Buying guide for best garden fertilizers
Healthy soil isn’t always a guarantee. The earth in your area may not provide the necessary nutrients for a lush garden. The potting soil mix you’ve added to your garden beds may be deficient in some nutrients. Over time, plants also leach nutrients from the soil.
Garden fertilizer is a vital gardening tool and a simple way to help vegetables, flowers, and other plants flourish in soil where nutrients are scarce or present in the wrong quantities.
The BestReviews team wants to help you grow flowers, vegetables, and herbs with ease. Our shopping guide covers the various types of garden fertilizers, including information on macronutrient ratios and what type of fertilizer may be best for your gardening needs. When you’re ready to make a purchase, our product list will help guide you toward the best products available. Happy gardening!
Types of garden fertilizers
Here are the three main forms of garden fertilizer, how they’re applied, and the advantages of each.
Granular
Fertilizers in granular form are dry. You can apply granular fertilizers with a spreader or use the built-in shaker top on some canisters. You can easily see how much you’re applying and where, so you can control the application. Many dry formulas are water soluble and can be diluted using a watering can, making it easy to fertilizer and water your garden at once. There are two types of granular fertilizers.
Slow-release fertilizer provides the steady release of nutrients over an extended period of time, so frequent application isn’t necessary.
Quick-release fertilizer delivers nitrogen to plants almost immediately, but it requires frequent application. This fertilizer isn’t intended for general plant maintenance because it can harm plants if poorly applied. Use it to address specific deficiency issues.
Liquid
Most liquid fertilizers need to be diluted with water and are applied using a canister and hose. Gardeners can also manually mix liquid formulas with water in a watering can. Liquid fertilizer is very easy to apply and is quickly absorbed through leaves and roots, making the nutrients readily available to plants. This type of fertilizer requires frequent application. The downside is that it easily washes away in the rain and can contaminate nearby water sources.
Spikes
Compressed fertilizer in the shape of spikes that you stick in the ground is convenient and easy to use. This form of fertilizer slowly releases nutrients over time. The spikes don’t require dilution and don’t need to be precisely measured, so this is an excellent choice for the novice gardener or those short on time.
Testing garden fertilizers
We spent 68 hours researching 24 garden fertilizers before picking our top 5. We then purchased our favorite model and tested it in our lab.
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Garden fertilizer considerations
When shopping for garden fertilizer, keep these factors in mind.
Soil composition
- Soil nutrients: Before you start pouring fertilizer all over your garden, have the soil tested. Adding fertilizer without knowing your soil’s composition might create a nutrient imbalance that can prevent optimal plant growth. For instance, too much nitrogen will make your tomatoes very leafy and green, but the plants won’t produce as much fruit. If you’re growing legumes, you don’t even need a fertilizer with nitrogen since these plants fix nitrogen in the soil.
- Soil pH: The pH of your soil can also affect your garden. The wrong pH can prevent plants from absorbing nutrients.
NPK
The number on that fertilizer bag you’re eyeing? It’s the ratio of macronutrients – nitrogen (N), phosphorus (P), and potassium (K) – in the mix. For example, a bag marked “4-4-4” means that it contains a 1:1:1 ratio of these elements: 4% nitrogen, 4% phosphorus, and 4% potassium, and the rest is filler. Some mixes include trace amounts of micronutrients like calcium. Most other nutrients are needed in smaller amounts or are readily available in the soil. Each macronutrient has a particular function.
- Nitrogen: Encourages lush, leafy growth
- Phosphorus: Promotes root growth, fruiting, and flowering
- Potassium: Strengthens plants against disease, drought; encourages root growth
Typical NPK ratios and their benefits include the following:
1-1-1: All-purpose fertilizer
1-2-1: Root systems
1-2-2: Fruit setting and flowering
3-1-1: Leafy growth
The above ratios are guidelines. The fertilizer that will help your plants depends significantly on the nutrient composition of your soil. Adding a fertilizer intended to encourage green growth won’t do you any good if your soil is already rich in nitrogen. Only a soil test can alert you to deficiencies that need to be addressed.
Fertilizer quantity
Even if you’ve discovered an imbalance in your soil through testing, don’t overdo it! Too much fertilizer can burn and even kill your plants. Carefully read the fertilizer package instructions and dilute accordingly if needed.
Synthetic vs. organic fertilizers
Fertilizers are available in both synthetic and organic formulas.
- Synthetic fertilizers: These products release nutrients more quickly and are available in both granular and liquid form. They’re also typically cheaper than organic formulas.
