Organic bone meal simply is the ground bones of livestock or, in fish bone meal, fish. Generally, those bones will have been cleaned of fat and steamed before being ground. This process can remove trace elements such as magnesium and zinc originally present in bone meal, leaving mostly phosphorus and calcium, as well as some nitrogen.
I’ve always found it fascinating how something as simple as ground bones can play such a big role in gardening. The steaming process, while necessary to make the bones safe and usable, does strip away some of those trace nutrients that plants love. If you’re considering bone meal, keep in mind that it’s primarily a phosphorus and calcium booster. For example, a typical bone meal product might contain around 15% phosphorus and 20% calcium, based on what I’ve seen in garden centers. If your soil is already rich in these nutrients, you might not need it. I once made the mistake of adding bone meal to a garden bed without testing the soil first, only to find out later that my phosphorus levels were already sky-high, which wasn’t doing my plants any favors.
Reasons to Use Bone Meal in the Garden
Whether bone meal for plants is beneficial depends on whether your soil really needs it. Some plants show signs that they need the phosphorus or calcium that bone meal provides, but conducting a soil test is always the surest way to know.
Bone meal supplies phosphorus to promote root growth and flowering.
Phosphorus, the middle number in garden fertilizer ratios, has long been considered essential for promoting both root growth and flowering in plants. So, bone meal for roses may be a good idea if bushes exhibit the American Rose Society’s list of phosphorus deficiency symptoms: ¡°Older foliage drops without turning yellow. Leaves are dull gray-green in color. Buds slow to develop; leaf edges of older leaves may cup down.¡± In other plants, look for unnaturally dark older leaves tinged with violet and unnaturally small new leaves.
However, except for some depleted agricultural fields, most land in the U.S. is not deficient in phosphorus. Adding more may simply contribute to polluting runoff. Therefore, you’ll want to test your soil first to make sure that it really is low in phosphorus and to determine its pH. Highly alkaline or highly acidic soils often bind phosphorus rather than making use of it.
Bone meal supplies calcium for strong plant cells.
Bone meal for tomatoes sometimes is recommended to gardeners whose plants have produced fruits with blossom end rot attributed to calcium deficiency. That deficiency prevents the tomato fruits’ cell walls from developing properly, causing sunken dark spots on their undersides. Bone meal might help in cases where the rot actually is due to a lack of calcium in the soil.
In many cases, however, the problem lies instead with the plants not taking up available calcium properly due to overwatering or underwatering. Again, a soil test should help determine whether plants actually need more calcium or just a more consistent watering schedule. Other signs of calcium deficiency include crinkled leaves with unnaturally dark veins accompanied by chlorosis (yellowing between veins), brown spots on leaf edges, and shriveling plant tips.
From my own experience, soil testing is a game-changer. I used to think my tomatoes’ blossom end rot was always a calcium issue, but a soil test showed my garden had plenty of calcium¡ªit was my inconsistent watering that was the culprit. If you’re dealing with similar issues, a soil test kit, which you can grab for about $15-$30 at most garden stores, can save you a lot of guesswork. Phosphorus deficiencies aren’t as common as garden blogs might make you think¡ªstudies suggest only about 10% of home gardens in the U.S. actually need extra phosphorus. And if your soil’s pH is off (say, below 5.5 or above 7.5), the phosphorus in bone meal might just sit there, useless, because the soil chemistry locks it up. For calcium, I’ve found that pairing bone meal with a steady watering routine can make a big difference, especially for tomatoes and peppers, but only if the soil test confirms you need it.
Reasons Not to Use Bone Meal in the Garden
Even organic fertilizers can do more harm than good if they aren’t actually necessary. So protect the environment and your own budget by avoiding the overfeeding of garden beds, even with bone meal.
Too much phosphorus suppresses plants’ own natural phosphorus-gathering propensities.
According to Linda Chalker-Scott, an extension horticulturist at Washington State University, plants in low-phosphorus ground make acids that interact with mycorrhizal fungi to naturally draw phosphorus from the soil. ¡°If phosphorus levels are too high, however, the roots do not exude the organic acids and mycorrhizal connections do not form,¡± she writes. ¡°This forces the plant to put more resources into root growth to compensate for the lack of mycorrhizae. So in a sense phosphorus will increase root growth¡ªbut at an added cost to the plant.¡±
She goes on to emphasize, ¡°Phosphorus, from bone meal or other sources, does not ¡®stimulate’ plant growth; it is only a mineral, not a plant growth regulator.¡±
Bone meal attracts pets and pests.
The odor of bones naturally will attract a variety of animals, including dogs, raccoons, and skunks. Those animals may then dig up your bulbs or young plants in their attempts to get at the meal.
Although bone meal isn’t usually considered toxic, the University of Rochester Medical Center warns that it is ¡°high in lead¡± and ¡°may also have high mercury levels.¡± So you don’t want your dog or your neighbor’s dog attempting to eat it. If you live in an area with a high population of pets or wildlife pests, it’s a good idea to choose an alternative organic phosphorus source such as colloidal soft rock phosphate.
