If you have a garden, at some point you’re going to need to fertilize it, right?

Not necessarily.

Fertilizer isn’t actually a routinely necessary part of gardening.

So the question of how often to fertilize the garden should probably actually be when and why.

To answer these questions, it’s important to understand a bit about soil health, the differences between organic and synthetic fertilizers, and also the different fertilizer requirements of different parts of your garden.

So, let’s get started!

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What is Fertilizer?

Fertilizer is a concentrated source of the nutrients that are required by plants for healthy growth.

The main nutrients that make up a garden fertilizer are nitrogen (N), phosphorus (P) and potassium (K). Different fertilizers come with varying ratios of these macronutrients, usually described in number form on the packaging (eg. 4-5-7).

You’ll want to choose a fertilizer that has roughly even ratios of each of the three main nutrients unless you’ve identified a specific deficiency in your soil.

Secondary macronutrients are nutrients utilized in slightly lower amounts by plants. These include calcium, sulfur and magnesium.

After this, there are also micronutrients utilized in even smaller amounts, including boron, copper, nickel, chlorine, iron, manganese, molybdenum and zinc.

person in yellow gloves holding granual fertilizer

Fertilizer can be composed of nutrients from organic sources such as animal manure, blood, bones and compost, or synthetic nutrients, synthesized or isolated artificially in a lab.

Organic Versus Synthetic Fertilizer

If you look purely at the nutrients involved, both organic and synthetic fertilizers contain the same nutrients.

However, organic fertilizer comes with the nutrients in their whole, unadulterated package, complete with all of the other organic molecules needed to support soil health over time. Synthetic fertilizer on the other hand is literally just the nutrients delivered in a quick, easy to absorb formula.

How to Know Which is Better

Organic fertilizer is like eating a loaf of wholemeal sourdough bread. The nutrients are delivered in their unprocessed form and the energy is released slowly over time, supporting your health and blood sugar levels.

Meanwhile, synthetic fertilizers are like highly processed white bread. You get a really quick fix of energy as the sugars are released but there are few, if any, other benefits, and you’re back to where you started pretty quickly.

Synthetic fertilizers are absorbed very quickly by the plant, which causes a quick burst of growth and apparent health that doesn’t always result in a vigorous plant.

While the plant can appear healthy from the outside, all of that new foliage may be supported by immature, or weak roots that are lagging behind.

Furthermore, synthetic fertilizers don’t support soil health or structure. Over time, synthetic fertilizers actually degrade soil health and structure, resulting in soil that is devoid of nutrients and can’t hold on to water.

This usually means that people end up applying even more fertilizers to their gardens, thinking that this will remedy the situation. Unfortunately, it only makes it worse, and the consequences for the environment are worse too.

Excess synthetic nutrients from fertilizers run off into local waterways causing environmental problems such as algal blooms, and a buildup of nitrates in groundwater supplies. Meanwhile, excess water runs off from the degraded soil causing erosion and potential flooding.

Making the Decision for Organic Fertilizer?

Organic fertilizers support soil health and structure, improving the quality of your soil over time by feeding all of the beneficial microbes, so that, if managed effectively, you should be able to reduce the number of fertilizer applications needed in the future.

person fertilizing lawn with liquid fertilizer

Healthy soil holds on to water more effectively, and the abundance of healthy soil microbes and earthworms make short work of breaking down mulch and compost, making it easy to keep your soil healthy and jam-packed with nutrients without the need for fertilizer.

The only times you might resort to synthetic fertilizer are if you have a big crop of vegetables that are really struggling and are in need of a quick boost before the growing season ends and you lose your crop.

This would be a one-off application with the aim of salvaging some produce from your hard work, but it shouldn’t be a regular practice.

When and What Do You Need to Fertilize?

How often to fertilize your garden depends on the kind of garden you have and the health of your soil.

If you’re not growing vegetables but instead have an ornamental garden of flowers and shrubs, you should be able to manage the majority of your garden’s nutrient needs simply through mulching.

Contrary to popular belief, ornamental gardens do not need fertilizer. Fertilizer developed especially for plants such a roses is simply marketing. Provided you’re keeping a healthy layer of mulch on the ground (and most of the time, even without this), if your plants are growing, you don’t need to fertilize.

The exception to this would be container or pot plants where the soil will get depleted over time.

What About the Lawn?

Similarly, a healthy lawn also shouldn’t need fertilizer.

If your lawn is struggling and needs a helping hand, then applying some organic fertilizer at the beginning of its growing season is a good idea. However, if you’re supporting lawn health naturally, for example by including clover in your lawn and spreading grass clippings, then you should never need to fertilize it.

If you are dead set on your lawn to be composed of just one grass species, then you will likely need to fertilize it once or twice per year as it’s unlikely to be able to sustain itself naturally.

When Should You Fertilize Your Lawn?

Stick to fertilizing during periods of high growth.

When this is will depend on what kind of grass you have and what kind of climate you live in.

