Fertilizing Your Garden Organically: The Basics + Some Natural Fertilizer Options

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When you use natural fertilizers to feed your plants instead of conventional chemical blends, you’re feeding the soil at the same time. You’ll see improvements in soil quality over time, the risk of fertilizer mishaps is much lower, and it’s a lot healthier for the ecosystem.  

Natural fertilizers work differently than the conventional kind. Once you get an idea of how they work together with soil life to supply nutrients to your crops, you can use them to their full potential to get awesome results and plentiful harvests.

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The Key Differences Between Organic and Conventional Fertilizers

First of all, the terms synthetic or chemical aren’t too accurate for describing non-organic fertilizers. ALL the nutrients plants need are chemicals, and those chemicals exist in nature. Calling them “conventional” fertilizers makes more sense.

At the chemical level, the nutrients available in organic fertilizers and conventional fertilizers are the same thing. The nitrogen you get from composted manure (organic) is no different from the nitrogen in ammonium nitrate (conventional). The big difference is in where those chemicals come from and how they’re processed into a form your plants can use.

The nutrients in conventional fertilizers are sourced from gases in the atmosphere, minerals, and sometimes even recycled industrial waste. Extracting those nutrients often takes some pretty complex chemical reactions.

For nitrate fertilizers, nitrogen is extracted from the atmosphere and converted into ammonia using heat, high pressure, and natural gas like methane. That ammonia is further processed into fertilizer products like urea and ammonium nitrate. To make conventional phosphorous fertilizers like superphosphate, manufacturers use sulfuric acid to strip rock phosphate down to a soluble salt. 

When we’re talking about fertilizers, the term “organic” means the nutrients come from a plant or animal source. Organic fertilizers are in a much more natural state, and they rely on soil organisms to break them down so plants can use them instead of chemical reactions in a lab setting. Any processing, such as drying, pelletizing, or heat-treating, is only done to make them shelf stable and easy to work with.

Why Use Organic?

Conventional fertilizers have some drawbacks and potential problems, both for the environment and on the smaller scale in your garden.

Because they’re so concentrated, conventional fertilizers are prone to leaching. When that happens, unabsorbed fertilizer “escapes” and contaminates waterways. This can cause problems like algae blooms in rivers, lakes, and oceans.

These fertilizers’ highly-concentrated state also makes them easier to over-apply, which can burn your plants or, at best, cause them to produce a bunch of excess leaves and not much fruit. Over time, heavy use of them can lead to salts building up in the soil, affecting pH levels and soil quality.

Feeding Plants Vs. Feeding the Soil

The nutrients in conventional fertilizers are instantly available for plants to take in, which sounds like an overall good thing. But when you bypass the natural process of soil organisms breaking down organic material to release nutrients, you miss out on a lot of benefits.

Organic fertilizers feed the soil life, first. As the beneficial microbes, fungi, worms, and other decomposers work on them, their increased activity improves the soil’s structure in big ways. Earthworm castings, secretions from soil microbes, and fungal mycelia aerate and loosen the soil, improving drainage and reducing compaction.    

While there’s no glaring evidence conventional fertilizers are directly harmful to soil organisms (honestly, it’s probably understudied), they won’t do much to help them, either. Using conventional fertilizers alone, you’ll probably find you have to add more to get the same results, over time. Organic fertilizers build rich, living soil instead. As your soil’s ecosystem thrives and grows, you’ll eventually need less inputs to grow healthy crops. 

Some Extra Benefits of Organic Fertilizers

-They have a more diverse nutrient profile. Since the target nutrients have been carefully isolated from their natural source during processing, conventional fertilizers don’t have any extra nutrients to offer unless they’re added at the factory. Organic fertilizers are raw materials. Most are full of bonus good stuff like trace minerals, micronutrients, and sometimes beneficial fungi and microbes.    

-They don’t need to be applied as often. When you apply a conventional fertilizer, plants will generally take in what they need immediately, and the excess nutrients are lost through runoff or leaching. Organic fertilizers release their nutrients slowly as the soil life breaks them down. That means your plants get a steady supply of nutrients for a longer period of time instead of one big dose.

