
- Nutrients are quickly washed out, requiring fertilizer application
Improving Sandy Soil
- Mulch with organic matter to improve moisture retention
- Plant a cover crop, such as clover or buckwheat, to add organic matter to the soil
- Soils are prone to high acidity which requires the application of lime; regularly testing pH level is recommended
Plants for Sandy Soils
- Annuals and drought-tolerant plants
- Many types of trees can handle drought well, once established
- Holds moisture and nutrients, so plants will need minimal watering or fertilization
- Supports the widest range of plant types
- Because of high nutrient levels, over fertilizing is possible
- You will still need to test and maintain the soil pH level
- Not ideal soil for a wildflower meadow, which requires low nutrient levels
Plants for Loamy Soil
- Most types of plants will grow well in these soils
- Demanding plants, which require a balance of moisture and nutrients, will thrive in loamy soil
Testing your Soil Texture
Testing soil texture is a simple process. Take a small handful of moist soil into your hand, and shape it into a ball. Then try to work it into a tube shape, and rub it between your fingers. Different soils will act in different ways:
- Feels smooth and sticky when formed into a ball
- Will hold up well when rolled into a tube; will bend into a ring
- Shiny when rubbed between fingers
- Feels gritty and will not form a ball or tube
- Crumbles when rubbed between fingers
- Will form a ball, and will show finger impressions
- Smooth when rubbed between fingers, without being sticky
While "pH Level" can sound like a daunting, overly scientific term, it can help you understand what type of plants will thrive in your soil. The pH scale runs from 1.0 to 14.0, and measures how acidic or alkaline ("limey") the soils are - the lower the soil pH level the more acid is present in the soil. Soil acidity will determine how easily your plants can access certain important trace elements such as manganese, aluminum, and iron.
It is important to test your pH level to know what plants will grow well in your soil, and what type of techniques you should use to make your soil friendlier to more types of plants. While most plants prefer soils that are "neutral" (not too acid or too alkaline), a few plants prefer a specific pH level and may require frequent testing and feeding if the soil is not naturally suited to their needs. For detailed information on pH levels and plant compatibility, check out our Online Resource Library.
Alkaline soils, or "sweet" soils, have high pH Levels (over pH 7). Contain high levels of calcium; low levels of iron, phosphorus, manganese and iron.
- Generally well-drained
- Quick to warm in spring
- Plants generally grow to be sturdy in these soils
- Will not support acid-loving plants
- Raising soil acidity is costly and impractical
Coping with Alkaline Soils
- Incorporate large amounts of organic matter to make nutrients more accessible and raise moisture retention
- To lower soil pH, add a source of acid, such as pine needles, shredded leaves, sulfur, sawdust, or peat moss
Plants for Alkaline Soils
- Lilacs, clematis, geraniums, eucalyptus, cabbage, cauliflower, celery, cucumber, thyme
Acidic soils, or "sour" soils, have low pH Levels (under pH 7.0). Contain low levels of calcium, nitrogen, phosphorus, and potassium; high levels of manganese and aluminum.
- Moderate levels of acidity will support most plants
- Very acidic soils (pH of 4.5 or lower) can be toxic for some plants
Coping with Acidic Soils
- To raise the pH of the soil, add an alkaline material, such as ground limestone ("lime") or wood ash
Plants for Acidic Soils
- Azalea, rhododendron, lupine, lily, hydrangea, blueberry, eggplant, raspberry, rhubarb, shallot, sweet potato, watermelon
Test your pH Level
Testing your pH level is something that should be done when starting a garden and about every two to three years thereafter. To undertake a soil test, you can either send soil samples in to a laboratory or do a soil test yourself with a take-home kit. If you want a more detailed, accurate set of results, sending it in to a laboratory is the best option; usually local university extension offices will maintain a listing of regional labs that do soil testing, and extension agents will be able to give you an idea of how much different labs charge for the testing service. Buying your own kit may be less expensive than sending soil in to a lab, but may not give you as detailed results.
There are a few important steps to follow when preparing soil samples for testing:
- Remove any surface debris, such as leave, twigs, and pine needles, before digging your sample
- Sample to a depth of about 6-8 inches
- Samples are best taken with a soil probe or auger; if you do not have access to these tools a clean knife, spade, or trowel can work as well
- Mix each sample in a clean bag or bucket
- Take several samples of the same size from different parts of the garden
- Mark the location of each sample
- In planting beds, sample between rows to avoid fertilizer or other soil additives
Soil Improvement Techniques
The following techniques are often used by gardeners to improve the organic content of their soils. This organic matter is important for plants because it provides essential nutrients and increases the capacity of the soil to retain moisture. Adding organic material to sandy soils can increase nutrient levels while increasing the capacity of the soil to retain both moisture and nutrients, and adding it to clay soils can help loosen the soil to allow both roots and water to move through it.
How much organic matter you add to your soil will depend on its current composition, but it is best not to add too much to it at any one time. Too much organic mater can lead to large cracks in the soil that are left when it decomposes (a process called "shrinkage"). To learn more about these techniques and other gardening basics, check out our Online Resource Library.
