Soil Amendments & Fertilizers 101 Guide

Great plants grow best in healthy garden soil. After all, plants need nutrients and trace elements for robust root growth, healthy foliage and abundant flowers.

Are you jumping right into full-scale Backyard Orchard and container culture to feed your family with homegrown fruiting plants?

Just getting started with a tiny Victory Garden or Salsa Garden on your balcony or deck?

Or, are you a first time homeowner with established plantings and a…gulp…lawn?

No matter what kind of gardener you are, you'll love watching your plants grow. And never before have there been so many innovative choices for gardeners.

Technology for plant production has migrated from commercial growing systems into the home marketplace. It’s easy to get your hands on everything from hydroponic systems to LED grow lights.

So, what happens when you are just getting started? It’s pretty easy to feel overwhelmed.

Let us help you get a good basic overview of plants and what they need to thrive. We spoke with our friends at Urban Leaf to ensure that this blog post is an easy read of soil amendments and fertilizers that support plant growth.

You’ll learn:

If you should use fertilizer products at all.
Why and how you should use fertilizers during the growing season.
When you should stop using them.

Feed your plants what they need when they need it!

As you continue in your journey as a gardener, you’ll have more in-depth questions on crops or plant species. Search the #ProPlantTips blog and #ProPlantTips on the product pages for specific advice on your chosen plants.

First, Make Good Plant Decisions for Your Sun Exposure and Soil Type

Every product page on our website has Plant Highlights listed. You’ll learn the optimal growing conditions for your plants, including sun exposure, water, and soil requirements.

Get off to the best start by making the right plant choices for your landscape. A desert plant will likely rot in a damp wetland. An acid-loving plant will suffer in alkaline soil. Sun-lovers won’t bloom in deep shade.

Next, get your soil tested to understand the levels of nutrients already present in your soil. Use a kit you buy online, or ask your state Ag Extension office for more complete testing.

There is no need to amend your soil if you don’t need to. In fact, you can also do more harm than good by “overdoing it” with synthetic soil amendments.

You will definitely want to know your soil pH, which ranges from 1 – 14. Anything below 7 is considered acidic.

Some plants prefer acidic soil. As an example, Blueberries fruit best in acidic soil around 4.5 on the scale. But vegetables need more neutral soil.

States in the north and southeastern United States generally have more acidic soil. Western states usually feature alkaline soil, which is above 7.

Choose plants that work in your area. You can also use raised beds or containers, where you can more easily control the soil conditions.

Sweeten up acidic soil over time with garden lime. Lower pH with Sulphur and pine straw mulch. Test your soil every year or so to avoid overdoing it.

You may also have deficiencies in micronutrients that can be corrected once you know what you are dealing with. It's very important to get your soil tested!

The Basics of How Plants Use Primary Nutrients

Keeping it simple, you’ll see the “NPK” rating listed on packaging of soil fertilizers. Most garden fertilizers contain three major plant nutrients: nitrogen, phosphorus, and potassium (N-P-K). The formulas can also contain small amounts of calcium, magnesium, iron, sulfur and boron.

N= Nitrogen for Leaves

Nitrogen is all about green foliage development. Organic lawn fertilizer will have a larger number listed first. After all, grass fertilizer is designed to develop lush, green foliage growth.

Use care when applying high nitrogen lawn formulas around flowering and fruiting plants. You want to avoid over-feeding nitrogen, or you’ll actually reduce the amount of flowering.

Carefully apply Lawn Weed and Feed according to directions. It’s best to wait for a day that isn’t windy to apply.

See all Nature Hills Lawn Care formulas.

P = Phosphorus for Roots, Flowers and Fruit

Phosphorus helps plants develop both roots and flower buds. This is a critical nutrient to support the production of fruit and seed.

K = Potassium

Potassium supports overall growth by helping move nutrients and water through the plant. You’ll get brighter flowers, better shape and growth habit, and more flavorful fruit with this important nutrient.

Acid-loving plants need specialized formula that maintain proper pH levels.

Rose fertilizer supports the robust flowering of these gorgeous shrubs.