For example, cool-season grasses like Kentucky Blue, Rye, and Fescue, should be fertilized in the fall, while warm-season grasses like Bermuda, Zoysia or Buffalo, should be fertilized in the late spring or early summer.

Fertilizing when your grass is dormant is basically like pouring money down the drain. If your lawn is healthy, once per year should be enough.

And remember, you should never fertilize a lawn with synthetic fertilizer. It will be recipe for disaster further down the track.

If you’re in charge of a very large lawn, using a tow behind sprayer will make short work of applying liquid fertilizer. There are plenty of organic fertilizers available in liquid form, for example, seaweed-based solutions.

Alternatively, using a spreader can be used for both granular fertilizers as well as seeds if your lawn needs a re-seeding, making it a versatile option.

If you’re not sure whether you’re after liquid or granular fertilizer, have a read of this weigh in on the subject.

What About the Vegetable Garden?

Vegetable gardens do need a little extra love!

Vegetable gardens, especially if you’re growing all year round, take a lot out of the soil. And what’s taken out needs replacing.

Ideally, practicing no-dig or lasagna gardening and regularly adding layers of mulch and compost to your garden should maintain optimal soil health and you shouldn’t need to add fertilizer.

However, if you’re starting out and your soil health isn’t where it needs to be yet, then organic fertilizer will give your vegetable garden a much-needed boost until it’s healthy enough to survive happily with regular mulching.

granual lawn fertilizer

Furthermore, summer fruiting crops like tomatoes are heavy feeders. If you want to maximize fruit yields then giving your summer crops a feed is a good idea.

Vegetable garden fertilizer recommendations should be focused on high-quality, organic ingredients like animal manure, seaweed, blood, and bones.

Remember to protect yourself with gardening gloves and a mask when fertilizing. Organic compost can contain live organisms and pose risks for diseases such as legionnaires.

In a Nutshell

  • Ornamental gardens don’t need fertilizer.
  • A healthy lawn also shouldn’t need fertilizing. But if your lawn isn’t completely healthy, or you’re trying to support a mono-crop, then fertilizing once per year in its period of high growth is a good idea.
  • Vegetable gardens should only need fertilizing if your soil isn’t at optimum health yet, or if you have a bunch of heavy-feeding summer crops and want to maximize harvest.

FAQ

How often should you fertilize?

Fertilizer companies will tell you that you need to fertilize multiple times per season, or throughout the year.

Then again, fertilizer companies also tell you that you need to fertilize your ornamentals (which you don’t!).

In reality, there is no hard and fast rule. How often you fertilize is going to be based on your individual circumstances and it will change over time as your garden (hopefully) gets healthier.

If you’ve just moved to a new property and the soil is in dire straits, then giving your ornamental garden, lawn, and veggie garden a feed with a good quality organic fertilizer won’t do any harm and will get you off to a good start.

Long term, your ornamentals should need nothing except mulch and water, your lawn should need no more than one application per year, and your vegetable garden should need no more than a couple of applications, and only in summer.

Fertilizing anything when it doesn’t need it is a bad idea. You could end up with fertilizer burn and plants (or grass) that is less healthy than it was before! In fact, fertilizing too much is more damaging than not fertilizing enough. So, if in doubt, don’t!

Is it possible to over-fertilize?

Yes.

As mentioned above, over-fertilizing actually harms plants and the surrounding environment. Aside from the fact that you’re wasting money, your plants could end up weaker and more vulnerable to disease and pests.

Excess fertilizer is also more likely to leach into local water bodies causing imbalances in the ecosystem.

Rather than routinely applying fertilizer without a second thought, it’s best practice to observe your garden and look for signs of nutrient deficiencies, or slow growth in what should be a peak growth season, and then apply fertilizer as a remedy.

To know for sure what you’re working with, the best thing you can do is get a soil test done. If you don’t want to do this, then keep an eye out for signs of trouble such as pale green leaves, yellowing of foliage or stunted growth.

Understanding all of the different signs of nutrient deficiencies in different plants is more involved than I have space to get into here, but figuring out what your particular plant, lawn or vegetable crop is lacking can save you time, money, and wasted fertilizer.

Can you overfertilize your vegetable garden?

Yes! You can over-fertilize anything. But with a vegetable garden where different vegetables are taking different amounts of different things from the soil, you run the risk of creating further imbalances if you over-fertilize.

For example, your soil may have plenty of nitrogen but be deficient in magnesium. If you go adding a nitrogen-rich fertilizer, your garden will not be happy!

Do some digging (ahem, Googling), look at the symptoms that your plants are displaying, and attempt to remedy them specifically rather than just applying a broad spectrum fertilizer. For example, Epsom salts are an excellent source of magnesium!

Summary

As you can see from all of this information, fertilizing is a bit of a science.

But, in saying that, it’s important to remember that fertilizer is still a fairly recent invention, and back in our grandparents’ day, they were perfectly fine with their compost and manure.

Supporting good soil health should be your priority. Using fertilizer should be seen as temporary support on the way to good soil health.

Feel free to share your thoughts in the comments below!