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Guide · Pasture Oversowing · Undersowing · Kikuyu · Soil

Oversowing pasture: why Northland waits for autumn, and the spring jobs that make it work

Spring is when the thin patches show, and the urge to get seed on them is strong. In Northland, it's the wrong time. Why autumn sowing wins in summer-dry country, and the spring jobs that decide whether it takes.

Written September 2026. From a working lifestyle block in Northland, New Zealand.

🌱 The short version

In Northland, spring is for getting ready. Autumn is for sowing.

Spring is when the thin patches show up. After a wet winter you can see exactly where the pugging was, where the weeds moved in and where the grass just isn't there any more. The first thought is to get some seed on it now.

Here in Northland we tend not to oversow in spring. There is a real risk of a dry summer, and young grass plants may not survive it. Best practice is to oversow in autumn, which gives the young plants the wet months to get established before they face their first summer.

That doesn't make spring a wasted season. Most of what decides whether autumn sowing works gets done now: choosing the right paddocks, testing the soil, getting on top of the weeds, managing the grass through summer, and ordering the right seed. This guide covers the spring jobs first, then the sowing and the first grazing.

📖 Words first

Oversowing, undersowing, renewal: which is which?

People use these words loosely, and the difference matters when you read advice, because the authorities use them precisely.

DairyNZ is frank about undersowing. It works well in the narrow window when a pasture has thinned out but hasn't yet been taken over by weeds. It doesn't work in dense pasture, it doesn't control problem weeds, and it's usually a temporary fix. In DairyNZ's trials, undersown paddocks held far fewer plants after five years than paddocks that were sprayed and drilled.

None of that is a reason not to do it. On a lifestyle block, drilling fresh seed into thin paddocks is often the right-sized job. It just means going in knowing it's a top-up, not a new pasture, and choosing the paddocks where a top-up will actually take.

☀️ The timing

Why autumn, not spring, in Northland?

A grass seedling is small, shallow-rooted and has no reserves. What it needs is time: time to put down roots, and time to tiller out into a proper plant before it has to cope with a hot, dry spell.

Sow in spring and the seedling has a few months before summer arrives. In a year with a wet summer, that can be enough. In a dry one, the new plants are still small when the soil dries out, and they die, while the established grass and weeds around them, with deeper roots, carry on.

Sow in autumn and the seedling gets the whole of the wet season. Autumn soil is still warm enough for seed to germinate quickly, and there are months of reliable moisture ahead. By the time the next summer comes round, the plant has had most of a year to get big.

That's why DairyNZ's autumn advice for pasture renewal north of Taupō is to aim to have sowing done by the end of March. Sow too late in autumn and the soil cools off, so establishment slows down and the plants have less time to get strong before the next summer.

There's a Northland-specific reason too. Black beetle is a pest of warm areas, including Northland. The adults chew through the base of young ryegrass plants, and the larvae do the most damage from December to March, worst of all in dry summers. A spring-sown pasture meets that summer when it is at its weakest.

🗺️ Not everywhere is Northland

Where spring sowing does work.

If you're reading this somewhere with reliably wet summers, the rule changes. Seed company guidance is that spring sowing only works where young pasture can count on summer moisture. It's regularly done in places with good summer rainfall, such as Southland, the West Coast and higher-altitude country, and on irrigated land.

So the honest version is not "never sow in spring". It's this: the drier and warmer your summers, the more autumn wins. In Northland, a dry summer is a risk you plan for, not a surprise. If you're not sure how your summers usually go, ask a neighbour who has been sowing on your kind of country for a few years.

🇦🇺 Reading this in Australia?

The seasons line up, but the pasture species, pests and rainfall patterns don't. The principle that seedlings need moisture to get established before their first hot, dry spell holds everywhere. For timing and species, go by your local ag department or agronomist.

🚶 Spring job 1

Walk the paddocks and pick the candidates.

Spring is the best time of year to see which paddocks need help, because winter damage is still obvious and the good grass is growing fast enough to show up the bad patches. Walk each paddock and sort them roughly into three groups. This is a simplified version of DairyNZ's own ranking:

While you're walking, note down for each paddock:

DairyNZ suggests planning pasture renewal 6 to 18 months before sowing. For an autumn sowing, that makes this spring about the right time to start.

🧪 Spring job 2

Test the soil before you buy the seed.

Seed is the expensive part, and it's wasted on soil that can't support it. DairyNZ's first step for any pasture renewal is a soil test for nutrients and pH, then fixing what it finds with fertiliser or lime.

