Imagine somebody coming up to you and saying "Here, take this great vitamin! I guarantee that if you take it on a regular basis, you’ll feel and look great!"
What would your reaction be? More than likely, you’d ask this person some questions. What’s in this vitamin? How does it work? How often and for how long should I take it?
In other words, you probably wouldn’t just take the vitamin and hope for the best.
Yet when it comes to fertilizers, many gardeners take exactly this approach. We sprinkle and spray on a regular basis because the horticulturist at our local garden centre recommended it, or a manufacturer’s commercial tells us that our garden is better off if we use their product. In short, we give our gardens the vitamin no questions asked.
Why do we do this? Well for one thing, gardening is a great hobby because it’s so easy. Whether you have an acre for a backyard or a balcony of containers, a little bit of elbow grease, basic pruning and regular watering are usually all it takes to reap rich rewards.
Fertilizers on the other hand, come across as a topic that’s either too scientific or just plain boring. Many people would rather research varieties of roses or hostas instead of reading a fertilizer package with all its references to "12-8-10", "mineral composition" and "NPK ratios". It can leave you feeling like you’ve got to memorize the periodic table of the elements just to get started.
But take heart, because nothing could be further from the truth. Understanding fertilizers is as simple as understanding some basic principles about how your garden grows — and understanding is the difference between a "good" garden and a "great" one.
Start at the Ground Level
All gardens start with soil, which is simply a collection of organic compounds and minerals that feed your plants. Your soil contains many minerals including calcium, magnesium, sulphur, boron, cobalt, copper, iron, manganese, molybdenum and zinc. It also contains micro-organisms that continually break down organic matter into usable nutrients.
A typical garden produces enough minerals and organic matter on its own, so there is rarely a need to supplement them. But fertilizers can be of tremendous benefit in two key areas: soil composition and plant nourishment.
Fertilizers that affect soil composition are known as "amendments" because they change the structure of soil itself, delivering nutrients more effectively to your garden. Amendments include: peat moss, compost, limestone, grass clippings, gypsum, slugger, and worm castings. For example, compost and peat moss will thicken your sandy soil and keep it from losing too much moisture, or they can help break up soils that are too thick (mainly clay).
Make an overly acidic soil more alkaline by adding limestone. If your garden needs to be more acidic, try using slugger.
The second group of fertilizers directly feed the plants in your garden. Plant feed fertilizers deliver three main minerals: nitrogen, phosphorous, and potassium. These minerals are the basic building blocks that all plants use to grow. They are also minerals that are easily eroded by wind and rain, or simply used up by the life cycle of plants. Therefore, fertilizer can be of tremendous benefit because it continuously shores up your garden’s supply of these essential minerals.
Each of these minerals has an impact on specific areas of your plants growth cycle:
Nitrogen promotes root growth and helps plants maintain stronger stems and greener foliage.
Phosphorous impacts your plant at the reproductive level, aiding in seedling development, blooms and fruits. This mineral is a must for any floral.
Potassium also helps plants maintain strong root and stem systems. But its more important function is in aiding the production of starches and proteins. This allows a plant to more effectively resist disease and environmental stress on an ongoing basis.
It’s All About Ratios
So how do these key minerals come into play? Well, when you pick up a bag of fertilizer, it will be labeled with three numbers, separated by hyphens, for example: 12-8-10. This is what is known as the "NPK ratio". This tells you percentage of available nitrogen (N), phosphorous (P), and potassium (K) in a given fertilizer’s formula. (K is used for Potassium because that is its symbol on the periodic table of the elements, thus avoiding confusion with Phosphorous).
So an NPK ratio of 12-8-10 tells you that a fertilizer contains 12% nitrogen, 8% phosphorous and 10% potassium.
Here’s another way to look at it: if you had a 100 pound bag of fertilizer, you would have 12 pounds of nitrogen, 8 pounds of phosphorous and 10 pounds of potassium. What about the other 70 pounds? This is comprised of "ballast," or filler material that the minerals bind too, allowing you to spread it in your garden.
You see? It’s really not that complicated.
A good first step is a soil test. This tells you if your soil is too sandy, too thick with clay, or just right. It may be too acidic or alkaline. Once you know what you’re dealing with, you can add an amendment to aid your soil’s composition and get nutrients to your garden more effectively.
Another great way to improve your soil is to leave your annuals in over the winter. It’s surprising how many gardeners pull out their annuals as a way of "cleaning up" before winter. Don’t do it. Let the first frost collapse your annuals just like it would your perennials. The decomposing plant matter will be converted into valuable nutrients by the micro-organisms in your soil.
Secondly, look at what plants populate your garden. Now that you know the key functions of nitrogen, phosphorous, and potassium, you can choose the most beneficial formula, specifically for your garden.
For example, if you have a lawn, nitrogen will be the key ingredient in helping it build a strong root system. If you have mostly flowers, you want to hone in on a formula higher in phosphorous. Then again, maybe the blooms are wonderful, but a good rainstorm or hose spray sends your flowers toppling. That’s a sign of a weak stem so a formula higher in nitrogen is a good bet.
Maybe your garden is just fine, thank you. Choose a formula with a relatively even NPK split for maintenance.
Liquid or Granules? Organic or Synthetic?
Fertilizers come in a variety of forms. Which one to use is up to you, but there are some things to keep in mind.
Organic fertilizers such as blood meal, kelp/seaweed, and manure will deliver nitrogen, phosphorous and potassium, but in lesser amounts. You also have no idea of knowing what the exact ratio is. You won’t get the "jump start" effect that you get with a synthetic fertilizer. However, organic fertilizers are more cost effective than synthetic, because they deliver nutrition to your garden for longer periods.
Synthetic fertilizers are slightly easier to work with since they come in granular or fine powder form and you know the exact NPK ratio you are working with. Some solid forms dissolve into water. Synthetics also pack more of a nutrient punch, which allows you to spot treat certain plants depending on their needs. The drawback here is synthetic fertilizers easily burn root systems or leaves if you overestimate the amount.
Most professionals tend to favour solid fertilizers over liquid forms. Solid forms work slower but last longer as they are typically scratched into the soil. A liquid application on the other hand can disappear with the next rainstorm and, contrary to popular belief, a plant won’t drink up a liquid fertilizer in one go. They’ll absorb it gradually just as they would a solid form fertilizer.
Either way, a fertilizer’s packaging tells you how much fertilizer to apply per square foot, how to apply it and how many square feet it should cover.
As for timing, autumn is a great time to start. That way you can reapply fertilizer in the spring and then throughout the season as per package instructions.
Once you start applying fertilizer that is geared towards your garden’s specific needs, the results will be addictive. You’ll have an embarrassment of riches in your own yard. You’ll also discover that you didn’t have to memorize that periodic table after all, and that an NPK ratio can be a gardener’s best friend.