The start of each new growing season usually brings up discussions of how to start plants, prepare the soil, and provide an optimal plant growth environment. Questions surrounding what to do and what not to do can seem overwhelming. Know that there is usually no ONE right way. In the end, you will find your way through your own experiences and observations; that is what makes farming so beautiful! We hope that our observations, experiences, and insights will provide value to you in some way.
Watch our introduction video & which will give you an overview of this guide.
From the very start of a seeds’ life until it becomes a plant and is harvested, soil plays an important role in any plants development. Good potting soils provide seeds a place to germinate, form into seedlings, and develop into baby plants ready for the garden. A healthy and prepared garden soil then allows them to thrive. We’ll walk you through what we’ve found helpful when deciding which media to use for potting soil and how to prepare a garden soil for the transplants.
When starting out, many gardeners and farmers alike rely on bags of potting soil, readily available at your local nursery, hardware store, and elsewhere. Most certified organic types offer an excellent place to start and work quite well. We’ve found that most bags labeled “compost” or “topsoil” are often full of wood chips or just poor quality soils with little value. We avoid these by themselves, but we may work specific bagged compost into a mix. There are, however, general qualities any good potting soil should have. It should drain well, be lightweight, and have the ability to hold nutrients and moisture even in the heat. Taking the time to either make or buy a good quality potting mix is always a worthwhile investment.
The most common core ingredients found potting soils are fine sphagnum peat moss, coconut coir, perlite, vermiculite, compost, and sometimes granular fertilizers and ground limestone. Most mixes have variations of these components.
Sphagnum Peat Moss
Peat moss is a natural product harvested from bogs. The manner and rate of peat moss harvest continue to be a topic of much debate as many bogs have been destroyed or badly damaged during harvest. It is acidic, retains moisture well, and helps break apart other soils and mixes.
The byproduct of coconut harvesting, coco coir, is made from the fibers on the outside husk. It has a neutral PH 5.2, and 6.8 is one of the better ingredients for its water-holding capability, air space, and good drainage. A blend of sphagnum peat moss and coconut coir makes for an excellent potting soil base.
Perlite is a naturally occurring volcanic glass mined and then heated up until it expands into round, white particles. In potting soils, its primary function is to break up the soil and allow for air movement, but it also helps retain moisture too, just not as well as vermiculite.
Vermiculite is also naturally occurring and, like perlite, is heated up and expands into form when processed. In potting soils, it is renowned for its water-holding capabilities, but it also helps with aerating the soil, not to the extent that perlite does. Vermiculite varies in particle size depending on the grade and intended use. Small and medium-sized particles are commonly used for making potting soils.
Compost consists of decomposed organic matter and, when used in potting mixes, should be free from chunks of wood chips, bark, or other bulky materials. We like to sift our compost thoroughly before adding it to potting soil mixtures. It does make a great addition to potting soils as it usually has a neutral PH and provides an abundance of nutrients and helps to retain moisture.
Granular Fertilizers and Ground Limestone
When adding granular fertilizers to potting soils, the most common organic amendments are blood meal (for nitrogen) and bone meal (phosphorus). In general, nitrogen is essential for foliage growth and phosphorus for developing strong roots and also flowering. Ground Limestone comes from crushed up limestone or chalk. It helps to neutralize soil PH by reducing soil acidity through increasing alkalinity.
How the Ingredients Work Together
Sphagnum peat moss and coconut coir are used interchangeably with coir being better for retaining moisture and having a neutral PH (not acidic like peat). Some mixes are peat moss based and some are based using coco coir. Coir is hands down the better of the two if you were only to use one, but we like to blend the two and have found that this gives us a level of control for managing moisture retention. During the fall and spring seasons, we use a balanced mixture of peat and coir, whereas in the summer when the trays dry out more quickly, we use less peat (35-40 %) and incorporate some fine compost to go along with the coco coir to make up the other 60-65%. Whether you choose to blend the media or use them separately, they make up an important part of nearly all potting soil mixes.
Perlite and Vermiculite are also used interchangeably with perlite being better for aerating soils and vermiculite better for retaining moisture. Like with the peat moss and coco coir, mixing these two elements together can allow a grower more control over the media. You can add more vermiculite to the mixture to increase moisture retention in the mix, or use less to decrease it some. Using vermiculite when using many small cell trays can really help keep them from drying out and also is much easier to work with than perlite. Either way, whether using them together or independently, perlite and/or vermiculite are vital to a good potting mix.
Depending on how long you plan to keep your plants in cell trays, you can also add ground fertilizers and ground limestone to the mix. When preparing larger cell flats for plants that will be in them for a longer time (like tomatoes or peppers), it is important to either add granular food to the potting mixture or provide a liquid fertilizer. Bottom line is, once the plants really start growing, they’re hungry and will need food. We try to get most of our transplants out into the garden as soon as possible to avoid having to use much granular fertilizer in our potting soils. Ground limestone is also commonly added to potting soils that will be holding transplants for a while.
