How to Use Fertilizer in Your Garden
Different types of garden fertilizer
Sprinkle, spray, dig in to the soil — you’ve probably caught on that there’s more than one way to feed your plants. What’s that about? Plants take up nutrients a couple of ways. Most do it through the root system, so that’s why it’s pretty common to scratch dry products, such as compost and dry, granulated fertilizers, into the soil around the base of the plant. When moisture is added it breaks the particles down so the plant can absorb the nutrients. But some fertilizers can be absorbed through the leaves, especially water-soluble types.
So whether your plant needs granulated fertilizer, water-soluble fertlizer or compost, each type of feeding has options when it comes to how it’s applied. Explore the pros and cons of three types of fertilizers here. Then find the best way to apply fertilizer to your garden.
You Might Also Like:
5 DIY Fungus-fighting recipes for your garden
How to read a fertilizer label
Six organic products to use in your garden
Deter deer in your garden with these deer-control products
Granulated fertilizer
What’s good about it?
Granulated fertilizer is easy to broadcast on the soil.
Some kinds release quickly if your plants need a fast fix; others are slow-release (may be called “timed-release” on the package) for a gentle, long-term feeding.
It won’t need to be applied as often as water-soluble.
What are the drawbacks?
It can “burn” leaves and stems if applied too heavily.
A granulated fertilizer always needs moisture to break it down before plants can use the nutrients.
It may damage roots if it’s left in the soil dry.
Tips for applying granulated fertilizer
In flower beds and borders, broadcast granulated fertilizer by hand and then scratch it into the soil.
Use a mechanical spreader in open areas like lawns.
Always wash fertilizer granules off of foliage.
Activate the granulated fertilizer by watering it in right after applying.
Liquid or water-soluble fertilizer
What’s good about it?
Liquid or water-soluble fertilizer can be diluted to adjust the strength as you mix it.
Great for fast-growing plants because it’s absorbed quickly and rarely “burns” plant tissues.
What are the drawbacks?
Water-soluble fertilizer flushes through the soil quickly, so it needs to be reapplied often.
Tips for applying liquid or water-soluble fertilizers
You can use a hose-end sprayer for large areas.
A watering can is ideal for containers or small areas
Compost or rotted manure as fertilizer
What’s good about it?
Compost or rotted manure can be applied to everything at any time of year.
Both give a gentle, steady feeding that won’t burn your plants.
Both add humus to improve the texture of the soil.
What are the drawbacks?
Hauling wheelbarrows or buckets full of compost can be exhausting.
It’s hard to produce enough to do a large garden so you may need to purchase larger quantities.
Tips for applying compost or rotted manure
Be generous but don’t cover the crowns or they’ll rot.
These both break down over time, so as it decomposes, apply another layer every couple of years.
Work an extra scoop of it into the soil as you plant.
How to Fertilize and Feed Your Plants
You know your houseplants need sunlight and water, but what about fertilizer? Fertilizing houseplants during the growing season can provide them with essential nutrients they need to thrive: nitrogen (N), phosphorus (P), and potassium (K).
Fertilizing your houseplants can seem daunting, but similar to learning how to repot a plant, once you have the basics of fertilizing down, you’ll wonder how your plants ever got along without it. Below we dive into what fertilizer is (hint: fertilizer is not plant food), the different types of fertilizer to choose from, and how & when to fertilize houseplants.
What is fertilizer?
First and foremost, fertilizer is not food for plants. Plants make their food using sunlight in a process called photosynthesis. Fertilizer is more like a multi-vitamin that encourages new, healthy growth. It can also be used to replace essential nutrients our plants' potting mix loses as plants grow over time. Fertilizers can contain quite a few nutrients, but the core nutrients, or macronutrients, are nitrogen (N), phosphorus (P), and potassium (K), which we will talk more about later.
When should I fertilize my houseplants?
Like too much light or too much water—too much fertilizer can damage your plants. We recommend fertilizing houseplants sparingly during the growing season: early spring to later summer. During this time, when plants are actively growing, is when they will benefit from fresh nutrients the most. Generally, you can fertilize your plants on a bi-weekly (every other week) or a monthly basis depending on the fertilizer you’re using. Make sure to read the label provided, as the recommendations on dilution and timeline can vary by brand.