If clover is part of the plan, and on a block it usually should be, Beef + Lamb New Zealand gives these as the soil levels legumes need:

That's the reason to test in spring. Lime is slow. If the test comes back acid, lime put on this spring has months to start working before the seed goes in. Lime put on the week before sowing hasn't had time.

Our soil pH and lime guide covers how to take the sample, what the numbers mean, and the diverse pasture mix we're trying on our own block. It also covers why throwing more seed at a paddock won't get round a soil problem.

🌿 Spring job 3

Deal with the weeds, and watch the kikuyu.

New seedlings can't compete with established plants. Whatever is growing in the gaps now will still be there in autumn, bigger. So:

Kikuyu country is its own case. Many Northland farms are kikuyu-dominant, and there the usual approach is different. You don't try to replace the kikuyu. You sow ryegrass into it each autumn to carry the paddock through the cool months when kikuyu stops growing. The DairyNZ and Northland Dairy Development Trust kikuyu guide says:

So for kikuyu paddocks, the spring job is simple: know which ones they are, and plan to keep them short from the new year.

🛒 Spring job 4

Choose the seed, and book the drill.

Autumn is the busy season for seed and for contractors. Sorting both out early means you're not left with whatever is left over.

What to ask about the seed:

Book the drill. A direct drill puts the seed into the soil, where it has moisture and contact, which is why it beats broadcasting on flat or rolling country. Most blocks don't own one, so find out now who does contract drilling locally, and get on their list for March or April.

At the counter, the most useful thing you can bring is a short description of the paddock: its size, what's there now, what's wrong with it, what grazes it, and whether it's kikuyu. That gets you better advice than asking for "a bag of oversowing mix".

⏳ The exception

If a paddock can't wait until autumn.

Some paddocks are too far gone to leave bare or weedy for six months. Bare soil washes, and weeds fill it. For those, DairyNZ's approach for badly damaged paddocks is not to sow pasture now and hope. It's to sow a summer crop in spring, then sow pasture in autumn. The crop holds the ground and grows feed through summer, and the permanent pasture goes in when the timing is right.

On a small block, a summer crop may be more than the job calls for. The point is the same whatever you do: protect the ground now, and put the long-term seed in when it has the best chance of living. If you do sow grass in spring anyway, sow the smallest area that solves the problem, and be ready to water it or write it off if summer turns dry.

🍂 Come autumn

The sowing itself.

If the spring jobs are done, autumn is mostly timing and a few details:

⚖️ When the authorities seem to disagree

DairyNZ doesn't recommend broadcasting seed onto lowland pasture, because too much of it dies on the surface. Yet Beef + Lamb NZ gives advice on broadcasting sub clover into hill country, using stock to tread it in. That isn't a contradiction. It's two different kinds of country. On steep, summer-dry hill country a drill often can't go, and sub clover is a plant that suits broadcasting. On flat and rolling lowland, where a drill can go, drilling does the job better. Match the method to your country, not to whichever advice you read first.

🐑 After sowing

The first grazing, and the first year.

The most common way to lose a new pasture after all that work is to graze it too early, too hard or too wet.

📲 Keeping track

Keeping track of it.

Pasture work runs on a long clock. You walk the paddock in September, test in October, spray in summer, sow in April, and find out in the following summer whether it worked. By then the details are gone unless you wrote them down:

That's what My Block Hand does. Each paddock has its own pasture notes and grazing history, so the "why" and the "what went on" sit with the paddock they belong to. Add a paddock job for the soil test, for keeping a kikuyu paddock short from January, and for sowing in autumn, and the app will remind you when each one is due. Seed, lime and fertiliser costs go into Finances under their own categories.

📲 Using My Block Hand?

The Paddocks help guide covers pasture notes, grazing history and paddock jobs. The Jobs & reminders guide covers setting a job months ahead so it comes back round at the right time.

🚧 Where this guide stops

What this guide cannot do for you.

This is general information for lifestyle-block owners, written from Northland. It doesn't recommend any seed, cultivar or product, and it can't know your soil, your rainfall or your country. Soil conditions, climate and pests vary a lot even within one district. For sowing rates, species and timing on your own block, talk to your seed supplier, a local agronomist or your fertiliser rep, and bring your soil test.

📚 Further reading

Where the information on this page comes from.

Written September 2026, from a working lifestyle block in Northland, New Zealand. This is general information about pasture sowing. It doesn't recommend any seed or product. For your own block, talk to your seed supplier or a local agronomist.