The Ultimate Guide to Lawn Fertilizer

Grass, like all plants, need nutrients to not only survive but to thrive. And while the soil provides some nutrients, those nutrients become depleted if no new food sources are added.

This is where lawn fertilizer comes in.

What is fertilizer?

Fertilizer is essentially lawn food. It contains essential nutrients that plants need to grow and can be either from organic (made of natural materials) or synthetic sources.

Macronutrients are the big three nutrients that all plants need in larger quantities to grow and are referred to NPK for short.

  • Nitrogen (N) promotes rapid growth and a lush green colour.
  • Phosphorous (P) helps grass develop healthy root systems and is especially vital when starting a new lawn.
  • Potassium (K) boosts your grass’ overall health, disease resistance, drought protection, and cold tolerance.

Micronutrients are the other 14 nutrients that plants need to grow in smaller quantities. Synthetic fertilizers tend to only contain the top three macronutrients (NPK), while organic fertilizers tend to contain lower amounts of macronutrients but higher micronutrients.

Organic fertilizers like compost are also better at feeding the beneficial insects, worms and microbiology that make up healthy soil. (Synthetic nitrogen can actually harm the microbiology, leaving your lawn open to disease.)

What are the benefits of fertilizer?

Fertilizer provides your lawn with essential nutrients that aid growth.

Grass, just like all plants, need nutrients to live and to grow. By adding NPK and micronutrients, you’ll be helping your grass to grow thick and luscious.

A thick and healthy lawn fights off weeds, pests, disease, and erosion.

When grass has all the nutrients they need, grass is healthier. Thicker grass reduces or even eliminates the empty space that weeds take advantage of.

And when grass is healthy, it’s much more resilient to pests and diseases. Healthy grass grows more fibrous roots, which means that the grass holds onto soil better and keeps it from being carried off by rain runoff.

Organic fertilizers support beneficial insects, worms and microbiology in your soil.

A healthy soil ecosystem has many benefits, from breaking down nutrients from natural sources then feeding your lawn. The microbiology supports your plants and helps fight off pests and disease.

What types of fertilizer are there?

Organic vs synthetic fertilizers

Horticultural research going back to the 1920s’ have found that synthetic nitrogen actually reduces the efficacy of organic matter in the soil. Organic matter is hugely important in soil!

As the organic matter dissipates:

  • The microbiology stops breaking down organic matter into nutrients
  • The soil becomes compacted, making it harder for roots to spread.
  • The soil loses its ability to retain moisture, so your lawn needs to be watered much more frequently
  • The nitrogen leaches from the soil, fouling groundwater and causing algae blooms
  • Both soil and nitrogen erode away without the organic matter to help it aggregate

You have to keep applying more and more synthetic nitrogen to get the same results in a never-ending cycle of destruction. Meanwhile, using just a bit of compost once or twice a year will:

  • Improve the quality of your lawn’s soil with more organic matter (ideally, lawn soil contains 3% organic matter)
  • Increase the soil’s ability to absorb and retain the right amount of moisture, allowing you to water less and also not have big puddles sitting on your lawn
  • Feed your lawn both in the short-term and long-term, months after slow-release synthetic fertilizers have washed away, while nutrients stay where you want them – on your lawn, not in the groundwater
  • Support the beneficial microbiology, insects, and worms that will help your lawn become healthier and better able to fight off pests and disease

Basically, when you use synthetic fertilizers, you make your lawn much harder to care for! So do yourself, your wallet, and your weekend a favour and stick with compost.

Organic fertilizers

Compost

Compost is pretty much all you need to grow a beautiful, lush lawn, and you can make it for free!

Compost is natural materials like grass clippings, dead leaves, yard scraps, and kitchen scraps (or even manure) that is being broken down by worms and microbes into nutrients that feed plants. When the decaying matter looks dark brown, smells like loamy earth, and crumbles easily in the hand, then it’s finished and ready to use on your lawn.