Recently potted or repotted plants will not benefit from fertilizer. Their fresh potting mix is packed with nutrients they have yet to use! To avoid potentially damaging recently repotted plants, wait 2–3 months after freshly repotting before fertilizing actively growing plants during the growing season. If you’ve repotted during the fall and winter months—you can forgo fertilizer until the next growing season.
Note: Fertilizer isn’t necessary for plants in low-light environments because their metabolic activity is slower. They are not using nutrients as much as those in brighter light.
What do the numbers on fertilizer mean?
There are about 17 essential plant nutrients, but 3 of them are prominently displayed on the front of most fertilizers. The three numbers you see are the N-P-K ratio: N for nitrogen, P for phosphorus, and K for potassium. They are the primary macronutrients your plant needs.
An N-P-K ratio on a fertilizer label may look something like 10-5-8. Fertilizers with higher ratios are more concentrated than fertilizers with lower ratios. Keep in mind if a fertilizer has higher numbers, it does not necessarily mean it is a better fertilizer than one with lower numbers—it is simply more concentrated and will require more dilution with water before using.
Your fertilizer may also have micronutrients, making it a complete fertilizer. These can include iron, manganese, zinc, copper, boron, molybdenum, chlorine, etc. Each micronutrient serves a role in plant enzymatic, cellular, and developmental processes—but is not needed in large amounts like the NPK macronutrients. The micronutrients in your fertilizer will most likely be mentioned on the back of the container.
You can use any all-balanced fertilizers (example: 5-5-5) for your houseplants, or you can choose one with a ratio that corresponds to what you are trying to facilitate. For example, a fertilizer with a higher nitrogen ratio is best to increase leaf production, while a higher phosphorous ratio helps to promote fruiting and flowering.
Is solid or liquid fertilizer better?
Fertilizers come in different forms. Choosing what form of fertilizer to use is more of a preference. There are pros and cons to each, and they both supply the essential nutrients plants need.
Liquid fertilizers and powder fertilizers are the most common for indoor plants. Depending on how concentrated they are, i.e., how high their N-P-K ratio is, they can also be the most cost-effective. Liquid and powder fertilizers are also easy to use and dilute with water. Many powder fertilizers can also be added to the potting mix directly.
Solid fertilizers, also called dry or granular fertilizers, are arguably less common for houseplants. They aren’t as easy to dilute, and—because some granular fertilizers are time-release (fertilizer pellets)—you can run the risk of over-fertilization or fertilization when the plant is dormant or slow-growing due to low light.
Is chemical or organic fertilizer better?
Choosing between organic and chemical fertilizers, also called synthetic fertilizers, is also a preference. Synthetic fertilizers tend to be more concentrated and formulated with a near-perfect amount of each macro and micro nutrient. They can be more cost-effective, especially if you purchase them in liquid form to dilute. You can use less and get the same amount of nutrients.
Organic fertilizers are made from all-natural ingredients, like recycled food waste, so they tend to be less concentrated. But mild is a pro, not a con, for houseplant fertilizer. Organic fertilizer can also be a little more costly than other types, but it’s a safe, chemical-free alternative. If you share your space with pets, going with an organic fertilizer might be best.
Organic and chemical fertilizers do the same thing in different ways: delivering nitrates, potassium ions, and phosphates to plants. It’s a balance of personal preference—both yours and your plants’.
6 Quick Tips for Fertilizing Houseplants
Tip 1: Spring is the best time to start fertilizing plants because that’s when they are starting to actively grow. Plants that grow faster should be fertilized more often than plants that grow slowly, like a cactus, or are dormant (i.e., most plants in winter.)
Tip 2: Dilute your fertilizer. It’s best to under-fertilize than over-fertilize. If there is a nutrient deficiency in the potting mix and you have not fertilized in a year or so, you can increase the potency by adding less water when you’re diluting the fertilizer.
