Using a brushcutter with a blade head attachment can be a powerful way to manage thick, fibrous vegetation in your garden. However, not all plants respond equally to this type of vigorous pruning. To keep your garden thriving, it’s essential to understand not only the type of plant you’re cutting back but also the specific needs and growth behaviours of each species or cultivar within a genus. This article will guide you through the principles of plant pruning using a brushcutter, with a focus on strappy-leafed plants like Lomandra, Dianella, and Liriope, and highlight precautions for avoiding damage to plants like Phormium.

Pruning Baby Breeze™ Dianella hard with an extension hedge trimmer. (Cultivar currently not available in NZ)

Why Prune Strappy Plants At All?

I’m not one to advise for dome pruning to keep strappy plants ‘neat and tidy’ – this can reduce the plant’s ability to photosynthesise while crowding out new growth over time. It also limits airflow, favouring diseases and pests.

However, a hard prune every few years gives a strappy plant a chance to start fresh. It can shed its old, damaged and dead foliage which can be removed as green waste, or even better, chopped and dropped as mulch.

Alternatives to hard pruning can be time-consuming, but well worth doing for high impact feature plants, especially where the project budget allows. You can hand-remove older, dead foliage if it comes off, as in the case of agapanthus, or you may be better off pruning dead foliage with a pair of secateurs at the leaf’s base on the stem.

Deadheading flower stalks at the base is a normal part of maintaining strappies like dianellas and agapanthus. You can also deadhead lomandras and liriopes, though this isn’t usually done due to time constraints.

Which Tools to Use

Hedge trimmers are a great tool for cutting strappy plants, because they make cleaner cuts when they’re properly maintained with sharp flush blades. Brushcutters can tear leaves rather than cutting them, and the leaves can become wrapped around the spinning head.

Mowers can be great, but again, the leaves can wrap around the spinning blades and cause headaches as you try to remove them. Brushcutters with plastic cord are great for softer plants, but firmer fibrous leaves can tear instead of cutting – try using a metal blade head attachment instead.

Isabella™ Liriope getting a hard prune with a mower. (Cultivar currently not available in NZ)

The Importance of Species-Specific Care

While it might be tempting to take a one-size-fits-all approach to pruning, plants within the same genus can behave very differently when cut back. Depending on the species or even the cultivar, some plants respond well to hard pruning, while others may decline if their growth points are damaged. To preserve the health and aesthetics of your plants, pay close attention to their individual needs.

Experimenting with cutting a single stem or rhizome within a clump and observing its growth response over a couple of warm months is a way to test your plant’s ability to tolerate hard cuts.

For instance, some varieties of Lomandra and Dianella will tolerate or even benefit from severe cutting through their stems to rejuvenate the plant. Such plants are easily able to regrow new shoots from ‘epicormic’ (dormant) buds on bare stems.

On the other hand, certain cultivars prefer more conservative pruning that avoids damage to their apical growing tip because they are less capable of regrowing from epicormic buds.

Baby Breeze™ Dianella can take a very hard cut.

Understanding the Apical Growing Tip

While I can’t find any sources to back up the claim I’m about to make, it’s a claim based on observations I’ve made from over a decade in landscape maintenance matched with my formal horticultural education (Diploma of Horticulture from Australia). I’ve asked a few clever colleagues and experts in my network and they all said that I could be right about this.

I believe a strappy plant’s ability to bounce back from a hard prune depends on its ability to recover from having the apical tips removed and their ability to regrow easily from lateral buds.

The apical growing tip is the primary growth point at the centre of each fan of foliage on each individual stem (called a ‘rosette’). It produces new leaves upwardly which eventually die off to reveal uncovered stems as the plant ages, driving the upward growth of the plant.

For strappy-leafed plants like Dianella and Lomandra, this tip can be found nestled in the centre of each rosette where the fresh leaves fan out from a central point. With lomandras in particular, there may be many stems closely packed and so the apical tips may not be immediately visible, but if you have a feel around, you may be able to find the lowest point of least resistance.

Damaging this growing point can lead to lacklustre growth responses or even the death of the plant. Instead, aim to trim just above this point or remove older foliage around it to allow for fresh, healthy growth.

If you’re unsure, tread on the side of caution. Watch the growth response and amend your approach accordingly next hard cut. You may even choose to amend your pruning sooner rather than later if you feel you should have gone harder.

Finding the apical tip in strappy plants:

• Look for the newest, tender leaves emerging from the inside of each rosette, each emerging from an individual stem within the clump.
• Avoid cutting too close to this area if you’re unsure about the species’ tolerance to hard pruning.
• Watch the growth response. If you think it wants a harder cut after a couple of months, consider cutting a bit harder next time.

