this week’s radio slot I answered listeners’ questions on everything from a browning Thuja occidentalis ‘Smaragd’ to when to prune Lavatera, whether you can replant through seaweed mulch, how to coax flowers from a peace lily, protecting “geraniums” (pelargoniums) over winter, trimming a beech hedge, dealing with mushrooms in the lawn, and the best time to mulch rhubarb. We also touched on pollinator-friendly planting that’s transforming Irish towns.

You can listen back, here

Listener Questions & Answers

1) Thuja occidentalis ‘Smaragd’ going brown in a hedge

Problem: One tree has gone brown outside with some green inside, planted among 20 healthy trees, 5 ft apart, in for ~5 years.
My take: Unfortunately, it’s unlikely to recover and will probably die. The usual culprit is poor drainage/compaction causing root stress and secondary fungal issues. Thuja are shallow-rooted, so standing water around the root zone is fatal. Root damage from digging even 15–20 ft away can also trigger decline.
What you can try (low odds): Light, careful pruning; drench with copper sulphate in water; feed well (e.g. seaweed feed) to drive new growth. But expect to replace it and assess drainage before replanting.

2) Lavatera ‘Candyfloss’ (mallow) leggy in a pot – prune now?

Don’t prune now; it’s too cold. Wait until March–early April as temperatures rise.

Method: Gradual hard prune to encourage bushiness (e.g. take ~10% late March, then a bit more after 1–2 weeks).

Potting: Up-pot now to give roots room; plant out or pot on again next year.

Reality check: Lavatera are often short-lived, even with best care. Take summer cuttings next year for replacements.

3) “Summer stuff” not cut back — can I do it now?

If you mean herbaceous perennials, yes — you can cut back now (life has retreated to the roots). Or leave stems/seedheads for winter wildlife and tidy in March.
If you mean summer-flowering shrubs, leave pruning until spring.

4) Replanting through rain-rinsed seaweed in a re-dug bed

Generally yes for shrubs and spring bulbs; avoid very soft bedding like winter pansies/cyclamen right on fresh seaweed. Let seaweed weather in.

5) Peace lily (Spathiphyllum) not flowering after 4–5 years

Likely under-feeding / pot-bound. Repot and feed; I mentioned Bio Gold plant food as a solid option. If foliage is healthy and there’s no other stress, feeding should encourage blooms.

6) Do I need to bring “geraniums” in for winter?

If you mean bedding pelargoniums (what most of us call geraniums): yes, they’re frost-tender. Bring into a greenhouse/tunnel or cover with horticultural fleece on freezing nights.
True perennial geraniums (cranesbills) are herbaceous; they die back and can stay outside.

7) Beech hedge too wide — when to reduce?

Leave the hard reduction until early March next year.

8) Mushrooms/toadstools in the lawn — how to get rid?

They’re a natural response to conditions (often poor drainage) and the presence of fungi breaking down organic matter — part of a healthy soil web. They’ll disappear naturally soon. To truly prevent, you’d need to improve drainage and, in extreme cases, replace soil. I’d enjoy them while they last!

9) Is now the time to put manure on rhubarb? Horse vs farmyard?

Yes — winter is perfect for a manure mulch. Horse or farmyard are both grand. Also ideal around roses and many beds.

Pollinator-Friendly Planting (and why it makes us smile)

We gave a shout-out to councils and Tidy Towns groups moving from highly hybridised bedding to pollinator-friendly mixes. Waterford has led the way (those Dungarvan roundabouts!), and Cork is following suit — plantings that feed bees, look better for longer, and genuinely lift the spirits.

Quick Recap

Thuja ‘Smaragd’ browning: usually drainage/compaction; replace and improve site.

Lavatera: prune March–April, up-pot now; short-lived, take summer cuttings.

Perennials: cut back now or leave for wildlife; shrubs, wait till spring.

Seaweed mulch: fine for shrubs/bulbs; avoid soft bedding directly on it.

Peace lily: repot & feed to trigger flowering.

Pelargoniums: protect from frost; perennial geraniums can stay out.

Beech hedge: reshape early March.

Mushrooms: harmless; improve drainage if persistent.

Rhubarb: mulch with manure now.

Garden Design

Need personalised advice or a planting plan? Book an Online Garden Consultation with me and we’ll map out the next steps for your garden. Full details Here Garden Design Services Ireland - Expert Plans by Peter Dowdall – The Irish Gardener Store