I have a Japanese box hedge which is not exactly dying, but is definitely failing to thrive. When I moved in (5 years ago) it was looking much better. So it's not about the location, but that the previous owner knows something I do not.

It is on the north side of the house and receives plenty of sun. I have used sugar-cane mulch to keep weeds to a minimum. Nearby roses are fertilized with chook manure and commercial rose food. The roses are growing well as is nearby murraya hedge.

Over the last 6 months I have tried a few different things:

  • fertilizing with blood and bone,
  • fertilizing with cow manure,
  • spraying with a fortnightly mixture of Seasol and Powerfeed.

There have been periods of steady rainfall for weeks which have not seemed to help.

Do I need to test the soil? Treat for pests?

I took a couple of pictures so you can see what I mean.

Some observations:-

  • on the shady side, there is a green tinge to the bark
  • leaves appear to be yellowing from the tips first and then going brown
  • some unhealthy looking leaves have small brown dots along the edge of the leaf, more prominent on the top of the leaf than the bottom
  • cross-section the root does not appear to have a blue tinge (my mobile phone camera is not too good a close-ups)
  • the soil looks good (noticed few worms when I dug this up). Soil is clayey

Japanese box hedge Japanese box hedge Japenese box hedge extracted Japenese box hedge root cross-section

  • It's almost time for me to hit the hay & catch a few ZZZ's, but before doing so I'll leave you with this: mobot.org/gardeninghelp/plantfinder/… -- to have a browse through (if you have the time). – Mike Perry Jul 16 '11 at 6:34
  • @WW01, Are the roots a blue-black colour in cross section? – Mancuniensis Jul 16 '11 at 13:58
  • 1
    @Mancuniensis: Not sure I'll have a look when it's light. The last plant on one end is basically dead so I'll pull it out and inspect. – WW01 Jul 17 '11 at 11:23
  • WW01, What's Wrong with My Boxwood? web.extension.illinois.edu/podcasts/gc/201105_827.html -- Please note, it does not directly answer your question, but I believe it will give you some things to consider, best cause of action... – Mike Perry Jul 19 '11 at 19:44
  • WW01: If you could examine a root cross-section of one that is still alive but yellowing badly and becoming defoliated, and tell us what color it is, this would make it easier to diagnose the problem. Thanks. – Mancuniensis Jul 21 '11 at 10:52
up vote 6 down vote accepted

This is exactly what I suspected when I asked you to examine a cross-section of the roots, given that you have had a prolonged period of rainfall. In addition to giving the shrubs collar rot, when there is heavy rain the mulch is probably causing the soil to become waterlogged, particularly if your soil is clayey and not very free-draining.

General yellowing of foliage may be symptomatic of waterlogging, especially on heavy clay soils. Roots subjected to waterlogging are usually a blue-black colour in cross section and fall apart when teased out. Damaged roots should be removed, top growth trimmed back and the box replanted.

Box/ Royal Horticultural Society

Judging from your photo, I don't think the roots of your box shrubs have reached this stage yet; however, I would remove the mulch completely and, once the plants begin to recover, next spring, apply a good general fertilizer such as Grow More (2oz per square yard), as suggested in the RHS article. I would definitely avoid using cow manure, as it tends to make clay soils heavier still and even less free-draining; well-rotted horse manure, on the other hand, is very good at opening up the pore structure of heavy soils, which improves drainage and aeration.

I took the plant I dug up into a gardening shop. They examined it and believe that there is damage around the top of the roots/bottom of the stem due to too much mulch too close to the plant.

I've removed the mulch from the base of the plants and will see if they improve.

Give the plants a good dose of monoammonium phosphate (or MAP), around a handful per plant (spread across the row - not piled!). It's easily found in hardware or farm supply stores.

This will provide Nitrogen for the leaves and a shot of Phosphorus to develop new roots.

I had a very similar problem with my Japanese box plants. What I did is:

  • completely remove all the mulch.
  • add some Monoammonium Phosphate (MAP) fertilizer, and
  • check the soil every other day, checking for the moisture content, not too dry, nor too wet.

I'm not a gardener but these tricks fixed my problem. Now my plants are beautiful.

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