If you’re looking for a boost in phosphorus for establishing a new lawn or other macro and micro-nutrients, then you can also add amendments like:

  • Alfalfa meal for a boost of NPK
  • Kelp meal for micronutrients and plant growth hormones
  • Bone meal for a boost in phosphorus, calcium, and nitrogen

With synthetic fertilizers, you have to be careful not to apply too much or the excess nitrogen will burn your plants. You don’t have that problem with compost.

Don’t worry – you don’t need to mix compost into your lawn soil to get the benefits. You just need to topdress your lawn by ¼”. It’s really easy to apply:

  • By hand: take handfuls of compost and scatter them over your lawn until you get a ¼” layer of compost. (Best for small patches.)
  • By rake: dump piles of compost throughout your lawn and rake it to an even ¼” thickness.
  • By fertilizer spreader: set the spreader to a low thickness. Take multiple passes in each direction to ensure the compost is evenly distributed to only ¼”.

Check out our Composting 101: Definition, What to Compost & How to Start DIY Composting Guide for Beginners to learn everything you need to know to get started.

Grasscycle

Grasscycling couldn’t be easier! Just leave grass clippings on your lawn after mowing.

According to Kansas State Research and Extension, by leaving grass clippings, you can:

  • Return up to 25% of nutrients (including nitrogen) back into the soil
  • Reduce time spent mowing by 33%
  • Reduce your household waste by 10%

Mow often so you don’t need to take off more than an inch of a time and avoid mowing when the grass is wet to avoid grass clumps. If the grass clippings do clump up, break the clumps up so that sunlight can get to the grass underneath.

However, if your grass has leaf spot, rust spot or dollar spot, then remove the grass clippings for the trash to reduce the spread of the disease.

If you don’t like the idea of leaving grass clippings on your lawn, then gather them up for a compost pile.

Synthetic fertilizers

Quick-release

Quick-release is exactly what it sounds like – the fertilizer (usually nitrogen) is quickly released to the plants when it’s dissolved in water. The downside is that they quickly leach away, lasting only two-to-four weeks.

Slow-release

Instead of quickly releasing, they slowly release nitrogen into the lawn over 6 to 8 weeks. They provide more uniform grass growth and are less likely to burn the grass from overapplication.

The downside is that they’re:

  • More expensive than quick-release
  • Work less well in cold soil
  • Require more irrigation in hot weather, which means they don’t last as long.

Granule vs liquid fertilizer

Granule fertilizers are dry pellets while liquid fertilizers are liquid, and while there seems to be no difference between them in delivering synthetic nutrients to plants, there are pros and cons for you, the person applying them.

Liquid fertilizers are:

  • faster acting (but won’t last long),
  • can blend with other liquid fertilizers, and
  • harder for non-professionals to apply evenly.

Granular fertilizers are:

  • cheaper to buy in bulk,
  • easier to store (so if you have leftover fertilizer, you can keep it until next year),
  • available as slow-release, and
  • easier for non-professionals to apply evenly.

Starter Lawn Fertilizer

Starter lawn fertilizers are specially formulated to help your lawn get started, with more phosphorus to encourage the development of healthy root systems.

If you want to keep organic, then you can increase the phosphorus content of your compost with bone meal and/or by composting banana peels, grains, nuts, and eggshells.

Weed and insect control

Synthetic weed or insect control fertilizer is just fertilizer combined with herbicides or pesticides. It may seem like it’ll save time, but herbicides and pesticides can be really harmful to your health and the environment around your yard.

There’s a ton of easy and natural ways to keep down weeds, and if you do need to use herbicide or pesticides, it’s best to spot-treat to pick the most effective treatment and limit unintended consequences.

When and how often should you fertilize your lawn?

The minimal lawn fertilizer schedule

If you want to keep lawn care minimal, the best time to fertilize your lawn is in late-summer (warm-season grass) or fall just before the trees drop their leaves (cool-season grass).

A late in the season feeding will help your lawn strengthen their roots and increase nitrogen storage for a headstart in the spring.

Compost works best on this kind of schedule.

The twice-a-year lawn fertilizer schedule

But if you’re using synthetic fertilizer rather than compost, then you’ll need to apply more often. (Compost can also be applied twice a year if you really want.)

