Plant grades explained: tubes, 2.5L and PB18 — what are you actually paying for?

Line three plants of the same species up on the bench — a root trainer, a 2.5L and a PB18 — and you’re looking at three very different prices for what might look like one line on a trade list. None of them is a rip-off and none of them is a bargain. They’re the same plant at different ages. What you’re really choosing is how much time you want to buy.

And that’s the whole trick to reading a trade list without getting stung: match the grade to the job, not to habit.

What does a plant grade actually mean?

It’s the container, plus the age and root system that come with it. Nothing more mysterious than that.

A grade isn’t a quality tier. The root trainer Cordyline and the PB18 Cordyline came off the same mother stock and got the same mix, the same feed, the same frosts. The PB18 has just been on the nursery a season or two longer — potted on, watered, weeded, spaced and handled the whole way. You’re paying for that time, not for a better plant.

What do the grade names mean?

The names look like code, but there are only three systems worth knowing:

• Tubes or Root trainers — small plants supplied in trays or bare-rooted. Small on top, excellent underneath. The cheapest way to buy natives by the hundred.

• Litre pots (1L, 2.5L, 5L…) — measured the obvious way, in litres of mix. The 2.5L is the workhorse of the landscape trade: big enough to plant out and be seen, small enough to be economical.

• PB bags (PB5, PB18, PB28…) — the old polythene Pint Bag system. The conversion is roughly 1.8 imperial pints to a litre, so a PB18 is about 10L. Plenty of the trade still thinks in PB sizes, so it pays to know both.

That’s it. Different growers use different systems, which is why the same plant can turn up under two names on two lists.

Is a bigger grade a better plant?

No. It’s an older one.

Think stock, not supermarket: a two-year heifer costs more than a calf, but nobody reckons she’s a better animal — she’s just further along. Plants are the same, with one twist in the smaller grade’s favour.

The twist is that the small grade often catches up. A tube/root trainer native planted in autumn into decent ground will often come level with a 2.5L planted at the same time — establishment is about roots getting away, and a young root system in fresh ground gets away fast. The big grade, meanwhile, spends its first season just getting over the shift.

Which grade suits which job?

Match the grade to three things: the numbers, the deadline and the calendar.

•       Planting by the hundred or thousand — revegetation, shelterbelts, big native blocks — tubes. The per-plant saving multiplied across a whole block pays handsomely for a season of patience.

•       General landscape work — 1L to 2.5L is the sweet spot. Established enough to shrug off the shift, cheap enough to buy the numbers a decent hedge actually needs.

•       Hedges and specimen trees — a client who wants the screen this year, not in three — PB18 and up. You’re buying the years they don’t want to wait.

Then the calendar. Autumn is the best planting window — warm soil, cooling air, roots away before winter — and you can plant small grades with confidence. Winter’s fine too; the ground stays moist and roots tick along. The risky move is planting late, heading into a dry summer — Central Otago especially. If that’s where the job’s landed, go up a grade: a 2.5L or PB18 carries a root mass and water reserve a root trainer simply doesn’t have. Late planting is when small grades get hurt.

Where does the money actually go?

Time, mostly. Every month a plant sits on the nursery it’s being watered, fed, weeded, spaced and handled — and the pot, the mix and the bench space all scale with it. Then there’s freight, the quiet cost on every big-grade order: a PB18 takes up 3-4 times the space of a 2.5L, and freight charges for space not for plants.

So when the PB18 costs several times the root trainer price, that’s not margin games. It’s two extra years of somebody’s mornings.

Where do orders go wrong?

Two ways, and they’re mirror images.

Paying for size the job doesn’t need — specifying 2.5L across a reveg block that root trainers would have covered, then losing the difference again on freight. And going too small for the deadline — root trainers planted late into drought, or in front of a client who expected a hedge by Christmas. The first mistake wastes money quietly. The second one wastes it publicly.

If you’re not sure, say what the job is — numbers, site, deadline — and let the grower talk you down a grade or up one. In my experience it’s more often down.

Right plant, right grade, right window. The plant doesn’t care what it cost — and given a fair start, the cheap one grows into the dear one soon enough.

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