It's pretty rare to start a garden out with rich, perfectly balanced soil. Most of us have to work at it. Knowing your soil fertility levels can make a big difference in your plant's productivity and health, though, so it's vital to get it right. Don't let all that talk about alkaline soil and phosphorus deficiencies overwhelm you. We've created the foolproof guide to improving your soil's fertility without breaking the bank.
Why is Soil Fertility Important?
When I purchased my current farm in October of 2006, it was land that had been used as a back cow field. The first thing I set out to do was plant an orchard. I was excited and could not wait to get my newly purchased trees in the ground.
But typical of my region, all of that colorful green sod covered a small amount of topsoil and lots of clay soil intermingled with limestone rock. In some places, I sank my shove just to hit hardpan.
I went into my small town and purchased peat moss and compost at the local garden store and mixed it into the soil around the roots. That quickie solution got me through the first planting, but I knew I had to do something more for my soil's fertility if I wanted my gardens to flourish.
Soil Fertility is the Secret to Healthy Plants
Having healthy soil is essential if you want healthy plants. Like you, your plants need to proper nutrients to grow and prosper. Unlike you, your plants can not relocate if they are not getting what they need.
Plants have three primary nutrients: nitrogen, phosphorus, and potassium. When you see NPK on a fertilizer packaging that's what those letters mean.
Flora uses nitrogen to promote cell division and growth. It's what helps them develop green leaves, which are important because they soak in sunlight and produce energy. We also eat the green leaves of many vegetables like lettuce and kale.
Phosphorus is what your plant needs to produce flowers and fruits. If your tomato plant is all leaves and little fruit, then you may need phosphorus.
Potassium promotes healthy roots and to help plants fight off diseases. It's is especially important for root crops like carrots and beets.
Secondary and Micro-nutrients
NPK are called macro-nutrients because they are considered the most important to plant growth. Interestingly, carbon, oxygen, and hydrogen are also considered macro-nutrients, but luckily, we don’t have to buy them.
Secondary nutrients are also vital for soil fertility, and gardeners sometimes neglect them. They are calcium, magnesium, and sulfur.
Calcium regulates the flow of nutrients in a plants body. If a plant is stunted, it may have a calcium deficiency. You are probably familiar with blossom end rot on tomatoes which is caused by not enough calcium or poor calcium absorption.
Magnesium is critical in photosynthesis and helping your plant make food for itself.
Sulfur is an element necessary in enzyme reactions and protein synthesis, which helps with plant growth and seed development.
Micronutrients such as boron, iron, and zinc are needed at smaller levels but are still essential for the plant.
What is pH?
The acidity and alkalinity of your soil, otherwise known as the pH level, influences plant health and yields. pH stands for “potential of Hydrogen,” and it refers to the correlation between hydrogen and hydroxyl.
Soil pH is measured on a scale of 0 – 14. Anything at zero on the scale is extremely acid, and 14 is very alkaline, with 7 being neutral. The best range for most garden plants is 6.1 to 6.9.
That said, some plants do like extremes. Blueberries and azaleas are famous for needing soil that is more acid. Asparagus prefers a more alkaline soil.
Garden soil pH level is an essential factor in your soil fertility plan because it affects many aspects of the garden including the soils structure, nutrient availability and bacteria in the earth.
You want healthy bacteria because they break down organic matter and make nutrients available for the plant. Fortunately, beneficial bacteria prefer a similar pH to your plants.
Figuring out your ground's balance is crucial if you want your plants to thrive. To get an idea of your soil's composition, you must take pH measurements and balance your earth if necessary.
Garden soil testing is useful because it gives you feedback in the form of numbers to determine what levels of nutrients your soil has.
I know math can be intimidating, but never fear. All you need to do is plug your numbers into an average chart to see where your soil fertility stands.
In fact, many companies give you an average and show you if you are deficient. As you can see in the picture below my earth in G2, the garden by my barn, was deficient in Calcium. It shows up as 191 below the average.
I corrected that imbalance by adding gypsum, which I chose because it adds calcium without impacting the pH of the soil. As you can see my pH was 6.6 – a good number, so I didn't want to mess with it. Figuring out how to amend your earth without changing the good elements is the trick to establishing healthy soil fertility.
For instance, let's say I was low in calcium and had a pH below 6.0. Instead of gypsum, I could have added limestone. Limestone adds calcium in addition to raising the pH level.
Where Do I Get My Soil Tested?
Many county extension offices offer low-cost soil fertility testing for $10-20. I think the investment is well worth the dividends you will reap when your plants start thriving.
Online laboratories will do a test. Soil tests from a laboratory are usually more extensive than those offered by the extension service. The costs will run you from $25 – $55 depending on the tests you want.
