Compost Vs. Fertilizer: Differences and Garden Uses
Compost and fertilizer benefit the garden, though they have different applications! Use one, the other, or both—which to apply depends on your garden’s soil and which crops you’re growing. Learn the differences and uses of fertilizers and compost alongside seasoned grower Jerad Bryant.
Contents
Amendments turn poor, nutrient-deficient soils into rich, fertile, and absorbent ones. They’re a crucial part of a healthy garden; they replace the nutrients lost from plant growth. After a long growing season, plants may have used most of the nutrients, leaving nutrient-poor, dusty soils.
Compost is a soil-booster and nutrient-giver, whereas fertilizers are mainly nutrient-giving. They lack the beneficial effects of compost, like better drainage, more worms, and a higher microbial presence. Though composts are doubly beneficial, they often lack the high levels of nutrients that fertilizers deliver.
So, which is best for you and your garden? Here’s a detailed analysis of compost vs. fertilizer, and which settings call for which material.
Espoma Bio-tone Starter Plus Organic Plant Food (4 lbs.)
Espoma Bio-tone Starter Plus Organic Plant Food (4 lbs.)
Compost Vs. Fertilizer
There are a few key differences between composts and fertilizers. Look at this chart for a quick breakdown:
| Compost | Fertilizer |
| High in organic matter | High levels of specific nutrients |
| Increases soil drainage and fertility | Best for high feeders, like vegetables |
| Well-balanced | Synthetic and organic types |
| Controls weeds | Pellets, granules, dusts, and liquid forms |
Compost feeds the soil food web, whereas fertilizers mainly feed plants. Because of their inherent natures, they target different problems and situations. Use compost for overall garden health and fertilizer to feed hungry plants.
What is Compost?
Compost is like the duff you find on forest floors. It consists of broken-down and decomposed plant clippings, wood products, and kitchen scraps. With regular turning, or rotating of the materials, and occasional watering, you can convert waste into nutrient-rich compost!
How to Make It
It’s not hard to make, and anyone can do it! You simply need “greens” and “browns.” Greens are nitrogen-rich waste materials, while browns are carbon-rich ones. For every shovelful of greens, add two to three shovelfuls of browns.
Common greens are kitchen scraps, grass clippings, and animal manure. Browns include things like fallen leaves, paper, cardboard, and straw. Water the pile well, then use a pitchfork every day to rotate the parts of the pile.
After a few weeks to a few months, your refuse pile will start looking less like trash and more like the black gold for the garden, compost! Its final nutrient content will depend on the materials you put in the pile.
Benefits
Compost helps way more living things than plants—it impacts worms, butterfly and moth larvae, fungi, bacteria, archaea, beetles, and ground-dwelling bees, to name a few! It also contains humus, a valuable soil particle that’s both porous and absorbent.
The more soil critters you add, the better your soil will be for veggies and fruits. Worms create channels in the dirt that help plants breathe, and they recycle decaying organic matter into castings, which are nutrient-rich waste particles.
Adding this mulch will also protect plant roots from droughts and soggy conditions. When there’s lots of rain, the porous humus absorbs the excess moisture and prevents roots from sitting in standing water. During hot, dry seasons, the top layer prevents moisture from evaporating and holds it for roots to access.
When to Use
I like to add two helpings of compost a year, though three or four is also acceptable. An easy schedule to follow is once in early spring and once in early autumn. It’ll supply fresh seedlings with a steady source of nutrients and protect them from pests in the spring. In the fall, mulch keeps plant roots warm despite frosty weather.
When frosty weather arrives, it’s too late to add this amendment; you’ll have to wait until spring. Midsummer is also a good time to apply it, as heat-loving crops will be hungry for nutrients and organic matter.
What is Fertilizer?
Like compost, fertilizers can also consist of organic matter, though synthetic kinds are manufactured from a variety of sources. Regardless of the type, fertilizers are concentrated applications of nutrients.
Some products contain specific nutrients, while others have a balanced blend of many different types. Which fertilizer to use depends on your garden soil’s current nutrient levels. If you’re unsure of its content, consider using a soil testing kit to know for sure.
Benefits
Fertilizer is especially beneficial for nutrient-hungry plants. Tomatoes, eggplants, cabbage, and peppers are especially hungry, though many vegetables benefit from regular applications.
