The best hebes for New Zealand gardens (and the ones that sulk)

Quick answer: The most reliable hebes for New Zealand gardens are the small-leaved and whipcord types: Hebe albicans, Hebe sutherlandii, Hebe cupressioides, 'McEwanii', 'Red Edge' and 'Wiri Image'. Every one of them wants full sun and free-draining ground. Expect five to ten years of good looks before replacement, and heavy wet soil or deep shade will cut that short.

Late November, and there is one plant in the border the bumblebees will not leave alone. Violet spikes standing up off glossy green leaves, so thick with bees that the whole bush hums if you get your ear near it. Everything else is having a quiet week. The hebe is putting on a show.

Then you walk past the same plant four winters later and it is a grey ribcage with a bit of green on top.

That gap is why hebes get such a mixed report. They are the easiest native shrub in the country to fall for and one of the easiest to be disappointed by, and the difference nearly always comes down to which one you bought and where you put it.

Why do Hebes have such a short career?

Because they are short-lived shrubs, and that is not a fixable fault.

Five to ten years of good looks is a normal innings for a garden hebe. Some hold on to fifteen. Compared with a totara or a lacebark that is nothing, and it catches people out because a hebe at year two looks like it will be there forever.

Plan the bed around that number and it stops being a problem. Use hebes for the fast, flowering, filling-in layer, and put something with a longer life behind them for the structure. When the hebes start opening up at the base, they come out and new ones go in.

The other side of that coin is that hebes strike from cuttings more easily than almost anything else we grow. Half a dozen tips off your best plant in autumn gives you the replacements before you need them.

Which Hebes hold up best?

The small-leaved, grey-leaved and whipcord types. As a rough rule, the finer and tougher the leaf looks, the harder the plant is.

Hebe albicans. Blue-grey foliage in a tight dome to about 50cm, white flowers in early summer. It comes off South Island subalpine scrub above 1000m, and detached shoots of it have held through mid-winter at -10°C in testing. If you garden at Arrowtown or on a frosty inland terrace, this is the one to start with.

Hebe sutherlandii. A low mountain hebe with a spreading habit, roughly 30cm tall by 1m wide, rounded grey-green leaves, white flower spikes from spring right through to autumn. Frost hardy. Good over a wall or at the front of a dry bank where you want something flat and grey rather than another tussock.

Hebe cupressioides. The whipcord. Upright and rounded to about 2m, with tiny scale-like leaves clasping the stem so the whole plant reads more like a conifer than a hebe. Lilac flowers at the branch tips in early summer, and the grey form has foliage that smells of cedar when you brush it. It gives you evergreen structure without the clipping bill.

Hebe 'McEwanii'. A low spreading mound about 60cm each way. Narrow grey-green leaves stacked in neat rows along dark purple branchlets, pale lilac-blue flowers. Grey foliage for eleven months, flowers for the twelfth.

Hebe 'Red Edge'. Around 1m tall by 1.2m wide, grey leaves rimmed in red that deepens through winter, purple flowers. One of the two most-planted hebes in New Zealand, and deservedly so.

Hebe 'Wiri Image'. Glossy green, naturally rounded, mauve to violet flower spikes in quantity. About 1.2m tall and wide in an open sunny spot, tighter on dry or exposed ground. This is the one in the opening paragraph, the bumblebee magnet.

If you already know Wiri Mist and Veronica topiaria, they belong on this list too. I have left them short here because they get written about constantly and the six above do not.

At home, I have a border of Hebes around our patio area. On the side where the water runs off, none of them thrived, only a couple survived, so I ended up pulling them all up. On the drier edges, they absolutely love it – you’d think they were in different gardens.

Where do Hebes struggle?

Four situations, and none of them is about which variety you picked.

Shade. A hebe in heavy shade stretches for the light, opens up between the branches, and the inner leaves yellow and drop. You get a leggy plant that never flowers properly and never recovers its shape. Hebes are full-sun plants, and koromiko in particular will not wear shade at all.