For a basic mixture, mix 1 part peat and/or coco coir to 1 part perlite and/or vermiculite. Adjust the mixture to retain more water by increasing the amounts of coco coir and vermiculite. Since this mixture does not have a lot of nutrients in the potting soil itself, make sure to provide the seedlings with a liquid fertilizer once they have put off their first mature leaf.
For a complete mixture, mix 13 gallons peat moss and/or coconut coir with 8 gallons of perlite and/or vermiculite, 7 gallons sifted compost,1-2 cups blood meal, 1 cup bone meal and ½ cup ground limestone. A complete potting mix like this is packed with enough nutrients and minerals to allow your plants time to develop before being transplanted.
Here, we are sifting a mixture of peat moss and coco coir.
During the shoulder seasons (fall and spring), we have not found it as necessary to add much compost to the mixture. Moreover, with the extreme humidity we experience, compost being added to the mix can sometimes create issues with too much water retention. It is important to really observed the moisture levels of the transplant trays with temperature and moisture fluctuations.
If you are getting ready to start a new garden plot, the depth of the topsoil will be an important factor to consider to ensure you’ll have enough soil depth to work with. Some soils may have a very shallow topsoil profile (2-4 inches) before hitting the subsoil. Check to make sure you have at least 6-8 inches to work with minimum, or bring in bulk topsoil to help build up your beds.Topsoil is important because it is made up from decomposed materials, is full of minerals (from rocks) and has sufficient air and water. It varies significantly in its composition from place to place. To see what elements your soils are composed of, try using the mason jar test below.
If we are looking the components of soil, we take into consideration the soil type (sand, silt and clay) in addition to the percentage of organic matter. The organic matter percentage can be greatly changed with regular applications of compost, but the original soil type will also have an effect. A simple way to know the composition of your soil is to take a mason jar (or some other transparent container) and put a few inches of soil in it. Then, fill the container with water and add a teaspoon of dish detergent. Shake well and let it sit for a day or so. After you’ve given time for the soil to settle, you should be able to see some layers formed. The top layer will show the amount of clay, while the middle layer will show the amount of silt and the bottom layer the amount of sand. This neat little experiment is fun to do and provides valuable insight into the characteristics of your soil. We came across this experiment in J.M’sThe Market Gardener and loved the practicality and simplicity of it. It is widely known and there are a number of videos available of people doing this experiment. Check it out here for a video demonstration.
In general, sand refers to the largest particles in your soil, while the clay refers to the smallest, and the silt is in between. Sand and silt help soils drain water well but they don’t hold many nutrients. While sand is almost completely void of nutrients, silt is able to hold some nutrients and also helps the sand and clay mix together
Clay is very compact and soils high in clay can get crusty and make it hard for the soil to breath. However, it is loaded with nutrients and also contains valuable minerals, including calcium. These soils can be difficult to work with physically, but through adding organic material they can become very rich and release many of the mineral and nutrient compounds. They also and hold water well which can be a benefit during scorching summer months.
The idea soil is a balanced loam, which consists of 50% (or less) sand, between 30-50% silt and between 10-25% clay. The ranges show variation in the possible structures for loam soils, but in general loam soils do everything right. They are rich in nutrients, retain moisture well but also drain well. Most soils are not a perfect loam, but through consistently working organic matter into your soil, over time your soil will become more loamy. It takes time and for many growers, it is a gradual process.
When most people think of soil testing, the local county ag extension center or an independent lab often come to mind. However, if you haven’t managed to get it done yet, don’t let that keep you from getting started yourself. Local nurseries and garden centers usually have inexpensive soil testing kits enabling anyone to get started right away, without waiting around for laboratory or ag extension agency results. A simple soil test will give you a baseline to work from.
We have a small market garden and took an alternative approach, bringing in bulk loads of topsoil (already tested) to essentially help build up beds on top of our existing ground. This approach gives us a somewhat controlled platform to begin our soil building process although it is extremely labor intensive and has increased our start-up costs substantially.
Soil testing is readily available through your local county extension agency. They have the boxes for the soil samples and will usually deliver it to the state agricultural department for testing. This is a great option when getting started; it’s the cheapest and most common if you’re not doing it yourself. However, we’ve ran across a number of growers who have found inconsistencies with using state soil tests or have found them lacking, and prefer independent labs operated by soil scientists.
