Hedge gap in-filling by underplanting - Six on Saturday

Since we removed our old greenhouse, we've exposed a four-metre length of the old hawthorn hedge at the northern boundary.

Although it has quite healthy upper growth and is still making good shows of blossom and berries, this hedge is very old and spans the length of the boundary which we took over when we bought the slice of additional land to the west to extend our garden.

Amateurish attempts have been made in the past to 'lay' the hedge by partially cutting through some of the trunks and bending them over to the horizontal so they maintain a growing connection with the tree, but then sprout more upward branches to fill in the lower areas. 

However, what with this poor quality laying and the lower part of the hedge being shaded by our old greenhouse for seven years, the base of the hawthorn hedge is very open and provides little or no low-level cover and wind protection to the garden now that the greenhouse has gone.  

And hawthorn is deciduous, so it will be even worse during the winter months when there are no leaves on the upper branches.

large gaps lowdown in the hedge behind the retaining wall
(photo taken before we moved the fig tree here)

Although winds from the north are not too common here, when they do arrive they're usually strong and very cold, so we thought we'd try to fill the lower gaps to protect the garden, and with a longer-term view of creating a full-height evergreen screen.


To do this, we've underplanted very young pyracanthas in amongst the established roots of the old hawthorn hedge.   

You might think they haven't any chance of growing properly in this location given that they need to compete with the well-established hawthorn roots for water and nutrients, but we have experience of this infill process from our earlier efforts on the eastern section of the same length of hedge.

Around four years ago, we planted seven young pyracanthas in between the hawthorn roots of this eastern section, and for the same reason, i.e. to thicken the lower part of the boundary and also to make an evergreen windbreak and privacy screen.   

This has been very successful, and we now have 1.5m high pyracanthas that form an integral part of the hedge screen.   As they grow upwards and also thicken out, we're progressively undercutting the south-facing hawthorn branches all the way back to their trunks to create additonal space for the pyracanthas to grow into.  

now behind the new greenhouse ...

In this way, we hope eventually to create a 'composite' hedge, with the side facing into our garden showing almost all evergreen pyracantha and the outside being predominantly deciduous hawthorn.

This eastern section of hedge is now behind the new greenhouse, but it shouldn't suffer too much since the rear of the new greenhouse is fully glazed and therefore there's still plenty of light that can reach the lower branches.

And early last spring, we planted another two small pyracanthas slightly to the west of the more established ones to extend the infilled length, and these too have also started to fill out.  At the same time, we'd covered the whole area behind the old greenhouse with a weed membrane and a gravel topping just to keep the weeds under control.

We'd first laid pressure-treated boards along the base of the posts that support the farmer's wire stock fencing, to keep all the gravel on our side of the fence.

behind the old greenhouse early last year, 
with the gravel retaining boards at the fenceline

In previous years, it was like a jungle behind there each July.  Until we'd suppressed the nettles, brambles and other weeds with the membrane, it was a dreaded once-a-year job to get in behind the old greenhouse and pull them all out, very awkward due to the restricted access and the presence of very sharp hawthorn branches !

But access to get in and carry out the new additional underplanting works is no problem now the old greenhouse has gone.

So this time around, I bought six more very small pyracantha saplings, and made planting holes through the weed membrane, locating suitable gaps between the hawthorn roots.  I locally cleared the gravel mulch out of the way, and then cut through the membrane with a knife before peeling it back to expose the ground beneath.


I made the planting holes as large as possible and replaced the soil with a mix of fresh topsoil and compost, and then planted the new saplings.  I managed to find five suitable locations between roots to place the pyracanthas.    The sixth sapling was potted on as a future spare.

three very small pyracanthas, nothing much to see at the minute ...

last year's plantings in the foreground, two new
pyracanthas tucked away further back ...

At the extreme end of the hedgerow, at the corner with the western boundary, I'd initially planted out a Choisya ternata 'Brica' shrub which had been growing in the garden in a container for many years.   But after only a few weeks, I'd replaced this with a Mahonia x media 'Charity' shrub - the Choisya went back into its container.  

the Choisya ....

... and now the Mahonia ...

I'd originally wanted a Mahonia in that corner, for its winter flowers, but the garden centres were closed at the time and I don't like the idea of buying large, expensive plants on-line.   I order small plants on-line all the time, but for larger specimens I like to see what I'm buying.   Anyway, the garden centres have since re-opened, and I managed to find a 750 mm high Mahonia. 

And the Mahonia has very sharp spikes on its leaves, and so it's better to be tucked well away in that corner out of harm's way.

It seems that the trick with infilling old hedges by underplanting in this way is to plant very small saplings, and to spot water & feed them regularly in their early days so they always get first crack at the available moisture and fertiliser. 

In this way, they seem to become well-established after a few years and are then more than capable of holding their own against the competition from the old hawthorn roots.

However, it might take many more years after that time to form a dense evergreen screen and effective windbreak, so we may also add a temporary willow or bamboo screen at the fenceline before the onset of next winter.

Head over to the host of Six on Saturday, The Propagator, for more garden inspiration from around the world.