Our head breeder, Todd Layt, believes that most strappy plants can recover from pruning 10cm from the ground. This would be in line with my claim regarding apical tips, as there should be a number of apical tips below 10cm within a clump.

Notice the individual stems, each with an apical growing tip. The hardest cuts are made beyond the apical growing tip, while the less drastic cuts preserve the apical growing tips. Baby Breeze™ Dianella is currently unavailable in NZ.

Recommended Hackable Plants

Some plants are better suited to being cut back with a hedge trimmer or brushcutter with a blade head, making them great candidates for low-maintenance gardeners.

Keeping in mind that individual species and cultivated varieties each have their own preferred pruning heights, here are three genera that tend to appreciate a good, had cut-back:

1. Lomandra

These hardy, tufted grass-like plants often respond well to a hard cut into the foliage, and clearing out older, damaged leaves. https://ozbreed.co.nz/plant-ranges/strappy-leaf-plants/#lomandra

Tanika™ Lomandra longifolia ‘LM300’ PVR. https://ozbreed.co.nz/plant-ranges/strappy-leaf-plants/tanika-lomandra/

2. Dianella

Commonly known as flax lilies, Dianella is another robust genus well-suited to blade cutting. https://ozbreed.co.nz/plant-ranges/strappy-leaf-plants/#dianella

Emerald Arch™ Dianella tasmanica ‘DT23’. http://ozbreed.co.nz/plant-ranges/strappy-leaf-plants/emerald-arch-dianella/

3. Liriope

Known for their drought tolerance and attractive clumps of strap-like leaves, Liriope plants often respond well to hard cutting. https://ozbreed.co.nz/plant-ranges/strappy-leaf-plants/#liriope

Amethyst™ Liriope muscari. http://ozbreed.co.nz/plant-ranges/strappy-leaf-plants/amethyst-liriope-muscari/

True Grasses

True grasses may look like other strappy plants such as Lomandra and Dianella, but they aren’t closely related at all. They’re distinguished by their stalks (stems) with knobby knees (nodes).

Clumping grasses like Australian Pennisetum, Poa and Themeda tend to sacrifice older growth in favour of new growth each year. If they’re left unpruned, new stalks will need to compete for sunlight with the unproductive dead stems from previous years, while also being smothered which can encourage pests and diseases.

Nature has a couple of solutions for this. Herbivores will often graze clumping grasses down, and (controlled) fire can also give the plants a fresh start by removing older foliage without damaging the roots.

I’m not irresponsible enough to recommend anybody reading this to burn their grasses, however there are contractors that offer this service. Contact your local fire authorities for more info. Or, you could simply brushcut or hedge prune them down to the base just before spring each year to get the most out of your grasses.

Nafray® Cenchrus is a native Australian fountain grass (unfortunately unavailable in NZ)

Plants to Handle With Care: Phormium

Unlike the genera mentioned above, Phormium—commonly known as New Zealand flax—rarely responds well to hard pruning. When managing Phormium, I have had success pruning to remove dead or damaged leaves at the base, cutting them back to the stem without disturbing healthy foliage.

Brushcutter Best Practices

• Ensure the blade is sharp and suited for cutting through tough plant material.
• Wear appropriate safety gear, including gloves, goggles, and sturdy boots.
• Position the blade so that you cut through the foliage with smooth, deliberate motions.
• Feel around for a technique that minimises the strappy leaves wrapping around the head.
• You’ll need to regularly turn the machine off and unwrap straps that get caught around the head. (Hedge trimmers don’t do this)
• Take care not to dig into the ground or cut into the crown of the plant, as this can cause damage to the machine.

Hedge Trimmer Best Practices

• Keep your blades sharp and flush together – blades that don’t meet together tend to rip foliage instead of cleanly cutting.
• Wear appropriate safety gear, including gloves, goggles, and sturdy boots.
• Position the blade so that you cut through the foliage with smooth, deliberate motions.
• In a perfect world, you’d take care not to dig into the ground or cut into the crown of the plant, as this can cause machine damage.
• Start at the base of the plant and work up, taking care to cut every single leaf.
• If you’re raking the waste, go back over everything with a second round of pruning to find the leaves you missed.

Final Thoughts

Thoughtful consideration of each plant’s species, growth patterns, and tolerance for cutting is fundamental for successful results. When in doubt, cut conservatively, avoiding damage to the apical growing tip, and watch the growth response to see if there are any improvements you can make to your approach next time.

Prioritise planting species and varieties known to bounce back after pruning, especially plants like Lomandra, Dianella, and Liriope. Browse some of Ozbreed’s strappy plants in the genera Lomandra , Dianella and Liriope , and prune them just hard enough to promote a healthy, thriving growth response.