October 21st, 2021 by Chris Chapman

Getting a pristine green lawn isn’t a matter of simply watching grass grow. Gardening is an exact science, so there’s a bit of work you’ll need to do to make each blade of grass grow lush and green. Just like any living thing, grass can survive using almost any nutrients – but if you want it to grow strong and healthy, you need to make sure it’s getting the right balance of nutrients.

Luckily, this balancing act is much easier than you might think. The two main nutrients grass needs to grow lush and green are iron sulphate and nitrogen. They’ll help each blade retain more moisture, which causes them to grow thicker and softer. As a byproduct, this also gives your lawn that rich green colour.

Why Do I Need to Feed My Lawn?

Having a lawn full of thick, richly-coloured grass is, to many people, its own reward! If you pride yourself on the way your garden looks, a thriving lawn should be its centrepiece. However, there are many more benefits than simple aesthetics. If your grass is green, this shows it’s strong and healthy. Healthy grass is much more able to fight off pests, disease, frost, and drought, so you won’t be left with yellowed or bare patches on your lawn throughout the year.

In the case of iron sulphate, it also offers benefits beneath the soil. As it makes your grass healthier, it promotes more vigorous root growth. These roots bind the soil together, creating harder turf that feels more comfortable underfoot and is less likely to be deformed by the weather. This means iron sulphate is a key component of any professional grass maintenance routine, especially on sports pitches and golf courses.

Another less well-known benefit is that iron sulphate raises the acidity of the soil very slightly. This makes it less appealing for pests such as chafer grubs and leatherjackets. While it won’t eliminate them completely, it does deter enough to ensure your lawn doesn’t become completely infested.

What is Iron Sulphate?

The first lawn nutrient we’ll discuss is iron sulphate, which is something that comes in many forms. One of those forms – commonly sold as ferrous sulphate to avoid any confusion – is a popular vitamin that you may have seen in health stores. The form that you use in your garden comes as soluble granules, meaning they dissolve in water. It is absorbed into the grass via the root, so needs to be watered down into the soil to take effect. You can also buy liquid iron sulphate, which gives you a bottle of pre-dissolved granules – more on this later.

2.5kg Pro-Kleen Iron Sulphate - Greens Grass, Hardens Turf

Price: £13.96

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How Do I Apply Iron Sulphate?

Iron sulphate is very simple to apply. There are two ways to do it.

The best way is to dissolve the required amount of granules in water (see below for the measures) and apply this solution to your lawn using a watering can or a pump sprayer. Once applied, water the solution down thoroughly into the soil. We recommend applying just before rain is forecast to help with this.

You can also apply the granules neat onto the lawn, without first dissolving them. We don’t recommend this unless you have no other choice, however, as it’s much more difficult to ensure an even spread and the granules won’t penetrate the soil as effectively.

How Much Iron Sulphate Should I Mix?

This depends on how large your garden is and on what your aim is. If you just want greener, healthier grass, this only requires a weaker mix than if you want to harden the turf of a sports pitch.

• Use 1g to 2g per litre of water per square metre for greener grass (100 to 200g for 100 square metres)
• Use 2g to 3g per litre of water per square metre for turf hardening (200 to 300g for 100 square metres)

As an example, if you need to green 10 square metres of grass, mix 10-20g of granules with 10L of water.

When Should I Apply Iron Sulphate?

You can apply iron sulphate at almost any time and it’ll have some benefit to your grass. However, for the very best results, we recommend applying in cooler (but not freezing) temperatures, when there is as much moisture as possible in the soil. If you have a regular lawn watering routine or a sprinkler system that you use often, this gives you the freedom to apply at almost any time of day. If you don’t, we recommend applying early on a dewy morning. You can also apply a few hours after thoroughly watering your garden with a hose, or just after (or even during, if you’re committed) a rainstorm.

As mentioned previously, rainfall helps the dissolved granules work their way down to the grass roots more effectively. This means that, if you can apply just before rain is forecast, it’ll deliver the best results. As you might expect, your chances of applying at the perfect time – between two rainstorms, when it’s cool and there’s plenty of moisture already in the soil – are much higher in autumn through to spring. In summer, this might be a little more awkward if you don’t have the means of regularly watering your lawn.

When Not to Apply Iron Sulphate

All of the above comes with a few caveats. High temperatures can effectively increase the potency of iron sulphate, which means that, on very hot days, mixing a high concentration of 4-5g per L can scorch the grass. You might think applying a lower concentration on a hot day is a good idea because you get more bang for your buck, but as it gives unpredictable results it’s often not worth the risk.

On the other side of the coin, you shouldn’t apply on frosty or icy days. This is because the granules won’t penetrate below the frozen ground, and trying to water them in just results in more ice and damage to the grass.

To summarise, we recommend using no more than 1g per L water on very hot days. If you’re using 2-3g per L, you’ll want to wait until a mild morning with lots of ground moisture. If you use any higher concentrations than this, it’s best to wait until it’s cool and wet.

How Often Should I Apply Iron Sulphate?

We recommend applying iron sulphate once or twice per season – around every 6-8 weeks on average.