Most conventional fertilizers need to be applied at least every other week. When we feed with a balanced organic fertilizer, we only need to apply it once or twice in a whole season.

-They may reduce pest pressure. Sometimes, feeding your plants with a conventional fertilizer can cause them to grow a little too fast. That big flush of tender new growth all at once can attract insect pests. Pushing plants to grow too quickly under less than ideal conditions, such as hot weather, can also cause plant stress, another factor that draws in pests. Organic fertilizers promote healthier growth at a more natural rate.

-They’re safer to handle. Conventional fertilizers can be quite caustic and can cause chemical burns on skin. They pose a danger to dogs and cats, if they dig in an area where the fertilizers were recently applied. As you’d imagine, you have to keep kids and pets out of the garden after putting them down.

Organic fertilizers are much less likely to cause injuries or poisoning. Obviously, you’ll want to use some good old-fashioned common sense when handling things like manure or fish gut concentrate (fish emulsion!). But otherwise, they’re much safer than the conventional stuff.

How to Use Organic Fertilizers: The Basics

Like all fertilizers, organic fertilizer products have the NPK number on the packaging. This number tells you how much nitrogen (N), phosphorous (P), and potassium (K) they offer. Compost and manure-based products may not have the NPK label, since the nutrient contents can vary so much between batches.

How do you tell whether a fertilizer product is organic? Usually, it’ll be pretty clear by the wording on the package. To be sure, look for the OMRI-certified label when shopping for fertilizers, which means the product is approved for certified organic growing.

Balanced Fertilizers

You can find balanced organic fertilizer options, which contain a blend of different ingredients to supply all the essential nutrients. These usually have an NPK of around 5-5-5, give or take a little.

Balanced fertilizer blends are simplest to use, but they tend to be a little pricey and hard to find in bulk. They’re often not the most practical for folks with larger gardens. Also, when you blindly apply a broad array of nutrients, you might create a nutrient imbalance over time, depending on what’s already in your soil. 

If you’re a newer gardener working with newer soil, a balanced fertilizer blend will serve just fine and shouldn’t cause any issues. It’s a good way to start fertilizing organically without getting unnecessarily complicated. For balanced blends, we’ve had good results with Espoma’s organic blends such as Tomato Tone (good for any veggie plant!) and Garden Tone.

Making Custom Fertilizer Blends

Once you’ve been growing for a few years (and maybe expanding your garden some!) it’s helpful to get a little more insight into your fertilizing approach. For more targeted feeding, you can get a soil test done to see which essential nutrients are plentiful in your soil and which are lacking. That way, you’re not paying for things you don’t need or unknowingly causing imbalances. The base ingredients you’ll see in balanced fertilizers are often cheaper and available in bulk, if you buy them separately.

A soil test we did for our garden showed we have a reasonable amount of potassium and A TON of phosphorous (bordering on too much) already in the soil. Knowing that, we focus on supplying nitrogen in our fertilizing plan, plus a little potassium for fruiting crops that use a lot of it. That saves us money and will prevent an eventual phosphorous imbalance.

Pro Tip: Don’t google “soil test” and buy one of the first products that pops up. Lots of online soil test kits are overpriced and unnecessarily fancy. Instead, google where your nearest agricultural extension office is. They’ll get you a basic pH and nutrient analysis for much cheaper, and that’s all you need. In our county, they only charge $12 (vs $70 to $100+ for the gimmicky mail-order tests).

Planning Ahead: When and How to Apply Organic Fertilizers

With a few exceptions, most organic fertilizers are granular, raw materials that aren’t water-soluble. You’ll add them directly to the soil based on the application rate you’ll find on the package label.

Unlike conventional fertilizers, dry organic fertilizers take several weeks to a month (or longer, depending on the material) to break down and start feeding your plants. That means you’ll need to plan ahead so the nutrients are available when your plants need them.

I usually apply my dry fertilizers at planting time, whether I’m transplanting seedlings or sowing seeds. That way, they’ll start feeding right around the time the plants hit their first growth spurt and/or begin setting fruit. For heavy-feeding plants, I sometimes do another application midway through the season.