- Organic fertilizers: Organic formulas release nutrients more slowly and are usually not very concentrated, making it difficult to harm or kill plants by using too much fertilizer. For alternatives to synthetic fertilizers, consider bone meal for calcium and phosphorous and blood meal, which is high in phosphorus. Other organic fertilizer options include compost, manure, kelp, and fish emulsion.
Season
Timing fertilizer application just right is the key to developing a lush, healthy garden. Applying fertilizer at the wrong time is a waste of time and money because the nutrients may soon be blown or washed away. The following are some fertilizer application guidelines.
- Spring: Perennials and veggies
- Spring and fall: Trees and shrubs
- Late fall: Bulbs
We look at granular fertilizers that come in both slow-release and quick-release formulas, factoring in the positive and negative aspects of each type.
There are three main types of garden fertilizers: liquid, granular, and spiked. We research all three varieties, evaluating the pros and cons of each to help our readers decide which one would best suit their needs.
Liquid garden fertilizer is easy to use, but it washes away quickly and must be reapplied often. We research the effectiveness of liquid garden fertilizers when shortlisting products.
Nitrogen, phosphorus, and potassium (NPK) are macronutrients in garden fertilizers, and they are measured in ratios. We look at the ratios offered in various products, thinking about which plant systems and growth needs they’re suited for.
Some people want fertilizer that is quick and easy to use. For this reason, we pay special attention to spike fertilizers, which are appreciated by many gardeners.
We look at many liquid garden fertilizers that must be mixed with water, taking note of how easy this task is and how effective the product is.
Some garden fertilizer is pricey, yet it doesn’t seem to work as well for certain plants. We research this aspect of each product before deciding whether to recommend it.
We look at synthetic and organic garden fertilizers, assessing the pros and cons of both varieties.
We appreciate granular fertilizers that come with a shaker top lid. Application of this type of garden fertilizer is quite user-friendly.
When examining granular fertilizer, we want to know if it’s water-soluble, a feature that comes in handy for watering and fertilizing plants at the same time.
Tips
Have your soil tested before applying fertilizer. That way you’ll know what nutrients are already present or lacking in the soil. Timing the application of fertilizer correctly won’t matter if you’re feeding your plants nutrients they already have in abundance.
Bone meal and blood meal are meat industry by-products. Vegan and vegetarian gardeners should read fertilizer contents carefully.
Watch the concentration of nutrients. Keep in mind that a fertilizer with a high concentration of one nutrient isn’t necessarily better than one with a lower concentration. A high concentration in a quick-release formula may cause root burn or create a nutrient imbalance in your soil. A lower concentration of a slow-release formula, on the other hand, is a better option.
- Avoid fertilizing in rainy or windy conditions, depending on the formula. Don’t fertilize in your area’s rainy season or if you know a heavy storm is coming. The fertilizers will be washed away. Dry fertilizer applied in windy conditions is likely to blow away.
Garden fertilizer prices
Fertilizers range in price from under $10 to $80. Smaller bags for container plants are the least expensive and won’t set you back more than $20. On average, expect to pay between $0.10 to $0.50 per square foot to fertilize a garden or lawn. If you plan on hiring someone to do the work, you’ll need to factor in the extra cost. Tools such as fertilizer spreaders are another expense to take into consideration.
Unsurprisingly, larger bags and bins of fertilizer cost more. Specialty fertilizers with added micronutrients may be more expensive, too. Organic fertilizers also usually cost more than synthetic options. When fertilizing large swaths of land, buying in bulk is the most economical option.
FAQ
Q. Are fertilizer and compost the same thing?
A. Kind of. Compost amends the soil, while fertilizer delivers nutrients directly to plants and not the soil. Fertilizers still end up in the soil, though, so it’s important to be careful not to add them haphazardly. Unlike most fertilizers, compost contains many trace nutrients, such as boron. Compost is often classified as an organic fertilizer, but compost doesn’t have the same concentrated amounts of NPK as synthetic fertilizer.
Q. Is there a way to know if my soil is nutrient deficient without a soil test?
A. Deficiencies can be hard to spot, and the only way to know for sure is to get your soil tested. Phosphorous deficiency usually results in stunted plants, but a number of other factors can contribute to weak growth. Yellowing leaves can be a sign of potassium deficiency, but, again, it’s tough to tell for sure that your soil is lacking this specific nutrient.
Q. I live near a water source. Can I use fertilizer in my garden?
A. Opt for organic fertilizer to prevent contamination of ponds, lakes, rivers, and wells. Organic formulas typically aren’t as concentrated as synthetic fertilizers and are designed to release slowly. Unless you pour organic fertilizer everywhere without concern, it shouldn’t pose a threat to surrounding ecosystems.