Heavy, wet ground. This is the one that kills them outright. Hebes do not grow on clay or on soil that stays saturated. The planting hole fills with water, the roots run out of oxygen, phytophthora root rot moves in, and the plant dies slowly enough that people blame the weather. Around Dunedin and Mosgiel where the ground holds moisture and the sky stays grey for weeks, get them up on a mound or a bank rather than into a flat bed.

The salt front line. Hebes cope with coastal gardens fine as long as they are not being coated in spray. Constant salt on the foliage burns the leaves and eventually takes the plant out. The sheltered side of the house is fine; the seaward fence line is not.

Hard frost on the soft-leaved ones. The big broad-leaved species and the variegated cultivars are a different proposition to the alpine ones. A well-grown plant that has been through a winter takes moderate frost without complaint. A young one that went in three weeks ago on an exposed inland site has not earned that yet.

Which brings up the one genuine advantage of buying from down here. Our stock stands outside on the pad in Southland all winter, uncovered, no tunnels and no heat. So a hebe leaving us in spring has already met frost, wind and driving rain in its pot rather than coming out of a warm house soft and sappy. Up in Geraldine or across the plains, that plant is arriving over-prepared rather than under.

What actually kills a hebe that looked fine last month?

Downy mildew, usually. The pathogen is Peronospora grisea, and it is the single most common reason a healthy-looking hebe goes backwards fast.

What you see: a yellowish discolouration on the leaves, showing up on the lower leaves first and spreading across large parts of individual leaves. The leaves curl and distort. Turn one over and there is a fuzzy grey growth on the underside. Then those patches brown off and shrivel. A plant can be completely defoliated and killed.

It takes hold where plants are crowded together in damp shaded air. Full sun and space between plants make it rare. Overhead watering that leaves the foliage wet overnight makes it likely.

So the fix is nearly all cultural:

• Space them properly at planting and resist filling the gap with another one.

• Full sun.

• Water at the base, or water early enough in the day that the leaves dry off.

• Cut out affected leaves and stem sections as soon as you spot them; a plant caught early will come back.

• Keep the feeding up, because an underfed plant is a slower one to recover.

The other killer is the phytophthora in the wet-ground section above. Between them they account for most of the hebes that die before their time.

Can you cut a leggy hebe back hard?

Yes, and this is where hebes beat several of the popular hedging evergreens.

A hebe will generally sprout again when cut right back, down to about 10 to 15cm above ground level. Do it in spring or summer, with secateurs or a pruning saw, and do not go lower than 15cm. Try the same thing on a Griselinia or a Westringia that has gone bare at the base and you are gambling on what comes away.

Two conditions on that. The plant needs healthy shoots to start with, so a specimen already going backwards from mildew or root rot is not a candidate. And a hebe that has been sitting in shade may not have the reserves to re-establish after a hard cut.

Better than any of that is a light trim twice a year, early spring and late summer, taking a little each time. That keeps a hebe dense from the inside and pushes its useful life out by years.

Common questions

Are Hebes and Veronica the same plant?

Yes. Botanists moved the genus into Veronica, so you will see the same plant labelled Hebe cupressioides on one bench and Veronica cupressioides on the next. Nothing about the plant changed.

Do Hebes need feeding?

A light feed in spring when they start moving is plenty. Rich soil and heavy feeding produce soft, lax, leggy growth, which is the opposite of what you want from a hebe.

How far apart do you plant a hebe hedge?

Half the height you intend to hold the hedge at. So a hedge kept at 600mm goes in at 300mm centres, and one kept at 1m goes in at 500mm. That is our rule for every species. Published hebe hedge spacing is usually quoted around 40 to 45cm regardless of finished height, which will be too tight for anything you plan to hold above a metre.

Will hebes grow under trees?

Not well. Shade is the fastest way to a stretched, mildewed, disappointing hebe. If the spot only gets a couple of hours of sun, plant something that wants those conditions instead.

Can I take my own cuttings?

Easily. Hebes are among the simplest natives to strike, and a handful of semi-hardwood tips taken in autumn will give you replacements for the plants that are on their way out.

Hebes are a five to ten year plant that will out-flower anything else in the border for those years, provided you give them sun and drainage and take the secateurs to them twice a season. Buy them for what they are, and they are hard to beat.

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