Liquid Iron Sulphate

Our iron sulphate is available in two forms – granules, which you have to dissolve yourself, and a liquid form. Liquid iron sulphate is exactly the same formula with all the same benefits and use cases as the granules described above, but it’s pre-dissolved in water. You should apply it the same way, at the same time, and at the same intervals as the granules, but you can skip the step where you dissolve it in water. However, our liquid formula comes with a unique benefit – it has added seaweed extract!

Seaweed is something of a miracle substance for lawns. It’s packed with vitamins and nutrients as well as other good stuff like sugars and growth hormones – significantly more than you’ll find in land-based plants. It also helps stimulate bacteria growth in the soil, which further benefits your lawn. These bacteria break down organic matter beneath your grass, enriching the soil with lots of easy-to-absorb nutrients.

5L Liquid Iron Sulphate Lawn Tonic

Price: £16.96

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Grass Green Lawn Fertiliser

Of course, iron sulphate is just half of the story. The other piece of the lawn care puzzle is Grass Green – our high-nitrogen lawn fertiliser. Nitrogen is one of the essential building blocks of plant life – and all life on Earth, as it makes up almost 80% of our atmosphere – as it’s an element that plants need to grow. Any nitrogen is good for the grass, but our Grass Green formula has a few unique features that make it extra-useful.

A Blend of Ingredients

Grass Green is 22-5-10 NPK fertiliser. The numbers show what percentage of the formula is made up of each ingredient, and the NPK shows the chemical symbols of the three main elements – nitrogen (N), phosphorous (P), and potassium (K). The extremely high 22% nitrogen content sets Grass Green apart from other brands, promoting vigorous healthy growth in every blade of grass and providing nutrients long after application (more on this later). Phosphorous helps promote strong root growth in the grass and helps it photosynthesise (turn sunlight into energy) more efficiently. Finally, potassium also assists in plant growth and strength and, crucially, it helps grass use nitrogen more effectively. This carefully balanced blend of nutrients is packed into every granule of Grass Green, making it a professional-grade formula that provides optimum nutrition to grass.

Slow-Release Formula

Most NPK fertiliser will be beneficial to your lawn for a little while, but it needs to be applied every few weeks – every month at a push – to get the most from it. This is because the grass will initially feast on the nitrogen, burning through it very quickly. Of course, this means it’ll soon be left with no extra nitrogen when it might be vulnerable to pests, frost, or drought. This feast or famine cycle means your lawn will go through peaks and troughs when it comes to its health, which isn’t great for your garden and it certainly isn’t acceptable when it comes to sports pitches and commercial lawns.

Grass Green avoids this problem entirely. It uses specially-formulated granules that release nitrogen slowly over time. This means a treatment lasts three times longer than traditional NPK fertiliser does, so you only need to use it once every three months. The nitrogen release is triggered by demand from the grass roots - minute changes in the soil temperature and the activity of microorganisms in the soil signal when the grass needs some nutrients and trigger the release.

Pro-Kleen Grass Green Lawn Fertiliser 2.5KG

Price: £16.96

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How Do I Apply Grass Green Fertiliser?

The application of Grass Green is incredibly simple. Simply measure out the required amount of granules (measurements below) and sprinkle them evenly across the whole surface area of your lawn. If rain is forecast, leave nature to water them down into the soil for you. If no rain is forecast, use a hose or watering can to water them down thoroughly. You can apply it by hand or in a garden spreader.

How Much Lawn Fertiliser Should I Use?

Thanks to the way it breaks down in the soil, precise measurements aren’t as important with Grass Green as they are with iron sulphate. However, it is still possible to use too much - as with any NPK fertiliser, this can result in excessive thatch, causing the grass to smother itself.

• Use 25g Grass Green per 1m² of grass.
• Use 250g Grass Green per 10m² of grass.

When Should I Apply Grass Green?

With NPK fertiliser, you need to vary your doses through the changing seasons. This is because grass grows more in spring and summer, so it has more need for nitrogen. In winter, when the grass is mostly dormant, it’s easy to overload the soil, promoting excessive growth which leads to heavy thatch, which in turn leads to big brown patches of sickly grass. We recommend you apply from spring through to autumn, but don't apply in winter as it'll result in what's known as "soft growth" - unnatural growth that makes the grass more vulnerable to disease and scorching.

How Often Should I Apply Grass Green?

As mentioned above, the slow-release formula remains active for up to three months (110 days to be exact). This means applying once every three months will keep your grass lush and green all year round.

Using NPK Fertiliser Near Lakes and Water Sources

NPK fertilisers should be used with great care near ponds, lakes, and other water sources that are home to wildlife. They aren’t directly harmful to plant or animal life but if used in large enough quantities, some of the nitrates can leach from the ground into the waterways. If they reach a body of water, they’ll feed algal blooms and other plants which will grow on the water’s surface. This blocks sunlight from entering the water, causing other plant life to die and which, in turn, causes the animals that depend on this plant life to die too.

This is a gradual process and can be managed with care. If you only plan to use your fertiliser on a domestic garden, though, it isn’t really a concern. Even if you do happen to live near a water source, you won’t use the fertiliser in anywhere near the quantities required to affect the groundwater.