URBAN FARMER:Your soil will really dig being cared for in order to nurture healthy plants next season, writes FIONNUALA FLANAGAN

THE FIRST TIME I heard the expression “green manure” was some years ago, while on a visit to the Organic Centre in Rossinver, Co Leitrim, as I admired the pretty blue flowers and ferny foliage of Phacelia tanacetifolia growing en masse in the vegetable beds.

It was then gently explained to me that this free-flowering annual plant wasn’t there to be ‘pretty’, but rather to be used as a fast-growing green manure while the ground was empty of vegetables.

When in active growth, its dense root system would help improve the soil structure while the dense canopy of leaves would temporarily suppress weed growth. Later, the entire crop would be dug or rotovated into the soil, where its leaves would quickly rot down to provide a quick release of nitrogen and other nutrients.

Since then, while I still admire the lacy blue blossoms of this graceful annual plant (and I still think it’s pretty), I now know it as a versatile green manure crop that’s much valued by organic gardeners.

Phacelia is just one of a range of both annual and perennial plants used in this way, some of which are grown as short-term ‘catch crops’ in spring and summer while others are sown in autumn as overwintering crops to be dug in the following spring. All are useful, multipurpose green manures that improve the soil’s structure, fertility and drought-resistance while many are also attractive to bees and other beneficial insects.

In the OPW’s walled kitchen garden, gardeners Meeda Downey and Brian Quinn planted their first green manure of rye grass this time last year, and are delighted with the results.

“We sowed seed last autumn and then left the crop in the ground until mid-spring,” explains Brian. “In March of this year, we strimmed the crop down to the ground before rotovating it into the soil.

“We decided to rotovate the patch twice more over the following six weeks, to make sure that it was completely dug in and rotted down, before we planted sweet corn in early summer. We noticed a massive improvement in the soil structure almost immediately, it was lovely and crumbly. We were really impressed.”

So impressed, in fact, that Meeda and Brian have decided to sow a variety of green manures this autumn, including an overwintering mix of winter vetch, crimson clover and Italian ryegrass which they’ve sourced from Fruithill Organic Farm in Co Cork.

Having just recently cleared the vegetable beds where the potatoes, sweetcorn, sunflowers and sweet pea grew, last week the gardeners removed any perennial weeds by hand, before then rotovating and raking the plots in preparation for sowing.

Making sure, as the OPW gardeners did, that the soil is clear of persistent perennial weeds, is an important rule as regards preparing your vegetable patch for a crop of green manure.

“You’ve got to make sure that you’ve dug out the roots of weeds like bindweed, dock, buttercup, dandelion or scutch before sowing seed, because you don’t want these to re-appear in the ground in the months to come,” explains Brian. “And if you’re using a rotovator, hand-pick any large stones also.”

Try also to avoid working/digging the soil in wet weather, which can cause problems with compaction and panning. “It helped a lot that we had that great dry spell of weather,” says Meeda, “as we couldn’t have used the rotovator (they use a Valpadana Blitz 70) in wet weather – it would have done way too much damage to the soil.”

After thoroughly preparing the ground, the OPW gardeners then broadcast the seed of green manure by hand, using a little bit more than the recommended rates.

“We raked it in lightly before spreading a little bit extra for the birds and squirrels,” adds Meeda, explaining that the crows, blackbirds and magpies made frequent raids on the newly sown seed last autumn, which affected the evenness of the crop’s germination.

“There were bare patches where they’d stolen a lot of the seed and, months later, we were still finding little clusters of rye germinating in odd places all over the garden, where the squirrels had hoarded it away,” she explains. “So this year, we’ve decided to factor that in when it comes to calculating how many kilos of seed we need to spread. That way, the birds and squirrels get their share and we still get a good crop of green manure.”

Alternatively, those urban farmers with smaller vegetable patches can net their newly sown crop of green manure until it’s successfully germinated.

Urban farmers who plan on sowing green manure this autumn will need to be quick, however, as even the hardiest types should be sown outdoors by the end of October/beginning of November (order from Fruithill Farm’s website – fruithillfarm.com – or phone 027-50710).

You can also sow your green manure under cover in a glasshouse/polytunnel, where it’s great for tired, overused soil. Alternatively, wait until next spring when you can sow the spring/summer types, which include many of the nitrogen-fixing plants such as summer vetch, sweet lupin and clovers.

Speaking of being quick, another job for the time-pressed urban farmer to keep in mind is the planting of spring cabbage, which also needs to go into the ground by the end of this month.

And if you forgot or didn’t get the chance to grow your own young spring cabbage plants from seed earlier this summer, be reassured that you can still buy young plants from your local garden centre.

Plant these now in a sunny, sheltered spot in your vegetable patch, but disturb the soil as little as possible while doing so, as all members of the cabbage family dislike both freshly dug ground and/or freshly spread manure.

Spring cabbage, just like the summer, autumn and hardy winter types, also does best in a non-acid soil, so lime it if necessary (you should aim for a pH of roughly 6.5-7.5).

Use a dibber to plant in lines 30cm apart, with 30cm between plants. Alternatively, leave only 10cm between plants, but remove two out of every three plants in early spring and use as spring greens.

Plant quite deeply, so that the bottom set of leaves are just above ground level, water if necessary and then gently tread down the soil to prevent plants from being loosened by winter storms.

A sprinkle of the organic-friendly slug-pellet, Ferramol, after planting should prevent the leaves from being damaged or eaten.

OPW gardeners Brian and Meeda also advise using protective discs, made out of a weed-suppressant fabric such as Mypex, which should be placed around the base of each stem – cut a radial slit in each disc to help them fit snugly. These will help prevent an attack of cabbage root-fly, the larvae of which can kill young plants or slow the growth of more mature crops.

“Earth-up the young plants a few weeks after planting to prevent them being lifted by frosts, and then keep an eye out for weeds. And remember, as with all brassicas, you have to rotate the crops each year,” warns Meeda. “Otherwise you’ll get a build-up of diseases and pests in the soil.”

Which is the point at which I’ll admit, like many other urban farmers, to getting a mite confused, for I’ve never quite understood how crop rotation works when it comes to cabbages. For example, do I plant the spring cabbages away from where the summer cabbages were, or do they go together? And what about the autumn cabbages? And the hardy winter types? And next year’s summer cabbages?

Hmmm, who would have thought that it could all get quite so complicated . . .

We featured the wrong Sow and Plant panel last week

The OPW’s Victorian walled kitchen garden is in the grounds of the Phoenix Park Visitor Centre, beside the Phoenix Park Cafe and Ashtown Castle. The gardens are open daily from 10am to 4.30pm

Next week Urban Farmer in Property will cover the pumpkin harvest and growing kale for Halloween colcannon

Fionnuala Fallon is a garden designer and writer