By Dauvminer
United Kingdom 
Sir/Madam, Several years ago I planted 30 Leylandi conifers. Two years ago I killed them by cutting of all of the side limbs and beheading them at two metres tall. I left the stripped trunks insitu to support six-feet high deer fencing. Since then I have planted an assortment of different shrubs between the dead trunks - and every one of them has died-of within 5 to 10 days. My question is: - Does the decaying roots of dead conifers produce a residue in the surrounding soil strong enough to kill-of new young shrubs?
David Morris.
29 Sep, 2015
Answers
Dear Sir,
Many thanks for your illuminating answer!
There simply had to be a reason for the demise of my new shrubs.
You have given me much food for thought (not a pun!) and I shall heed your advice.
D. M. M.
30 Sep, 2015
Bamboo is in fact a lady and this is a very informal site so no need for dear sir etc :o)
I agree with Bamboo that it sounds more likely to be lack of water and nutrients in the soil. However were the roots of the plants you planted in good condition? And did you water them every day when you planted them.
Another thought the soil will be on the acidic side due to the conifer leaf drop over the years. were the plants suitable for an acid soil? Some plants cant tolerate acid ,some aren't bothered and some cant tolerate lime/alkaline soils.
what shrubs did you plant?
1 Oct, 2015
Lady?!! Anyone who knows me would be falling about laughing, like I am right now, I'm afraid I'm not at all ladylike Seaburngirl;-))) I'm just a person who happens to be biologically female...
1 Oct, 2015
lady not a laydee :p. female if you prefer but I bet you do scrub up well :o)
2 Oct, 2015
Once upon a time, yes, I did scrub up well, but really, not so much now...! Getting old...
2 Oct, 2015
The problem won't be allelopathic in origin, meaning they don't produce a toxin to ward off other plants, but is more likely to be that, as you planted the trees 'several' years ago, but only killed them off two years ago, the soil is full of root material and impoverished from a nutritional point of view, probably also being pretty dry. The only other possibility is that honey fungus is present, which does appear in relation to dead trunks and roots in the garden, and that might well mean most plants won't grow there. Even so, everything dying within ten days of being planted is too fast for honey fungus to be cause.
You might be able to repeat the planting inbetween the dead trunks, but I suggest you dig thoroughly all around the trunks and incorporate composted manure or something similar, let it settle, then try planting. You will need to keep whatever you do plant well watered. The best solution really is to have the trunks and roots removed - you do run the risk of honey fungus developing if they are left to rot down naturally.
29 Sep, 2015