Mulches are used by gardeners to moderate soil temperature, control weeds, and improve moisture retention. Inorganic mulches perform these basic functions, while organic mulches also help improve soil composition as they decompose. While inorganic mulches can be added any time of the year, many recommend that organic mulches should always be added in late fall or winter, so that they will help retain winter moisture, normalize soil temperature, and reduce the growth of weeds in the early spring. Organic mulches can be added any time during the growing season, however, and if added in the spring or summer they will still do a great job of reducing your watering and weeding time. Mulch should typically be spread across the surface of the soil to a thickness of 2 to 4 inches.
Does not control weeds well; very good for preventing erosion on new slopes
- Felt Paper
Provides good weed control and insulates by absorbing heat from the sun; is expensive and must be weighted to keep it from blowing away
Paper should be moistened before installation and covered with another mulch to hold it in place; provides excellent weed control, and should typically only be used between rows and on paths
Should be covered with another mulch to improve appearance, but provides good moisture retention and weed control; must be placed on soil in spring and removed in fall
Dark stones retain heat, light stones reflect heat; can be very expensive and is not effective at controlling weeds unless placed over another mulch such as felt paper
Retains moisture well; great for use under trees and shrubs
- Cocoa Hulls
Expensive to purchase, but should be spread no thicker than 1 or 2 inches, or else it will mold; will add nitrogen to the soil as it decomposes
- Coffee Grounds
Best used in container gardens; should be spread no thicker than 1 inch
- Grass Clippings
Grass should be dried before application, or can get matted and mold; add nitrogen to the soil
- Dried Leaves
Should be chopped with a mower or shredder before application; can be mixed with other materials such as peat moss to aid in composition and keep leaves from blowing off of beds
- Ground Oyster Shells
Do not insulate the soil well, but do act like lime and help reduce soil acidity
One of the best mulches for the price, straw decomposes rapidly and does a great job of insulating soil over the winter; avoid oat straw or hay, which may lead to weed problems
- Pine Needles
Low-cost when pine trees are nearby; very good mulch for acid-loving plants
- Saw Dust
Low-cost mulch, but decomposes slowly and robs soil nitrogen; high carbon content
Compost is a powerful soil additive that can do much to improve soil fertility and plant productivity, and it is one that can be produced cheaply and effectively in your own garden. Compost is also friendly to the environment, because it is created from waste materials from the kitchen and garden. Compost can be used as mulch, but is most often worked into the soil rather than laid directly atop of it, or it can be used in combination with other organic mulches.
Compost is created by collecting the right types of scraps from your kitchen and garden, and allowing them to decompose in a compost heap or bin. Check out our Project Gallery page for detailed instructions on how to build your own compost bin from a few simple and inexpensive materials.
Compost creation is a complex biological process, but you will be able to create great compost with the right balance of warmth, moisture, and mix of materials. There are many books and other resources that offer detailed instructions on how to create and use compost, but there are a few very basic rules that will get you on your way to creating what many gardeners consider to be "black gold":
- Make sure your pile has a good mix of ingredients - a diverse blend is needed for successful, well balanced compost
- To keep your compost healthy, do not include any clippings or yard waste that may contain chemicals such as herbicides, pesticides, or fertilizer
- When adding kitchen ingredients, leave out animal products, such as meat scraps, which can attract rats, but do add vegetable and fruit scraps and peels, egg shells, and coffee grounds
- Do not add any weeds that have gone to seed, which may later germinate in your garden
- Keep air flowing in your compost pile by turning the pile once a month or so (some bins rotate, making this job a bit easier)
- Bigger is better! More heat will be generated by a big pile (but try to go no bigger than 3 feet by 3 feet)
- Keep the right balance of moisture in your pile or bin - too dry, and the decomposition process will slow down, too wet, and the pile will begin to stink
Cover crops have been used by farmers for generations, and can be good option for gardeners whose garden soils may need improving. There are many different types of cover crops, but all cover crops will benefit your garden in a number of ways: increase soil organic matter, decrease soil erosion and compaction, increase nutrient and nitrate levels, suppress weeds, attract beneficial insects, and increase yield of the following crop. You should check with your local university extension agency to find out which type of cover crop is best in your region.
Cover crops are usually cheaper than applying organic material directly to the soil, particularly if you do not have access to large amounts of compost. Because cover crops take up valuable garden space, they may be best used when just starting out a new garden, particularly if you are starting a garden in a city lot that may not have high levels of organic mater present in the soil. Cover crops can also be used in winter months, however, and these will have to be sown in late summer or fall.
Cover crops can be tilled into the soil just before the plants go to flower, or the greenery can be cut off at ground level and laid on the soil to act as mulch. The growing season for some cover crops is as short as 8 weeks, and you can generally plant immediately after the cover crop has been cut or worked into the soil.
Types of Cover Crops:
Some crops can be considered both summer and winter crops, but it is best to check with a local expert to find which will be most effective for your climate. Seeds can be obtained cheaply from online seed companies such as Johnny's Selected Seeds, High Mowing Seeds, and Pinetree Garden Seeds.
- Italian rye
- Hairy Vetch
- Winter Rye
- Hairy Vetch
- Field Peas