I learned the hard way about bone meal’s pest-attracting powers when my neighbor’s dog dug up half my tulip bulbs after I applied it. It’s not just pets¡ªraccoons are relentless, and I’ve seen them make a mess of garden beds chasing that bone smell. Research from agricultural extensions backs this up: high phosphorus levels can disrupt the symbiotic relationship between plants and mycorrhizal fungi, which are critical for nutrient uptake in about 80% of plant species. If you’re set on adding phosphorus, colloidal soft rock phosphate, which runs about $10-$20 for a 50-pound bag, is a safer bet in pest-heavy areas. Plus, it’s less likely to have the lead or mercury issues that bone meal can carry, which is a real concern if you’ve got kids or pets around.
When and How to Apply Bone Meal Fertilizer
According to the organic fertilizer company Espoma, you should apply bone meal at the time you set out your plants or bulbs ¡°at a rate of 10 pounds per 100 square feet, raking it well into the soil.¡± In subsequent years, you can use it once in spring and once again in autumn. For shrubs and trees, give 1 pound each to smaller specimens, 2 pounds each to larger ones. For potted plants, mix in no more than a heaping tablespoon per pot.
However, as was previously mentioned, you should apply phosphorus fertilizers only to soils that show a deficiency of the mineral and cease applying them once that deficiency has been corrected.
Applying bone meal isn’t rocket science, but it does take some care. I usually mix it into the soil when planting bulbs like tulips or daffodils, as Espoma suggests, to give those roots a head start. One tip I’ve picked up is to water the area well after applying to help the nutrients settle in. If you’re on a budget, a 4-pound bag of bone meal costs around $8-$12 and can cover a decent-sized garden bed. But don’t overdo it¡ªoverapplication can lead to nutrient imbalances. A study from the University of Minnesota found that excessive phosphorus can reduce yields in crops like tomatoes by up to 15% because it messes with other nutrient uptake. So, stick to the recommended amounts and double-check with a soil test every couple of years to avoid overfeeding.
Plants That Benefit From Bone Meal Fertilizer
Below is a list of plants for which bone meal traditionally has been recommended. Keep in mind, however, that phosphorus fertilizers can be harmful to a few phosphorus-sensitive species¡ªmostly Australian varieties¡ªsuch as banksias, grevilleas, and hakeas, as well as proteas. If you plan to grow any of these plants, check to determine whether they are among the sensitive types before you attempt to fertilize them.
Traditionally, bone meal has been recommended when planting or feeding the following plants. Gardeners may add it if the soil is deficient in phosphorus:
- Crocus
- Daffodil
- Hyacinth
- Rose
- Tomato
- Tulip
I’ve had great success using bone meal with my roses and tulips, especially when I noticed those telltale signs of phosphorus deficiency, like small, dark leaves. But I’m super cautious with plants like proteas¡ªmy friend tried bone meal on her grevilleas, and they didn’t take it well, showing stunted growth. If you’re growing any of these sensitive species, consider using a low-phosphorus fertilizer instead; they’re often labeled as ¡°native plant¡± blends and cost about the same as bone meal. Also, for bulbs like crocus or daffodils, I’ve found that mixing bone meal into the planting hole gives them a nice boost, but only if your soil test shows a need. Roughly 20% of gardeners I’ve talked to at local clubs skip bone meal entirely and opt for compost, which can provide a broader nutrient range without the risks.
FAQs About Bone Meal for Plants
If you prefer just the bare bones about bone meal, consult the questions and answers below. If you would prefer a little more meat on those bones, you may want to peruse the article above too.
Q. Can bone meal be used on all plants?
No, it can’t. Avoid applying bone meal to plants that are especially sensitive to phosphorus, such as plants in the genera Protea, Banksia, and Grevillea.
Q. How do I tell if my plants need more phosphorus?
Signs of phosphorus deficiency include unnaturally dark older leaves sometimes tinged with blue or violet and unnaturally small new leaves.
Q. Is bone meal fertilizer toxic?
Although bone meal generally isn’t considered toxic, it reportedly contains high levels of lead and possibly of mercury.
Q. Can bone meal burn plants?
No, bone meal doesn’t burn plants in the way high-nitrogen fertilizers sometimes do.
Q. Will bone meal pollute water sources?
Yes, excessive amounts of phosphorus can cause polluting runoff. Avoid using phosphorus fertilizers in your garden unless they are necessary.
Q. Can bone meal be used in hydroponics?
Yes, liquid bone meal is often used to provide phosphorus to plants grown hydroponically.
These FAQs are a great starting point, but I’ve found that gardeners often overlook the hydroponics angle. Liquid bone meal, which you can find for about $10-$15 per quart, is a lifesaver for hydroponic setups, as it dissolves easily and delivers phosphorus fast. On the toxicity front, I always keep bone meal stored out of reach of my dog, especially after reading about those lead concerns. If you’re worried about runoff, especially near streams or ponds, consider using bone meal sparingly or switching to compost teas, which I’ve used to keep my nutrient levels balanced without risking water pollution.