This can be where lawn fertilizer schedules can get crazy, with different experts recommending fertilizing up to 5 times a year. But really, you just need to keep one rule in mind:

Fertilize only when your grass is actively growing.

And if you want one more rule to temper that one:

More is not necessarily better. More than four treatments a year is just wasting money, increasing how much you have to mow, and increasing fertilizer runoff, which can have devastating effects for your soil, your local environment and wildlife.

If you have cool-season grass:

Cool-season grasses, as the name suggests, have their peak growing periods during the cooler season, in the early spring and early fall. During the heat of summer, this grass goes dormant by going brown.

Fertilize cool-season grasses lightly in the spring and heavily in the fall. Avoid fertilising in the summer when the grass is dormant.

If you have warm-season grass:

Warm-season grasses come from the tropics and are favoured in southern, hot regions. Their peak growing season is during the heat of midsummer.

Fertilize warm-season grasses in late spring when the grass is turning green and again once the peak summer heat has passed.

Warm-season grasses need a lot more nitrogen per square foot than cool-season.

How do you choose the right product?

A good rule of thumb with all gardening and yard care is to go with natural, organic solutions first, and only use synthetic solutions when necessary.

Lawn care companies want you to think that taking care of your lawn is difficult and you must use specialised fertilizers to achieve the perfect lawn because it’s more profitable for them if you buy 6 different fertilizers than a few bags of compost.

Compost is the best all-around fertilizer you can choose. Adding a light ¼ layer of compost once a year will help feed your lawn all year long, without the drawbacks of synthetic fertilizers.

Likewise, grasscycling will help return nutrients back into your soil at the right times (when the grass is actively growing). You may want to bolster this with a yearly application of compost.

And if you do want to go with synthetic fertilizer, then figure out what type of grass you have (warm-season or cool-season) and your schedule.

Types of fertilizer spreaders

Spread by hand

Yes, you don’t even need any tools to spread compost or synthetic fertilizer! While wearing gloves, just pick up handfuls and cast it over the lawn like you’re throwing seeds in a historical drama.

This technique is best used when you have a small lawn.

Rake and wheelbarrow

If you have a small or medium-sized yard, you can dump piles of compost throughout your yard, then use a rake to spread it evenly. And really, you don’t even need the wheelbarrow if you’ve bought bagged compost.

Spreaders

A spreader is basically a pyramid container (or hopper) on wheels with holes in the bottom. Spreaders come with a gauge to allow you to make these holes bigger or smaller which changes how thicker the product is applied on your lawn.

You add the compost or fertilizer to the hopper and as you move it over your lawn, the product drops through the holes. Underneath, a flow lever opens and closes a plate under the holes to control when the material drops.

Drop Spreaders

Drop spreaders work best with small yards or when you need very particular placement, like alongside paths or flower beds.

The drop spreader only drops fertilizer or compost directly underneath it, which makes it more difficult to get even coverage and avoid visible striping.

Broadcast Spreaders

If you have a yard over 4,000 sq ft, then it may be time to invest in a broadcast spreader.

Unlike a drop spreader, a broadcast spreader has an extra part: an impeller plate. As one wheel moves, it triggers the impeller plate to catch the fertilizer or compost and cast it over a wider area.

Conclusion

Lawn care, and fertilizing schedules, don’t have to be difficult or complex. By fertilizing your lawn once or twice a year with compost, you too can grow lush, healthy grass.

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Jill Sandy

Jill Sandy

Jill is a sustainable focus gardener. She loves decorating her home backyard with beautiful landscape design and creative garden care techniques she develops herself. You can reach her at [email protected]

Chanh Ho (MD, MPH)

Chanh Ho (MD, MPH)

Chanh is our Head of Medical Review. He is a research physician at Oxford University Clinical Research Unit. After accomplishing the program of level 1 sub-specialty in Pediatrics, he was awarded the Chevening Scholarship for his Master’s degree of Public Health in the University of Edinburgh in 2019

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