Trees and Shrubs can be fed in early spring and mid-summer.

Houseplants should be fed only once the days get longer in springtime. There is no need to feed them during winter dormancy.

Fruiting plants require specialized formulas. Blueberry fertilizer supports a low pH to encourage fruiting. Use a Citrus fertilizer for best flower and fruit production, especially if you are growing in indoor/outdoor container culture.

Growing organically? Use an organic formula. We feature many great brands on our site.

Balanced fertilizers show the numbers 10-10-10 on the label. These are good, all-purpose, slow-release fertilizers used to support the needs of many types of plants.

When to STOP Using Fertilizers

For landscape plants, it’s usually best to apply formulas in early spring as new growth emerges. Some heavy feeders, like Roses, need another application again in mid-summer.

Don’t apply fertilizers in late summer or fall, especially in zones that have cold winters. You’ll risk exposing a fresh wave of new growth to extreme temperatures.

For Healthy Plants, Boost the Roots When Planting

Healthy, vigorous plants ward off diseases and insect pressure far better than unhealthy ones. Protect your investment in landscape and fruiting plants by focusing on root development.

Healthy soil is filled with a microcosm of millions of naturally occurring helpful bacteria and mycorrhizae fungal organisms. Think of these as probiotics for your plants.

Mycorrhizae fungus is one of the best ways to support your plants over their whole life cycle. It partners with your plant to increase the root’s ability to access water and nutrients.

Adding Nature Hills Root Booster to your planting hole gives you an easy-to-use mycorrhizal inoculant. Your plants will develop a bigger, more efficient root system when you use this product. That translates to a healthier plant.

Even with existing plantings, Nature Hills Root Booster is helpful. Pour the packet around the soil surface, and scratch it in using a garden fork. Water it in well, and you’ll be on your way to seeing a leap in productivity.

Root Booster partners with your plant in a symbiotic beneficial relationship. It will also improve your soil naturally, and help your plants gain access to nutrients and moisture.

Another product that supports healthy root production is Fertilome Root Stimulator & Plant Starter Solution. It is added to water and applied on all newly planted flowers, shrubs, trees and houseplants. It has a 4-10-3 ratio and will jump-start stronger root structure to naturally develop more vigorous growth.

High Density Planting in Small Space Gardens

People are seeking out opportunities to add fruiting plants and vegetables gardens in small spaces. This is where the smart use of fertilizers and technology comes into play.

Since the 1930s, the use of synthetic commercial fertilizers have produced big yields in a small footprint. Universities have a wealth of research on the chemistry requirements of specific agronomic crops.

These days, many homeowners understand that yearly and general overuse of these chemical fertilizers with high percentages of nitrogen have had some adverse effects on groundwater and runoff.

Organic fertilizers, while perhaps a bit less precise, are a readily available and environmentally-friendly resource for homegrown food crops. There are many to choose from, so we’ve prepared a list of some of the most common options.

Get Bigger Yields With Common Organic Fertilizers and Soil Amendments

You can add soil amendments as single ingredients by themselves, but they can often be found in combination as part of a balanced prepared fertilizer formula. These plant “superfoods” are designed to provide a boost in performance.

It is important to choose the right formula for your plant.

They come packaged in a variety of ways, including: foliar sprays, granules, and liquid fertilizers. Spray the leaves with foliar sprays, “top-dress” the soil surface with granular fertilizers, and apply liquid fertilizer after it has been diluted in water.

“Slow release” fertilizer provides nutrients that are available to the plants over a longer period of time. Look at the label to see how long the fertilizer will benefit the plants. Every manufacturer also has different application rates, so following the label directions becomes important.

Don’t waste money with too much product. At the same time, don’t limit your success with not enough product.

Garden newbie? Get ready to be amazed (and maybe a little grossed out) at this list of wild, weird, wonderful, and effective soil amendments.

Alfalfa Meal is a nitrogen fixer and a reliable source of nitrogen. Gardeners use this as a spring-time top-dressing applied on the soil surface of many flowering plants and vegetables. It acts as a soil conditioner to increase both nitrogen and organic matter in the soil.