You have the option of purchasing a DIY kit online and testing your soil. A word of caution with these: I would recommend if it is your first time getting a test that you send it to an online lab or county office because they will be more accurate. It's also nice to have your extension agent or the lab tech available if you have questions.
Speaking of soil fertility tests, you may have heard acidic earth called sour soil and alkaline called sweet soil. My grandfather and others of his generation would taste the earth. That was their way of “testing” pH and where we get the expressions the ground is sweet or sour.
You might get to a place where you can taste test your soil, but I'd recommend starting with one of the options above.
What Nutrients Should I Add?
You've gotten your soil fertility test results back, and now you know what nutrients you need. How do you go about deciding what to add? You can buy a complete mix formula or but I'd recommend getting raw nutrients to mix into your garden soil. That way you can tailor your mix to suit your earth.
The advantage of a complete mix fertilizer is that it is easy to buy and apply, but the disadvantage is that one size doesn't fit all. Complete mixes are often better used during the growing season for a boost.
Adding specific minerals and lots of compost is the way to go when your goal is long-term soil fertility. Fall is the perfect time to add amendments because the minerals and compost will improve your earth and make it ready in spring. As an alternative, you can add amendments in the spring before you get your plants in the ground.
Addressing Alkaline and Acid Soil
It's important to keep in mind that the pH of your earth can vary slightly over the year. You may want to test once in the summer and once in the fall to determine a general baseline.
You can lower alkaline or “sweet” soil by a point or more by adding gypsum (calcium sulfate) or ground sulfur. Sulfur works best in the summer and takes a few weeks to take effect. Make sure to mix it in thoroughly or you will have highly acid spots.
If you have slightly high pH, you can gradually adjust it by half a point over time by tossing in coffee grounds or compost that contains pine needles, which are acidic. You can also add compost or manure, which increases nitrogen and lowers pH over time. For a quicker fix, you can pour cold coffee diluted with water on your soil.
Acid or “sour” soil can be raised using dolomite lime. Don't use lime if your magnesium levels are average or high. Use eggshells, oyster shells, hardwood ash or calcite to raise pH instead.
When you get ready to adjust your earth, keep in mind that the amount of soil amendment you need to add will depend on what type you have. Sandy soil typically requires more amendments and fertilizer than heavy, clay soil.
Compost is a given – you should be adding it to your garden when you can. It's is a long-term soil conditioner, and it does so much for the soil. It contains microbes which add beneficial bacteria and fungi. Over time, it adds nitrogen, which can slightly lower pH.
Add raw manure to your garden in the fall. It will decompose during the freezing and thawing of winter and add nutrients to the soil. If you have dry weather, you can go ahead and till it in after you muck out the barn.
Worm castings are a rich source of fertilizer, and they allow plants growing in acid or alkaline soil to absorb nutrients better than they would be able to otherwise. Castings are neutral, so they don't change pH. Use about 7 pounds per 100 square feet of garden soil.
Rock phosphate is excellent if you are low in phosphorus. The finely ground rock powder improves your plant's root systems. Rock phosphate won't impact pH, but it works best in acid soils. Apply 10 pounds to your garden soil for every 100 square feet.
Add phosphorus to your soil using bone meal. Bone meal also contains nitrogen and calcium. It won't alter your pH, but it works best in soils with a pH below 7. Use 1 pound of bone meal per 100 square feet.
Turn to greensand for a great source of potash and micronutrients like iron. It's a workhorse in the garden and is a great soil conditioner. It helps to break up heavy clay and bind sandy soil which stops erosion and make nutrients more available. Greensand won't impact pH. Apply greensand at 5 pounds per 100 square feet.
Limestone raises pH and contains calcium and magnesium. You can raise your garden's pH by applying finely ground limestone. Apply about 3 pounds of limestone for every 100 square feet.
Some Other Around The House Soil Improvements
Hard Wood Ashes
If you have a wood stove or fireplace, you have excess wood ashes. What you may not know is that they are a great garden soil conditioner and an excellent source of potassium. Wood ashes will raise your soil's pH. They do contain salts so use it in small quantities.
You can lower your garden pH using coffee grounds. They are best used when planting fruits like blueberries. If you're not a coffee drinker you can often get leftover grounds from restaurants. Keep in mind that coffee grounds won't make a huge difference and they take time to work.
If you are looking for a cheap soil conditioner and to add lots of trace minerals, look no further than the leaves in your yard. Be sure to till leaves into the earth. If you don't till them in often, they become a hiding place for garden pests.
Taking the time and making some of these investments in your soil fertility will pay off in large dividends. Plants that are healthy have higher yields. A plant that is healthy will also cost you less time and money because they will be better able to fight off pests and diseases.