When to fertilize your lawn in spring? Lawn experts share their advice

Experts agree that knowing exactly when to fertilize your lawn in spring can make a huge difference to the condition of a lawn through summer. Getting the timing right, they say, is key to transforming the thinnest and sorriest area of grass into a dreamy, green sward.

So, how to know when to fertilize your lawn? ‘Spring is the perfect time to fertilize your lawn as the warm temperature and rainy days provide the perfect environment for your grass to grow,’ says Susan Brandt co-founder of Blooming Secrets. ‘However, the exact timing will depend on where you live and the type of grass you have.’ 

We’ve spoken to leading industry and garden experts and here they share their tips on fertilizing a lawn in different zones, taking your grass type into account.

When to fertilize a lawn in spring

First you need to identify if you are in a southern or transitional region, or temperate or northern region. You can do this by checking the USDA hardiness zone map. This should help you understand whether you have cool or warm season grass. Together, this will help you recognize when to fertilize your lawn.

When to fertilize warm season grasses

If you live in the southern or transitional regions, then chances are your lawn will consist of warm season grass varieties such as Bermudagrass, tough and dense Buffalograss, Bahiagrass and creeping Zoysiagrass. 

Actively growing from late spring through to mid fall – September and October – they tend to be more drought resistant than cooler season varieties. 

When it comes to fertilizing this type of grass, getting the timing right is key.

‘Warm season grasses can be fertilized with Milorganite [Ed: available at Amazon] – a slow-release nitrogen fertilizer – when they begin to break dormancy, which is when your lawn begins to grow and green-up, in late winter or early spring,’ says agronomist Jaime Staufenbeil. ‘You’ll know its time to fertilize when daytime temperatures are consistently in the 70s and soil temperatures are in the 60s.’ 

Do try to avoid applying fertilizer too early in the growing season though, as this will promote plenty of leaf growth before the roots have had a chance to strengthen, weakening the grass.

When to fertilize cool season grasses

Commonly found in temperate and northern climates, cool season grass varieties begin to grow in mid spring and stay green until dormancy in late fall. Including types such as Kentucky bluegrass, ryegrass, fine and tall fescue, these dense, turf grasses benefit greatly from feeding due to their lengthy growing period.

‘Fertilizing your lawn in spring can help promote healthy growth, strengthen roots, and increase chlorophyll production which helps your grass stay green throughout the season,’ says Susan Brandt co-founder of Blooming Secrets. 

'In the spring, your grass will start waking up, so you do not need to fertilize it right away. The ideal time to fertilize it is in the late spring right before the summer heat starts. Your grass has been doing well and growth will start slowing from the heat, so the fertilizer will help keep your lawn going and thriving.’ 

Signs it's time to fertilize a lawn

Your lawn, and the weather, will give you clues that it's time to fertilize it: 

When the grass shows signs of growth

One handy way to time the first feed is suggested by Eric Halfman, Go-To-Market Manager, John Deere. ‘The first time should be when your grass is turning green, and the temperature of your soil has warmed. Timing for this usually is close to the first couple mows of the year. Follow your fertilizer bags' application instructions for best performance and results.’ 

After rainfall

Many gardeners like to apply a lawn fertilizer directly after a rainy period, but generally it is more beneficial to wait a day or two to let the water soak into the soil and down to the roots. This will boost nutrient take up from the applied feed. If you have no choice but to apply a granular feed during a dry spell, do check the manufacturer’s instructions. Some products will requiring watering in but others have a special protective coating that enable them to lie dormant until the rain returns. 

After aerating

Ideally, you should always aerate a lawn before fertilizing it. This is best done a couple of days after rainfall when the lawn is moist but not sodden.

The best months to fertilize a lawn

This really does depend on your local climate and grass type. These generally fall into one of two groups: cool season or warm season grasses.

‘“When should I fertilize a cool-season lawn?” is a common question, but the fertilization of cool-season grasses doesn’t have to be complicated’ says Josh Miller, General Manager, Baker Lime. ‘You should fertilize two to four times per year, based on soil testing. The best months are March or May and September or November.’

So, fertilizing a lawn in fall is possible, but warm season grasses are best fertilized when they first come out of their dormant period and begin to produce fresh green growth, in other words, in spring. However, in warm southern regions, where there is no natural rest period, aim to fertilize in April.

How many times a year should a lawn be fertilized?

Warm season grasses should be fertilized three or four times a year: 

• Around March or April when the turf first ‘greens’ up.
• During June before the hot season begins.
• Sometime in September – ideally 6 to 8 weeks before the first frost.

For cool season grasses, twice annually is usually enough. Aim to fertilize:

• Late spring or early summer, after fresh growth has appeared.
• During early fall around 6 to 8 weeks before the first freeze.