Bat Guano enriches the soil and can activate compost. Use this on lawns and landscape plants to support foliage growth.

Blood Meal is a great source of naturally occurring nitrogen. Use on plants that have yellow or pale green chlorotic leaves that are struggling to produce enough chlorophyll. It can repel rabbits and deer, as well.

Bone Meal provides phosphorus and encourages root production, blooming and fruiting. This can be used on Roses as a support for up to 4 months.

Cottonseed Meal conditions the soil, while slightly lowering the pH over time. It is great for acid-loving plants like Azaleas, Blueberries and Japanese Maples. As a nutrient-rich organic material, it also supports beneficial bacterial and fungal colonies in the soil.

Compost improves your soil and can feed all your trees, shrubs, perennials, Roses, and veggies. Include a few handfuls in your planting hole, and use annually as a top-dressing.

Cow Manure must be well aged before you apply to landscape plants. Once composted, cow manure helps improve soil conditions and adds healthy organic material.

Earthworm Castings provide plants important beneficial microorganisms and aid in disease resistance. They can be added to the top few inches of backfill soil when planting, used as a mulch, or included in the compost pile.

Fish Emulsion or Fish Bone Meal supports plants as an all-purpose fertilizer. Different formulas can be used as a foliar spray on the leaves, or added to water as a soil drench to feed both plants and helpful microbes.

Kelp Meal increases yields by supporting your plant’s ability to take in nutrients. It can be used on flowers, trees, and vegetables to increase vigor.

Pine Bark mulch naturally lowers pH for Blueberries and other acid-loving plants. Test your soil regularly to understand the acid-base balance of your soil.

Potting Mixes can be considered fertilizers when added in handfuls to backfill soil during planting. Fertilome Ultimate Potting Mix improves performance as a soil amendment. Designed for containers, use Fertilome High Performance Potting Mix to feed plants for 8 months.

Rock Phosphate is a nutrient-rich dry powder that help plants deliver big blooms and abundant fruit set. Roses and vegetables can readily utilize this natural source of phosphorus.

Urea is an enriched source of nitrogen that greens up foliage quickly.

Get the most from your plants with thoughtful use of Root Boosters, soil amendments and fertilizers. The right amount of sun, air and water along with great soil are the keys to successful plant gardening. Enjoy!

Frequently Asked Questions

What is the difference between soil amendments and fertilizers, and when should I use each in my garden?

Soil amendments improve the physical structure and chemistry of your soil, such as adding compost to improve drainage or sulfur to lower pH for acid-loving plants like blueberries, while fertilizers directly supply nutrients like nitrogen, phosphorus, and potassium to feed plant growth. Before using either, get your soil tested through a home kit or your state Agricultural Extension office to understand exactly what your soil needs, since over-amending with synthetic products can do more harm than good. Apply fertilizers during the active growing season when plants can actually use the nutrients, and taper off in late summer to avoid pushing tender new growth that can be damaged by frost. Start with a soil test, match your amendments and fertilizers to what your results show, and always follow product label rates to avoid nutrient imbalances.

How do I add organic matter to soil to improve its structure and fertility?

Adding organic matter like compost, aged manure, or shredded leaves is one of the most effective ways to improve soil structure, drainage, and fertility over time. Work 2 to 4 inches of compost into the top 6 to 12 inches of soil before planting in spring or fall, or apply it as a top dressing around established plants. Get a soil test first to understand what your soil already contains, so you avoid over-amending and creating nutrient imbalances. Start with a quality compost or organic mulch, apply it consistently each season, and let nature do the work of breaking it down into the beneficial humus your plants need.

How do I read a soil test to know which amendments my garden actually needs?

A soil test report will show your pH level on a scale of 1 to 14, with 7 being neutral, along with readings for key nutrients like nitrogen, phosphorus, and potassium. If your pH falls below 6.0 for most general garden plants, you may need to add lime to raise it, while a reading above 7.5 may call for sulfur to lower it. Your report will typically include amendment recommendations with specific application rates, so follow those numbers closely rather than guessing, since over-amending can damage your plants just as much as doing nothing. Start by contacting your state Ag Extension office for a thorough test, then purchase only the amendments your results specifically indicate you need.

