Applying liquid fertiliser

Liquid fertilisers are mixed with water and sprayed on. Some of the nutrients are taken up through the leaves and some through the soil, which is why the colour response is usually quick. Because the effect is shorter than a slow-release granular, they’re applied more often or used as a top-up between granular feeds. This guide covers when to use them, how much, how to spray them evenly, and how to avoid the most common problems.

When liquid fertiliser makes sense

Liquid fertilisers suit:

• a quick green-up, for example before an event or after a lawn has recovered from stress;
• top-ups between slow-release granular feeds;
• small or awkward lawns, where a hose-end sprayer is easier than a spreader;
• lawns where granules are hard to keep off paths, such as narrow strips beside driveways.

They’re less suited to being the only feed for a large lawn through the whole season, because they need re-applying more often. Read Liquid or granular fertiliser? for a side-by-side comparison.

Read the label first

The label tells you:

• the rate, usually as an amount of product per area;
• how often you can re-apply, and any maximum number of applications;
• whether to water in, and when;
• conditions to avoid, such as heat, drought stress or rain;
• the analysis: the nutrients it contains. Liquid fertiliser labels may state the analysis by weight per volume (w/v) rather than weight per weight (w/w), so compare products carefully. What does NPK mean? explains the numbers.

What’s in the bottle

The three numbers on a fertiliser label are the main nutrients: nitrogen (N), phosphorus (P) and potassium (K).

• Nitrogen drives leaf growth and green colour. It’s the nutrient lawns use most, and the one that does most to change how a lawn looks.
• Phosphorus supports roots and establishment. Established lawns on many soils need little of it, and it’s the nutrient of most concern when fertiliser washes into waterways.
• Potassium helps the grass cope with stress such as heat, drought, cold and wear.

Many lawn products also contain iron, which gives a quick darkening of colour, and other trace elements. A soil test, covered in the soil testing guide, tells you whether your soil is actually short of anything.

Types of liquid product

Not every liquid sold for lawns is a fertiliser in the same sense.

• Soluble fertilisers are concentrated nutrients that dissolve completely. They give the fastest response and the label lists a full analysis.
• Organic-based liquids, made from materials such as fish or manure, release nutrients more gently. Their analysis is often lower.
• Seaweed and humic products are usually sold as soil conditioners or plant tonics rather than as a main source of nutrients. They can be useful alongside a fertiliser, but check the analysis before relying on one to feed the lawn.

Whichever you choose, the label rate and timing still apply.

When to apply

Apply while the lawn is actively growing, which for warm-season grasses is spring to autumn. Feeding a dormant lawn in winter in cooler zones mostly wastes product.

Avoid:

• heatwaves and the hottest part of the day;
• just before heavy rain, which can wash product off the lawn and into drains;
• waterlogged or drought-stressed lawns.

Early morning or late afternoon on a calm day is ideal.

How much

The label gives the rate per area and how often you can re-apply. Measure your lawn with the Lawn Area Calculator, then use the Product Application Calculator to convert the label rate into an amount for your lawn. If the label gives a water volume, the calculator works that out too.

More is not better. Too much fertiliser can scorch the leaves, and any excess nitrogen that the grass can’t use is at risk of washing away.

Applying with a hose-end sprayer

Most liquid lawn fertilisers are designed for hose-end application.

1. Put the amount for your lawn in the jar, and set the dial from the label and the sprayer maker’s chart.
2. Do a quick water-only trial to check your pace covers the lawn with the jar.
3. Start at the far end and spray in parallel strips with a slight overlap, edges first.
4. Keep moving at a steady pace and turn the sprayer off when you stop.

The hose-end sprayer guide covers setup in detail.

Applying with a pump sprayer

For small areas, or where the label gives a specific water volume, a calibrated pump sprayer gives more control. Calibrate with water first so you know how much your sprayer puts out per area at your pace, then mix the product for exactly the area you’re treating. If you also use the sprayer for herbicides, clean it thoroughly first, or better, keep separate sprayers.

Watering in

Follow the label. Some liquid fertilisers can sit on the leaf for a period before irrigation; others should be watered in. If the label doesn’t say, check the manufacturer’s product information before you water, and don’t apply right before heavy rain.

Don’t overwater afterwards either. Water authorities note that watering more than the lawn needs can leach nutrients out of the soil, which wastes the feed you’ve just applied.

Mixing with other products

Only mix products when both labels allow it, and follow their mixing order. If either label is silent, apply them separately. The tank mixing guide explains why.

Protecting drains and waterways

Fertiliser that lands on paths, driveways and gutters is washed into stormwater drains by the next rain, and from there into creeks, rivers and the sea. Research on residential stormwater has found that larger and longer rain events carry more nitrogen from fertilisers off urban properties.

• Spray away from hard surfaces, and do the edges carefully.
• Rinse any drips off paths onto the lawn.
• Check the forecast and avoid applying before heavy rain.
• Never rinse equipment into a drain.

A simple feeding plan

Many lawns do well with a slow-release granular feed in spring and early autumn, and a liquid top-up in between if the colour fades. The right plan depends on your grass, your soil and how you use the lawn. Zoysia generally needs less feeding than buffalo, couch or kikuyu, and kikuyu responds strongly, which also means more mowing. Use the Lawn Calendar for your zone to see the feeding windows, and let your Lawn Journal remind you when the next feed is due.

Signs of too much or too little

• Too little: pale or yellowing leaves across the whole lawn while it should be growing, and clover moving in.
• Too much: scorched tips after feeding, very fast soft growth that needs constant mowing, and more disease in humid weather.
• Neither: yellowing in patches usually has another cause, such as dry soil, grubs or uneven watering. Read Why is my buffalo going yellow? before reaching for more fertiliser.

Feeding new and recovering lawns

New turf: follow the turf supplier’s instructions. Many recommend a light feed once the turf has started to root, not on the day it’s laid, and the label may say whether the product suits new turf.

After stress: a lawn coming out of a drought, a heatwave or a grub attack needs water and time first. Once it’s growing again, a light feed at the label rate helps it thicken. Feeding a stressed lawn harder can make things worse.

After renovation: once scarified or cored lawns start to recover, feeding at the label rate helps the grass fill the gaps. Check the label of any pre-emergent you’ve used before renovating.

Your checklist

1. Lawn actively growing? If not, wait.
2. Label read: rate, interval, watering in, conditions to avoid.
3. Lawn measured and amount worked out with the calculator.
4. Sprayer set up, and a water-only trial done.
5. Calm, mild day with no heavy rain forecast.
6. Edges first, then parallel strips, keeping spray off hard surfaces.
7. Watered in if the label says so.
8. Sprayer rinsed, product stored, application logged.

Safety

Wear the gloves and eye protection the label lists while handling the concentrate. Keep children and pets off the lawn until the spray has dried or the label’s conditions are met. Store the product in its original container, out of reach.

Common mistakes

• Applying more often than the label allows because the colour fades.
• Spraying in the heat of the day, when leaves are more likely to scorch.
• Mixing it stronger than the label rate in the hope of a better result.
• Spraying onto paths and driveways, where it washes into stormwater drains.
• Feeding a dormant lawn in winter in cooler zones, when the grass can’t use it.
• Feeding to fix yellowing that’s caused by something else.

Record it

Log the product and amount in your Lawn Journal. If we have the product’s analysis on file, the journal adds up the nutrients you’ve applied this year, so you can see whether you’re feeding more than you think.