Side Dressing vs. Broad Application

Side dressing is the most conservative and cost-effective way to apply a dry organic fertilizer. That means only spreading it around the base of the plant, right where the roots will have access to the nutrients. You can apply it in a circle around individual plants, or, if you’re planting rows, a line on either side of each row.

When side-dressing with dry fertilizers, keep them at least 3 inches away from the stem, since the stronger types can burn sensitive plan tissue while fresh. You can gently scratch the fertilizer into the soil, being careful not to disturb the plants’ roots, but I usually don’t bother. Rain and watering will take them under the surface, and my mulch layer keeps them from washing away in the meantime.   

Some folks like to apply fertilizer to the entire bed or garden space, instead of side dressing. This method uses more product and increases the potential for waste, but it has its benefits.

First off, it makes it easier to apply the fertilizer a few weeks ahead of planting, if you want the nutrients to be available as soon as your transplants go in. Broader applications can work especially well if you know your soil is really low in essential nutrients. It’s also a good strategy for densely sown crops such as baby greens, which are harder to side dress once they start filling out.

How Much Should You Use?

The amount of fertilizer needed varies a whole lot depending on what you’re using and the plants you’re feeding. Fertilizer products usually have application rates on the package, which is a good place to start. However, you might want to do a little extra research when you’re working with a fertilizer you haven’t used before. With a quick Google search, you can find a lot of resources on using specific fertilizers for specific crops.

Some Good Organic Fertilizers

Depending on what nutrients you need, there are quite a few organic options to supply the essentials. These are some of the most widely available:

For Nitrogen

• Blood meal (12-0-0): Usually sourced from the cattle-processing industry, blood meal is a faster-acting nitrogen source that can start feeding within a couple weeks. It’s strong enough to burn plants, if you use too much at once.
• Feather meal (13-0-0): A slower-release high nitrogen fertilizer that comes from poultry processing.
• Cottonseed meal (5-2-1): A plant based slow-release nitrogen source that also supplies a small amount of phosphorous and potassium.
• Alfalfa meal (3-1-2): Also plant based, alfalfa meal has a lower NPK that makes it good to use in combination with other fertilizers. It’s also rich in trace minerals.   

For Phosphorous

• Bone meal (3-15-0): made from dried and crushed bone from meat processing waste, bone meal is one of the best organic sources of phosphorous. It also supplies a good amount of calcium.
• Fish bone meal (4-16-0): a byproduct of commercial fish processing, fish bone meal is a bit higher in both nitrogen and phosphorous than other bone meals.
• Rock phosphate (NPK varies depending on the source): a mineral-based organic phosphorous fertilizer that supplies slow-release phosphorous, calcium, and other trace minerals.

For Potassium

• Langbeinite (0-0-22): A mineral-based potassium source that’s also rich in sulfur and magnesium, both important micronutrients. Can burn plants if over-used.
• Sulfate of Potash (0-0-50): Another mineral-based fertilizer that provides a big boost of potassium, plus some sulfur. SOP can be either slow-release of water-soluble. Some SOP products aren’t considered organic due to processing methods, so check for the OMRI label.
• Kelp Meal (1-0-2): Made from dried seaweed, kelp meal supplies a small boost of potassium, along with a bunch of other trace minerals and micronutrients. It’s also a good soil conditioner.

Water Soluble Organic Fertilizers

If you need a quick solution to an obvious nutrient deficiency, these water soluble options can come in handy:

• Fish Emulsion (5-1-1): A concentrate made from fish processing waste, fish emulsion is an immediate-release source of nitrogen and smaller amounts of P and K. It’s gentle and non-burning, so it’s great for plants with nitrogen deficiency due to stress or transplant shock.
• Liquid Kelp/Seaweed (0-0-1): Supplies a little potassium and a nice variety of trace minerals. Some gardeners find it can help support stressed seedlings or transplants.
• Sulfate of Potash (0-0-50): Water-soluble SOP provides immediately-available potassium.

In addition to the ones above, you can shop around and find a lot of different balanced water-soluble products for seedlings and for quick nutrient boosts.