Crops in containers, planters, and raised beds benefit from monthly or bimonthly fertilizer applications during the growing season. They need a steady supply to produce fruits, veggies, and leafy greens.
I recommend using organic fertilizers rather than synthetic ones, especially for food crops. Organic fertilizers take longer to hit the plant roots than synthetic types, though they’re less harsh on the soil food web. Salt-based fertilizers kill microbes and harm soil-dwelling critters, especially in large doses.
When to Use
Use fertilizers as a way to feed your crops during the growing season. Though they don’t boost the soil food web as much as compost, they do have lasting effects on underground critters. Organic fertilizers are especially beneficial—they feed microbes that convert the nutrients into a form that plants can use.
How often to add fertilizer depends on your crops. Consult guides for each species, as each one will have different preferences. Herbs and leafy greens manage well with few applications, while quick-growing crops like corn, tomatoes, and squash require consistent nutrients.
Apply fertilizers according to their instructions at any time during the growing season. Avoid adding them after your first average frost date, as garden plants will be dead or dormant after recurring frosts and won’t need the resources.
Can You Use Both Together?
Yes, you absolutely can use compost and fertilizer together! Combining them is a great way to feed your plants and the soil microbiome. The microbes in the compost will help break down the nutrients in the fertilizer, creating a win-win scenario for your garden.
When using both, consider the nutrient levels in your compost. You don’t want to overfertilize, as it can cause significant issues for your budding crops. Consider sampling your pile with a soil testing kit to determine how much nitrogen, phosphorus, and potassium it has.
After testing, add fertilizers to the pile to bring the nutrient levels up to par with your plants’ needs. Regardless of which amendments you’re adding, always water them well to help them mix with the dirt.
Common Problems
Some common issues may occur with improper doses of fertilizers and compost. Adding too much, not enough, or the wrong kinds can have significant impacts on the soil microbiome. Always follow dosage and application rates on products’ labels, and consider testing your soil first before amending it.
Ignoring Soil Testing
Soil testing helps prevent both over- and underfertilizing. Without it, you’ll be making a blind guess as to how much nitrogen, phosphorus, and potassium there already is. Use a simple kit from online, or consult local university extension offices.
University extension services, such as those from the Master Gardener program, run soil testing days where you can submit multiple samples. This is a cheap and effective way to test the ground without burning a hole in your wallet!
Overfertilizing
Too much fertilizer can be deadly for plants, no matter if it’s synthetic or organic. Ignoring dosage instructions and your soil’s current nutrient levels can lead to overfertilizing.
Watch for signs of excess nitrogen, like dark leaves, yellow margins, and necrotic spots. If you suspect you’ve overfertilized, you may leach the stuff out with a steady stream of water. Set your hose to trickle on low for an hour wherever you added too much fertilizer.
Not Enough Fertilizer
Like overfertilizing, underfertilizing can also negatively impact plants. Watch for signs of nutrient deficiency, like yellow leaves on lower stems, weak growth, and chlorosis. You may see yellowing between leaf veins, in the margins, or on entire leaves on the lower portions of the plant.
Underfertilizing is easy to fix! Simply add more fertilizer to meet your crops’ needs. If you added compost and it’s low in nutrients, consider adding some fertilizer alongside it.
Too Thick of a Layer
Thick layers of mulch can suffocate seedlings, shrubs, and annual veggies. Keep the compost layer between two and three inches thick, and avoid having it touch the plant stems.
If the layer is too thick, use a rake or similar tool to distribute it evenly throughout your garden beds. Keep it under three inches for the best results.
Key Takeaways
- Fertilizer and compost are both helpful in home gardens.
- Add fertilizer to feed plants.
- Add compost to feed the soil microbiome and your plants.
- Compost boosts the drainage, porosity, and fertility of existing soils.
- Consider testing your beds to see their nutrient levels so you can properly amend them.
Frequently Asked Questions
Which is better, compost or fertilizer?
Neither is better, they just have different use cases! I am partial to compost, though, and I favor it over fertilizer for its wide range of benefits.
Can you use compost and fertilizer together?
Yes, you can! Avoid adding too much by testing the area first before calculating dosage rates.
Can compost replace fertilizer?
Yes, it can, though it depends on the type of compost and how often you add it. Put nutrient-dense things in your pile like manure, alfalfa meal, and grass clippings to boost its levels.