When asking for professional assistance with soil science, we like to defer to the professionals with real farming experience. In doing so, we have been able to provide a holistic Fertility Management Service (FMS), with custom soil and water testing along with recommendations that are easy to implement and help balance soil fertility. Even if there is nothing that is obviously awry with the soil, getting a detailed analysis of how to improve production (and profitability) is a worthwhile investment.
Just as he human body needs nutrients to grow and live a healthy life, plants also do; nutrients nourishment both human and plant life. For example, the protein needed for growth and health in a human diet parallels the nitrogen needed in a plants diet. They are both are building blocks for life. In the world of plants, nutrients are divided into three categories: macronutrients, secondary nutrients and micronutrients. Macronutrients refer to the Nitrogen (N), Phosphorus (P) and Potassium (K) availability in your soils. Secondary nutrients are comprised of calcium, magnesium and sulfur, while micronutrients refer to elements like zinc, boron, iron and copper.
NPK refers to the availability of macronutrients Nitrogen (N), Phosphorus (P) and Potassium (K) in your soil.. A simple soil testing kit provides a good platform to know if there are any major deficiencies. It is also good to keep in mind that macronutrient levels can be changed quite easily through adding compost along with other amendments.
One of the big advantages of soil testing is that it allows the farmer to use appropriate amounts of fertilizers when preparing the soil. Without a test, it is easy to either over-fertilize or under-fertilize crops. It can save a farmer quite a bit of money (and headache) in the long run.
Soil PH is something we most certainly keep an eye on. Unbalanced PH levels and hinder your plants from fully using the nutrients and minerals that may otherwise be available in your soil. In other words, even seemingly rich soils with unbalanced PH levels (either too alkaline or too acidic) can pose challenges for plants.
Many simple soil PH testers are available at local hardware stores, nurseries and many other places. They’re not hard to find, pretty cheap and do a good job giving you a snapshot look at the soil PH. It’s a good idea to get one of these testers if you don’t already have one. They can be used to monitor soil changes that occur as you add organic matter and other amendments. If you’ve had your soil tested by an agricultural service or lab, the PH levels will be included in the reports.
When thinking about amending garden soil, it helps to view the soil as if it were alive because it is! A living and vibrant soil full of microbial life will nearly alway produce healthy plants and an abundant harvest. Living soil that is full in organic matter also requires less watering than other healthy soils. Bottom line, when initially preparing beds, it’s not a bad idea to go a little overboard with the compost.
Adding good, high quality organic matter is an important part of maintaining high soil fertility, especially if you turn beds over frequently. Many farmers refer to organic matter as the ‘engine’ that runs the farm. Through continually adding organic matter, the soil quality improves over time; it’s somewhat of a long term investment with an immediate kickback. We see it as adding energy and life back to the soil, recharging it in a way. Adding organic matter provides a home and a source of fuel for soil organisms, crucial for biological activity.
Soil microorganisms help break down and mineralize important nutrients, making them available for plants to absorb and use. Simply put, soil organisms help your plants make the most out of what your soil has to offer. Through adding healthy amounts of organic matter and taking care of the soil composition (through either no-till or low-till practices), the soil biology will continue to grow and improve.
Just like people, soil needs to breath; it needs oxygen. When soil becomes excessively wet (doesn’t drain well) it suffocates from a lack of oxygen. This can also happen when soil becomes crusty or is too full of clay. We use a broadfork to loosen the soil and this helps aerate the soil, but tilling also works well. Adding enough organic matter will help keep soils from becoming too packed down, and mulching when the plants are in the ground also protects clay soils from becoming too crusty.
Fertilization is an integral part of any successful garden and for us it starts when the plants are sill in the cell trays (before transplanting). As soon as the seedlings have shown their first mature leaf, we give them a boost with a liquid nitrogen fertilizer to promote foliage growth. We commonly to use diluted liquid fish emulsion which is cheap and easy to find locally at hardware stores, nurseries and many other places. For those who may not like the smell of fish fertilizers, there are usually other water soluble varieties readily available.
Prior to transplanting, preparation of the garden beds is important and for us varies based on the crops we plan to grow. For example, when preparing lettuce beds (or other greens) we will mix more blood meal, a natural nitrogen amendment, into our compost application. When preparing beds for onions, carrots or other root crops, we will add bone meal (a natural phosphorus amendment) into the compost to help with root growth and development. We also use alfalfa meal, a good source of Nitrogen (N) and Potassium (K), to help maintain soil fertility. There are also a number of dried manures available, and sometimes we’ll incorporate some Black Hen (poultry manure) into the mix for heavy feeders like tomatoes. It is important to remember that each farm and garden varies in its soil fertility, so there is no ‘one size fits all’ approach. A good approach when it comes to preparing the soil for transplants and fertilizing naturally is to see what is readily available locally. Most hardware stores and nurseries carry a wide assortment of natural fertilizers.