Q My mother has recently moved to a property, which did once have a nice garden, but it’s rather overgrown now. In one corner there are some nice cabbage trees, but they’re surrounded with a mass of fern and ivy growing among rocks, and heaven knows what else is under the ivy. We’ve tried pulling it out, but it was too hard. There are also some big clumps of agapanthus we want to get rid of. What do you suggest?
Question from J. Elliott, Whakatane
A The fern in your photo looks like tuber ladder fern, Nephrolepis cordifolia, which is almost impossible to clear out by hand. It spreads by long, creeping runners just below the soil surface, enabling it to quickly form large patches, and, to make matters worse, it produces small tubers, which, if left in the soil, quickly grow into new plants. As a further means of reproduction it produces spores that drift far and wide in the wind, so it’s a weed that crops up in many warm parts of the country. Like your other two problem plants, ivy and agapanthus, it was first introduced as a desirable ornamental plant, but has ‘escaped’ from gardens and is now considered a pest.
There are much better-behaved species of Nephrolepis that make attractive garden plants and are not weedy, including our relatively rare native N. flexuosa, which does not have tubers, and of course there’s the Boston fern, often sold as an indoor plant, which is also a Nephrolepis.
The only way to get good control of tuber ladder fern in a situation like yours is careful spraying. Some herbicides only knock it back for a while then the tubers sprout again, but I know from experience that spraying it with a mix of glyphosate and Escort (which contains the active ingredient metsulfuron methyl) should do the job reasonably well. Glyphosate also works quite well on ivy so I’d apply the spray mix to both these weeds. You can buy Escort in most garden centres; it seems quite expensive for the small container you get, but a little goes a long way. It comes as granules with a lid you use to measure it out. Make a mix of two grams of Escort plus 100ml of glyphosate, in five litres of water. Dissolve the Escort granules in water before adding the glyphosate. Add a sticker/spreader, such as Pulse, at the rate recommended on the label, this helps ensure the spray spreads evenly over and penetrates the leaves efficiently, for maximum effect. Be careful as you spray, make sure to get good coverage over the weeds, but not on to nearby desirable plants. It will take several weeks for the fern and ivy to die off and you may have to spot spray again to get any you missed the first time, which is quite common with a dense patch of weeds especially with ivy, where foliage deep in the pile of vegetation may not get hit with the first spray application.
You can always try digging out agapanthus, but it can be back-breaking work with large clumps. I reckon the easiest way is to use a pruning saw or machete to cut them off close to the ground then apply a layer of Vigilant Gel or Cut’n’Paste MetGel to the exposed end of the cut rhizome.
Answer by Andrew Maloy (The Plant Doctor)