A Guide to Organic Soil Amendments and Fertilizers for Raised Garden Beds

By David Kessler
Published: April 16, 2018 | Last updated: April 29, 2021 09:41:59
Key Takeaways

Raised garden beds are a good choice for areas that lack healthy, rich soil.

Source: Korzeniewski/

The idea of planting a garden can be daunting for the beginner gardener. There is so much information and advice out there, as well as countless products and additives to choose from, it might feel like you need a PhD to grow a tomato.


The fact is, everyone can easily grow an edible garden. Similar to buying real estate, the most important choice a gardener makes is location. You cannot grow sun-loving plants, which most vegetable and fruit plants are, in dense shade. Most vegetables (excluding leafy greens like lettuce and cabbage) require a minimum of six to eight hours of direct sunlight per day.

Most of us can find an area that gets enough sun, but what are you to do if the area with the correct sun exposure does not have healthy, rich soil? The answer is simple: build a raised bed garden.


The Raised Bed Garden

Raised bed gardens have several advantages over traditional in-ground gardens. First, raised bed gardens are constructed above ground, lending themselves to easier planting, tending and weeding.

Raised beds are little more than large container gardens and can be placed anywhere, regardless of the quality of soil underneath. Also, raised bed gardens are ideal for square-foot gardening. You can build them out of wood—just don't use pressure-treated wood as the chemicals in the pressure treated wood can leach into your soil and your plants—or buy a raised bed garden kit.

Another option for someone who doesn’t have the time or tools to build one is to use a large fabric aeration pot. Aeration pots are fabric containers that come in sizes ranging from 1 to 300 gal.


These pots prevent the plant’s roots from becoming root bound, while encouraging a more robust root system with greater surface area in contact with the soil for improved nutrient absorption.

Once you have built your raised bed or purchased an aeration pot, now comes the all-important choice of what to fill it with. I prefer a high-quality potting soil that is loaded with organic fertilizers and micro-organisms.


If that does not fit your budget, a less expensive option is topsoil, which is sold by the bag at every hardware store or sold by the truckload. It can be used as base for your garden soil, but topsoil is not ready-to-use just yet. When buying topsoil, make sure it has been screened, ensuring that large pieces of organic debris and rocks have been removed.

Raised Bed Garden Fertilizer

Plan on adding organic matter and organic fertilizer to the topsoil to guarantee a bountiful harvest of your favorite fruits and vegetables.

The best way to add organic matter to soil is by adding a rich compost. Compost is decayed organic matter, and it is one of the best things you can add to any soil. You may have the notion that a compost pile is a big, ugly, smelly pile of leaves and lawn clippings, but that is not necessarily true.

Today people have different home-made compost piles, well-constructed compost bins and stylish compost tumblers. These provide everyone with the option of making their own nutritious organic soil inexpensively. You can also improve the soil structure, moisture retention and drainage of your garden soil with the addition of products like perlite, shredded leaves, peat moss, coconut coir and composted bark sold as soil conditioner.

Aside from compost, there are several organic fertilizers and additives that can be added to improve your garden soil. One popular option is composted animal manure. There are several kinds to choose from including: seabird guano, bat guano, cow manure, horse manure and chicken litter.

Generally, manures from animals with a vegetarian diet are preferred to animals that eat meat. Animal manures vary greatly in the nutrition they will provide your garden due to these different diets.

When possible, it is best to use composted manures and guanos in your soil; fresh manure is best placed in your composter to age and break down before it is used or you risk burning your plants.

An added benefit of animal manures and guanos is that they provide an excellent source of beneficial micro-organisms, which add to your soil’s ecology. You can also add beneficial fungi and bacteria.

Other options for amending soil include the following organic fertilizers and additives:

Rock Phosphate

A natural, granular source of phosphorous and calcium in addition to several trace minerals, rock phosphate promotes cell division, photosynthesis and respiration. Rock phosphate also encourages the growth of earthworms and soil bacteria that enrich and aerate the soil and it is a slow release product, so it will not leach away like chemical blossom boosters. Apply 1 to 3 lbs. per 100 sq. ft. of garden.

Blood Meal

A slow-release, organic nitrogen source. Excellent as a top dressing when extra nitrogen is needed. Stimulates bacterial growth. Use 2 to 3 lbs. per 100 sq. ft or as a top dressing.

Bone Meal

Steamed, finely ground bone provides phosphorus, calcium and nitrogen and promotes strong, vigorous bulbs, healthy root systems and good blooming. Excellent for flowers, roses, garden bulbs, shrubs and trees. Use up to 5 lbs. per 100 sq. ft.


Greensand contains 22 minerals and helps loosen compacted clay soils. Highly recommended for conditioning pastures, lawns, orchards, fields and gardens. Apply 2 to 4 lbs. per 100 sq. ft.

Worm Castings

A pure, all-natural plant food produced by earthworms, worm castings help to develop foliage in plants and improve aeration of the soil. Worm castings are also a source of nitrogen. Use in gardens and flower beds at rate of a half cup per plant every two months. In potting mixes add 1 part earthworm castings to 3 parts soil. For roses, mix 4 cups into the soil around each plant.


Sulfur is excellent for lowering the pH of soils for growing blueberries, rhododendrons, azaleas and other acid-loving plants. Use according to soil test recommendations—do not over apply. Maximum use: ¼ lb. per 100 sq. ft.

Micro Pelletized Gypsum

Pelletized calcium sulfate supplies calcium and sulfur while loosening clay soils, aiding aeration and water penetration. Use when calcium and sulfur are needed, and pH of the soil is alkaline. Use 2 to 3 lbs. per 100 sq. ft.

Garden Lime

Garden lime is a natural liming material that supplies additional calcium and helps maintain a near-neutral pH in your soil. Apply 3 to 5 lbs. per 100 sq. ft.

Once you have built your bed, added your soil and amended it with lots of organic matter and fertilizer, it is time to plant your seeds or seedlings. Starting seeds is easy to do with a seed starting kit.

Another option is to visit your local nursery and buy vegetable seedlings. Ask retailers for what varieties will perform best in your area. Water regularly (as needed) and top dress around the base of your plants on a monthly basis to ensure your plants have plenty of food. You will be eating your harvest in no time.


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Written by David Kessler

Profile Picture of David Kessler
David Kessler heads research and development at Atlantis Hydroponics and writes for their popular blog. David has more than two decades of experience and multiple degrees from the State University of New York. An accredited judge for the American Orchid Society, he travels the world judging events. Follow his blog at

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