Tip 3: Plants that give us fruits or flowers will require more fertilizer in their lifetimes. When we pick off fruits or flowers, we are taking away those nutrients and should restore them.
Tip 4: Know your N-P-K values. That’s the ratio of macronutrients your plant needs and what should be in your fertilizer. It looks something like 10-8-10. If you don’t see this on the package, find another fertilizer.
Tip 5: Micronutrients are just as important as macronutrients, plants just need less of them. Most fertilizers include micronutrients—they’re just not prominently displayed on the front of the fertilizer container.
Tip 6: Organic or chemical fertilizer? It’s your call.
Timing is everything with fertilizer
By Heather Kirk-Ballard
LSU AgCenter Horticulturist
Spring is here and the plants are booming. Plants perform best when they are getting the optimum amount of sunlight, appropriate amounts of water and plenty of essential nutrients for good growth and production of flowers and fruit. Optimize plant growth by knowing how and when to fertilize.
Fertilizers provide the nutrients needed by plants to grow, form flowers and healthy foliage, produce more fruit, establish a strong root system and fight diseases and insect pressures. Plants benefit from fertilizer applications most when they are in their peak growth, and spring is one of those times!
The best time to fertilize is when many plants come out of dormancy in the springtime. In spring, deciduous plants leaf out, flowering plant buds begin to burst, stems and branches elongate and new roots are formed. Nutrients will aid in all of this growth, so the rule of thumb is to make an annual application of fertilizer in the early spring.
There are several ways to fertilize plants, including slow-release granular fertilizers, liquid feed applied to soil as a drench, foliar sprays and fertilizer stakes. In addition, using natural fertilizers such as compost can add nutrients to your soil.
Compost is decayed organic material from other plant materials and animal waste from livestock that has a diet mostly made up from plants. Those include chickens, cows and horses. Composts can be found already bagged at many retail garden centers or available in bulk delivery form from local sources.
Compost also can be made from waste such as grass clippings and fallen leaves in your yard, in addition to kitchen scraps such as coffee grounds, eggshells and fruit and vegetable peelings. Worm castings and mushroom composts are two additional composts that add nutrients to your soil.
Plants can have individual needs when it comes to fertilizers. Acid-loving plants such as azaleas, blueberries, camellias, hydrangeas and rhododendrons prefer more of an acidic soil pH to take up optimal nutrients. Flowering plants need more phosphorus to help stimulate stronger bud, fruit and flower development.
Vegetable plants benefit and require more frequent fertilizer applications throughout the season because they are producing and that makes them heavy feeders. Slow-release fertilizers can be incorporated at planting time for extended nutrient release. Side dress with calcium nitrate at the first and third bloom set. Additionally, some growers utilize liquid fertilizers every other week.
Nitrogen is very important for all plants but especially important for lawns and turfgrasses. Woody plants such as shrubs and trees can benefit from an application of three pounds of nitrogen per thousand square feet and perennials benefit from one pound of nitrogen per 1000 square feet in the spring.
Indoor potted plants may be fertilized with a liquid plant food every month for most varieties. Do this once each season in spring, summer and fall, but skip winter for plants that go into dormancy. No matter the plants you are trying to feed, scheduling the correct timing is important.
Applying fertilizer in the wrong season can cause increased tender new growth that can be damaged, especially if applied in cold weather in late fall or in winter. So it is best to stop fertilizing during dormant seasons. Additionally, in zones that can be in danger of a late freeze, it’s best to wait until mid-spring. Everyone could benefit from putting fertilizer application schedules in their calendars.
Here are some general rules to follow when fertilizing:
Avoid fertilizing new plants until they are fully established, because it can cause an increase in tender new growth that can make the plant weak and leggy.
Always follow the manufacturers recommended rates and application methods.
Fertilize outdoor plants in the coolest part of the day, such as early morning or late evening, especially in hot summer weather.
Always water in fertilizers well to distribute nutrients throughout the soil profile and to prevent burning.
Lastly, avoid excessive fertilizing and perform soil tests annually to see what nutrients your plants need.
With fertilizer prices doubling as they have, waste not!
