Bone Meal as a Plant Fertilizer: What You Need to Know

What is Bone Meal?

Bone meal is a type of organic fertilizer made from steamed animal bones that are ground into a fine powder or granules for application on plants or crops. The most commonly found form in most garden stores is a finely ground powder with a consistency similar to baking flour.

Bone meal fertilizer is an excellent source of phosphorus, which is essential for plant growth and development. Bone meal is a slow-release form of phosphorus (P) that may be expressed as phosphate or phosphorus. Phosphorus as a percentage is 2.3 times higher than numbers shown for phosphate, so 10 per cent phosphate is the same as 23 per cent phosphorus.

Bone meal is also rich in calcium, which helps to strengthen cell walls and improve plant structure.

How Do You Use Bone Meal as a Plant Fertilizer?

Bone meal can be incorporated into soils at a rate of 10 pounds per 100 square feet of garden.

Most plants will benefit from an annual application of bone meal, including flowering plants such as cannabis, but it is particularly beneficial for root crops, including carrots, onions, radishes, parsnips and turnips. Flowers grown from bulbs, corms and tubers will also benefit from an application of bone meal. (Read also: 4 Easy Steps to Super Soil for Thriving Cannabis Plants)

The calcium infusion from bone meal helps plants develop strong and healthy cells and seeds. It also strengthens the stems and aids in the development of new shoots in perennial crops and shrubs. The calcium in bone meal can also help prevent common problems in vegetables such as blossom-end rot in crops like tomatoes, eggplants, and peppers.

Bone meal can be used as one part of a balanced organic fertilizer program for plants that benefit from a slow-release form of phosphorus. It can feed plants for up to four months.

Although it does not offer a high amount of either, bone meal also has trace amounts of nitrogen and potassium.

Here’s when to add bone meal to the garden—and when not to.

Bone Meal for Phosphorus

All plants need phosphorus, which bone meal supplies, especially when developing roots. It is one of the three essential macronutrients, along with nitrogen and potassium. Adequate amounts of phosphorus in the soil are essential for optimal crop yields.

In addition to root development, it enables plants to store and transfer energy, and develop flowers and fruit. Maximum phosphorus availability occurs between pH levels of 6 and 7.

A phosphorus deficiency may present itself on the plant as stunted growth, and weak or spindly stems. Phosphorus-deficient leaf symptoms include dark leaf veins while the rest of the leaf fades to hues ranging from yellow, purple or blue-green. Flowers may be underdeveloped, appear late, or not at all.

Other organic or natural sources of phosphorus besides bone meal include rock phosphate and manure from herbivores. (Read also: The Importance of Phosphorus for Fruiting Plants)

Bone Meal for Calcium

Calcium is a naturally occurring secondary nutrient needed by crops for plant growth. Plants use calcium from bone meal and other sources to produce cell walls and root ends. Calcium deficiency shows itself in the roots, leaves and fruits of plants, although it may be hard to detect if it is only affecting the roots.

In leaves, the young leaves are affected first and will appear slightly deformed. Severe calcium deficiency will kill growth tips and stop leaf production entirely. Roots become stunted and short, and are not vigorous enough to penetrate through the soil.

Calcium-deficient fruit may develop blossom-end rot, which causes the blossom end of the fruit to become dark, leathery feeling and looking, and eventually rotten. Affected fruit will stop growing and drop off the plant.

For nitrogen-fixing legumes, calcium deficiency will appear as pod rot, and the plants will not fix nitrogen as efficiently as those that are well supplied with the mineral.

Certain regions in the United States are more prone to calcium deficiency than others. In the Northwestern and Eastern states, calcium is readily leeched out of the soils from rainfall and irrigation.

The precipitation soaks into the ground and pushes the calcium from the upper layers of the topsoil downward. Other regions with large compliments of limestone, gypsum or apatite are usually high in calcium. Coastal states with coral or marine shells in the soil tend to be rich in calcium as well, particularly calcium carbonate.

Other organic and natural sources of calcium include eggshells, gypsum and lime, although lime should not be used on soils that have a pH higher than 7. Adding too much calcium to your soil can raise pH levels, making soil more alkaline.

Many food crops can be harmed by additives that raise the pH too high. If you need to add calcium and also raise the pH, limestone should be considered instead of bone meal. If you need to add calcium, do not need the phosphorus boost of the bone meal, and do not wish to raise your soil pH, gypsum (calcium sulfate) should be used. (Read also: 5 Reasons to Add Calcium Carbonate to Your Garden)

Precautions When Adding Bone Meal to Your Garden

As useful as bone meal is, it may not be a panacea for phosphorus-starved soils or plants. Recent research from Colorado State University suggests phosphorus from bone meal is only available to plants in soils that have a pH below 7.

For alkaline soils, research shows it is best to use composted or vermicomposted manure as a source of phosphorus. Soils with a pH level of 7.5 and above often have high calcium concentrations that tie up phosphorus as calcium-phosphate. Calcium phosphate is an insoluble compound not available to plants.

Over-application of bone meal can have negative effects on plants and the surrounding environment. Most soils contain some quantity of natural phosphorus, except for soils that have been farmed for several successive years.

Too much phosphorus will continue to promote root growth, but in excess, it interferes with the roots’ relationships with mycorrhizal fungi. Without the mycorrhizal fungi, the roots have a more difficult time developing and using the nutrients that surround it.

Phosphorus runoff, though much more prevalent with synthetically produced phosphorus than the form found in bone meal, can hasten the eutrophication of nearby waterways. Eutrophication is the emergence of undesirable algae and underwater weeds that grow as the result of the increased nutrient supply.

As the biota die and decompose, bacteria consume dissolved oxygen, resulting in oxygen shortages in the water bodies. It is important both economically and environmentally to apply only the amount of phosphorus required for your specific crop or soil.

When applied as a top-dressing, bone meal can attract dogs, raccoons, coyotes and other carnivorous and omnivorous animals. It should be well incorporated into the soil by tilling, raking or spading, and then watered in to leave as little on the surface as possible to avoid damage to your garden by scavenging animals.

Test Your Soil Before Adding Bone Meal

As a final note, before applying bone meal or any other amendment, know the pH and nutrient levels you have already. All of the amendments in the world, organic or not, will not do your crops any good if they are applied in toxic amounts.

Soil testing is easy and inexpensive. Do-it-yourself kits are readily obtained at most garden and home centers. These are not 100 per cent accurate, but do give you a good idea. For a few dollars more, you can send your samples to a lab to get a detailed analysis of what is in your soil.

Most will also include recommendations and a key to interpret the analysis. Most state universities have a lab, or you can consult your local extension service to find out what testing facilities are close to you.