Other Natural Sources of Plant Nutrients

You’re not limited to buying fertilizer products from the store shelf when it comes to feeding your garden organically. Here are a few other natural fertilizers to consider:

• Wood Ash: A good source for potassium. Wood ash is highly alkaline and will effectively raise your soil pH, so it’s best to use in moderation and avoid it if your soil’s pH is already on the higher side.
• Aged or Composted Manure: Manure from grazing livestock animals, chickens, and rabbits is rich the full NPK spectrum, as well as calcium, magnesium, and other important minerals and micronutrients.
  
  Fresh manure is too strong for plants and may contain harmful bacteria. To use it safely, it should either be hot composted or just allowed to sit for six months or so. Some folks spread it on the garden fresh in the fall so it can age in place over winter. The exception: rabbit poo is okay to use immediately and doesn’t have to be aged or composted.   
• Compost: Homemade or store bought, compost contains the full array of macro and micronutrients, along with beneficial microbes and fungi and organic material to condition your soil.
  
  Compost releases nutrients slowly, over months as it continues to break down in the garden. It’s generally more helpful for building soil quality than it is for correcting immediate nutrient problems. However, manure-based compost has a higher NPK and will give you faster results as a fertilizer.
• Compost tea: Made by steeping compost in water, then using that water as a soil drench to give plants a gentle nutrient and mineral boost. There’s not an official recipe for compost tea. Some gardeners say to steep for 24 hours, while others let it go for up to a week.
• Comfrey: The comfrey plant is known for accumulating and storing lots of different nutrients from the soil, including nitrogen, phosphorous, potassium, and calcium. You can harvest the leaves and spread them on the garden as “green manure,” or you can steep them to make a liquid fertilizer tea.
  
  Some comfrey varieties are aggressive and invasive, so I’d recommend the Bocking 14 variety (which has sterile seed) if you’re interested in growing comfrey for fertilizer.
• Blackstrap Molasses: Produced during the processing of sugar, molasses is sold as a sweetener, but it makes a good water soluble fertilizer, too. It’s high in potassium, calcium, magnesium, and iron. Molasses also stimulates microbe activity in the soil to make other nutrients more available for plants.
• Epsom Salt: Epsom salt (magnesium sulfate) provides sulfur and corrects magnesium deficiency. Avoid scented Epsom salt products and stick with pure magnesium sulfate. Too much Epsom salt can cause a magnesium imbalance in the soil, so this is one to use sparingly.  

Can You Use Too Much Organic Fertilizer?

While overfertilizing with conventional fertilizers is a lot more likely to cause trouble, overdoing it with the organic stuff can lead to some issues, too.

First of all, make sure you’re following best practices for the type of crop you’re feeding. Loading a root crop (carrots, beets, sweet potatoes) down with a nitrogen-rich fertilizer like composted manure or blood meal can result in small or no roots.

Also, heavy use of certain organic fertilizers can cause an imbalance in soil nutrients over time. Phosphorous buildup in the soil from regular applications of phosphorous-rich manure is a common problem on commercial organic farms. This can happen in home gardens, too, and phosphorous overload can cause significant nutrient deficiencies in your crops.

Phosphorous toxicity in the soil is a whole lot easier to prevent than it is to fix once it happens. If you use a lot of composted manure or other fertilizer with a high concentration of phosphorous, it’s a good idea to get a soil test every few years and keep an eye on the levels.

Do Organic Fertilizers Impact the Environment?

Overuse of conventional fertilizers has a much higher damage potential, but organic options aren’t entirely without impacts.

In the more direct sense, nitrogen from heavy use of manure can still end up in waterways and upset the balance of things. Another thing to consider is the source of organic fertilizer products. For example, manure-based fertilizers, bone meal, blood meal, and feather meal are usually byproducts of the meat industry. We know there are some ethical and environmental concerns tied to the mass production of meat.

Regardless of what kind of fertilizer you’re using, produce grown in a backyard garden comes with a much smaller footprint than that grown on commercial farms. You sort of have to strike a balance between reducing that footprint and doing what’s necessary to get a usable harvest.

Thankfully, there are a few strategies the environmentally conscious gardener can use to grow more sustainably. Things like no-till gardening methods, trench composting, and planting cover crops are some great ways to build more nutrient-rich and resilient soil that needs less fertilizer inputs over time.