Thorny problems: the green invader

imageHelen Yemm answers your questions on liverwort, yellow geranium and more.

Low-spreading liverwort

My garden has recently become infested with a very low-spreading green invader. I don’t think it is helxine (Soleirolia soleirolii), aka mind-your-own-business, as mine doesn’t look tufty or like anything you would want growing in your house. It seems to hold the same territory as moss, and I have therefore been working hard to improve the soil with loads of home-made compost. Have you any ideas or words of comfort?

Trina Golland, Hatfield

Without a picture I can’t be certain, but this is very probably a liverwort of some kind. Primitive “plants”, liverworts, algae and the moss that you mention are often lumped together in a single category because they inhabit and infest the same territory – damp and compacted soil that is winter-shady, slightly impoverished and, in many cases, slightly acid. None of them actually kills the plants they infest, but they all look unsightly and can inhibit seedling growth, smother small alpines on rockeries and so on.

As for identification: most of us, at some point, will have bought from a nursery an aged plant with flat, overlapping dark green scale-like “leaves” infesting the top of the pot: that’s liverwort.

Eradication of liverwort is difficult if your garden soil provides ideal conditions for its establishment. Physical removal of the shallow, rootless growth is helpful, and you should also regularly hoe the top inch or two of soil to keep the surface of your beds “disturbed”. Where appropriate (where it is growing in isolation, away from other greenery), liverwort can be treated with a glyphosate weed killer, but you have to add a dash of washing-up liquid to the solution so that it clings to the scales and doesn’t just run off.

Relieving soil compaction is important and you have been regularly adding compost to your garden soil, you say, which is great. But I think you would do well to dig an equal quantity of fine grit or coarse sand into your borders in order to improve the drainage. Deep organic surface mulches (bark chippings and such) also help to smother liverwort around established plants, which should be regularly fed. But, basically, it is a case of just keeping at it.

Yellow pelargoniums

Three years ago I bought plug plants of a newly arrived yellow geranium (pelargonium). I keep them indoors all year round in a frost-free conservatory. They have thrived but never flowered. Have you any suggestions as to how I may persuade them to do so?

Anonymous Telegraph subscriber, Liverpool

I was similarly seduced by the idea of a “yellow” geranium a couple of years ago and bought a young plant that had a single budded flower stem. Knowing from past experience that descriptions from plant breeders and suppliers can be, how shall I put it, a little colourful, it was still with great anticipation that I waited for the flowers to open.

As I half expected, they were less “yellow” and more of a lovely dull cream. I potted my plant on and put it outside for the summer in close proximity to a lime green helichrysum and a dark-flowered, trailing Pelargonium ‘Tomcat’, and waited for an entangled colour fest. However, the yellow geranium barely flowered again, although after overwintering it (like yours, in a cool conservatory), it did better the following year.

So, based on personal experience, several points that may help you spring to mind. I would put your pelargoniums outside in the summer (from late May, after a period of acclimatisation) in as sunny a position as you can find. Choice of compost may make a difference. Although almost always sold in pots of multi-purpose compost, they actually prefer quite tough root conditions. I use loam-based John Innes No. 3 with a tiny bit of home-made compost or multi-purpose mixed in. I go easy on the watering, too.

Finally, we are seldom told this for obvious reasons, but “special” pelargoniums like these yellow ones are frequently a bit shy to flower, even when mature. However, once my own plant was fully mature, liquid feeding with tomato food (or something high in potash, specifically aimed at flowering annuals) did seem to make a difference. In a nutshell: don’t give up yet.

Overstuffed raised beds

We have a small vegetable patch and grow broad and runner beans, spinach and some soft fruit. We add home-made compost every year and we crop-rotate a little where we can. The soil is pH neutral. The slightly raised beds are overflowing with good textured soil/compost, but every year the yields get smaller. We are not sure what to do next. Your advice would be appreciated.

Val Kelly, via email

There are two courses of action open to you, either of which should add a little vim and vigour to your crops. You say your beds are “slightly raised”. You could simply raise them further by replacing or adding to the timber edges, or you could instead remove some of the existing soil. Since it is perfectly good stuff and presumably fine and weed-free, mixed with equal quantities of sharp sand it will be a good top dressing for your lawn, or as an addition to condition the soil in your flower beds. Whichever you choose, you could then simply add well-rotted animal manure to the soil in the vegetable beds – ringing the changes this year from your usual addition of home-made compost. Application of chicken manure pellets also peps up the soil fertility a bit, I have found.

I know I am going off on a tangent, and I appreciate that this is not how you got to where you are with your raised beds, but it always alarms me slightly when I hear about people installing new beds and promptly filling them to the absolute brim with soil and compost. It takes time for the penny to drop: that the process of annually adding quantities of muck and/or garden compost – the whole big thing about growing vegetables in raised beds – is bound to lead to a surfeit of the stuff. After a few years you have to actually start taking soil out before you can fit more muck in.

Leek lament

The vile leek moth is moving ever northwards. Richard Matkin from Burton upon Trent is the latest reader to wring his hands over this dreadful pest, the larvae of which can spoil leek (and related onion and garlic) crops by tunnelling into stems and bulbs. He fears (and he is quite right) that nothing he can spray or water on his leeks will kill off this seemingly insignificant little moth, which created havoc last year. The only thing he (and others) can do is grow their crops under horticultural fleece or ultra-fine Enviromesh (both available from garden centres). There are two generations of moths each year – one in May/June, and another (worse one) in August.

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