When should I amend soil before planting flowers, vegetables, shrubs, or a new lawn?

Amend your soil before planting once you have reviewed your soil test results and confirmed there is an actual deficiency or pH imbalance to correct. Adding amendments without testing first can do more harm than good, throwing off the nutrient balance your plants depend on. For new lawns, flower beds, vegetable gardens, and shrub borders, work amendments into the top 6 to 12 inches of soil in spring or fall before planting. Get your soil tested first through a kit or your local state Ag Extension office, then amend only as directed by the results.

How do I choose the right soil amendment for sandy, clay, or compacted soil?

Choosing the right soil amendment depends on your specific soil problem. Sandy soils drain too quickly and lack nutrients, so work in generous amounts of compost or aged manure, about 3 to 4 inches tilled into the top 12 inches, to improve water and nutrient retention. Clay and compacted soils benefit from the same compost addition, along with coarse horticultural grit or expanded shale to improve drainage and break up density. Start with a soil test through your local state Ag Extension office to confirm your soil's exact needs before amending, then apply corrections in fall or early spring before planting season begins.

Should I mix amendments into the soil or top-dress them onto existing garden beds?

Both methods have their place depending on your situation. When establishing new beds or planting, mix amendments like compost, peat moss, or lime thoroughly into the top 8 to 12 inches of soil so roots have immediate access to improved nutrition and structure. For established plantings where you cannot till without disturbing roots, top-dressing with compost or granular fertilizers and watering them in is the preferred approach, as nutrients will gradually migrate down to the root zone. Test your soil first to determine what your beds actually need, then apply amendments accordingly rather than guessing.

How often should I add compost or other amendments to keep garden beds healthy?

Most garden beds benefit from a 1 to 2 inch layer of compost worked into the top few inches of soil each spring before planting, with a second application as a light top dressing in fall after the growing season ends. Before adding any amendments, get your soil tested through a home kit or your state's Cooperative Extension office so you know exactly what your soil needs rather than guessing. Over-amending, especially with synthetic products, can disrupt soil chemistry and harm your plants just as much as neglecting it. Start with a soil test, amend only what is lacking, and let compost be your consistent annual foundation for healthy, productive beds.

Can I use the same soil amendments for raised beds, containers, and in-ground gardens?

While some amendments like compost and balanced fertilizers work well across all three settings, containers and raised beds typically require more frequent fertilization since nutrients leach out faster with regular watering. In-ground gardens benefit most from slow-release and organic amendments worked into the native soil, while containers need a well-draining potting mix rather than straight garden soil, which can compact and suffocate roots. Get a soil test before amending in-ground beds, and refresh container and raised bed mixes with compost each season to maintain nutrient levels and soil structure.

Why do plants in amended soil still struggle, and what common mistakes should I avoid?

Plants in amended soil often struggle because gardeners skip soil testing and add unnecessary or incorrect amendments, creating nutrient imbalances or pH problems that are worse than the original conditions. Over-fertilizing with synthetic products is one of the most common mistakes, as excess nutrients can burn roots and disrupt the microbial activity that healthy soil depends on. Before adding anything to your soil, order a soil test through your state Agricultural Extension office or purchase a reliable home kit, then amend only what the results show is actually deficient.

How do I build a long-term soil health routine using amendments and fertilizers together?

Start with a soil test every 2 to 3 years to establish a baseline for pH and nutrient levels, then use organic amendments like compost worked into the top 6 to 8 inches each fall to build long-term soil structure and microbial activity. Layer in a balanced slow-release fertilizer at the start of the growing season, typically after your last frost date, and supplement with liquid fertilizers during peak growth phases when plants need a quick nutrient boost. Stop all fertilizing 6 to 8 weeks before your first expected frost to avoid pushing tender new growth that winter will damage. Get your soil tested this season through your state Ag Extension office, then build your amendment and fertilizer plan around what your soil actually needs rather than guessing.

#ProPlantTips Soil Amendments and Fertilizers 101