Oca, Oxalis tuberosa

Jeremy Bartlett's LET IT GROW blog Posted on by
Oca tubers

A bucket full of Oca tubers

Yesterday I lifted my crop of Oca tubers from the allotment: a good harvest of tubers, nearly a bucket full, weighing a stone (14lb or 6.35kg), from twelve plants.

I started off with just five tubers in spring 2014. I was sent these because I was taking part in a Garden Organic Members’ Experiment, a trial of growing Oca in this country. This time last year I harvested about 1lb (2.1kg) of tubers and I ate some of these and saved the rest to start off this year’s plants. I plan to do the same thing with this year’s crop and gradually increase the amount of Oca I grow.

Oca is Oxalis tuberosa, sometimes known as the New Zealand Yam. (It was introduced into New Zealand in the 1860s.) It is a member of the Wood Sorrel family, the Oxalidaceae. It comes from the central and southern Andes, from Venezuela south to Argentina, where it is grown for its root tubers. In Peru and Bolivia, where it thought the plant was domesticated, it is the second most widely grown root crop after the potato. Its development as a food crop may predate the Inca empire.

Oca is a perennial plant with leaves like a bigger version of its relative Wood Sorrel, Oxalis acetosella, and knobbly root tubers which come in a variety of colours: white, cream, yellow, purple, pink, orange and red, in a varety of patterns and combinations. The tubers vary in the amounts of oxalic acid they contain, and some varieties need to be soaked and/or left out in sunlight before they are edible. My Oca tubers are pink and have a slight acid tang which fades when they are cooked.

Oca can be grown in the UK, where it prefers well drained or loamy soils. The plant is adapted to the short day length of the tropics and needs a day length of twelve hours or less to form its tubers. This means that tubers only start to form in September and a couple of months need to elapse before there is a crop worth harvesting. The first sharp frost will kill off the leaves and then the tubers will continue to grow for a couple of weeks afterwards. I accidentally left a few small tubers in the ground last year and each one produced a respectably sized plant the next year, so it should be possible to keep tubers in the ground over winter, at least in sandy soils. You can cover the plants with fleece or even their own frosted foliage, to protect the tubers.

I start my tubers off in small pots in peat free compost and then plant them out about a foot (30cm) apart in early June after the first frosts. Growth is slow to start with and until August the plants form discrete, round clumps. Later on they start to spread out across the soil. Some varieties have pretty yellow flowers but my variety hasn’t flowered. If it is very dry in August and September, it is a good idea to water the plants.

Oca

Oca (left), early August 2015

As tuber growth doesn’t start until late summer it should be possible to plant Oca as late as early August, perhaps after harvesting an earlier crop such as garlic, or interplanting with other crops. The Down The Plot and Growing Oca websites have some good suggestions for timing when to plant. The Growing Oca website also has some tips for increasing the yield. Thompson and Morgan suggest that yields of 1.6lb (0.75kg) per plant may be possible in a good year in the UK.

Unlike potatoes, I don’t bother earthing up my Oca plants. The tubers are shaped rather like “Pink Fir Apple” potatoes but they are not susceptible to potato blight. The leaves are good at suppressing weeds as well. Although the tubers are smaller than potatoes, they have a waxy skin and are easy to clean and I never bother to peel them.

I try to lift my entire crop of Oca and store the tubers in a frost free shed. Potato tubers go green in light and produce the poisonous glycoalkaloid solanine but Oca tubers can be stored in the light. They will start to produce sprouts in the spring, but more slowly than potatoes. They will gradually dry out during the winter, but only very slowly in a cool place.

Oca

Oca plant, lifted, November 2015

Update 6th December 2015: This year, as an experiment, a Canadian friend harvested her Oca plants in mid-November. Rather than immediately putting the tops on the compost heap, she left the smaller tubers attached and hung them up in her garage for three weeks. At the end of this time even the tiniest of tubers had grown in size as they absorbed nutrients from the dying foliage. If you have space, especially if growth is stopped by an early frost, this is well worth a try.

Cooking and Eating

Oca tubers have an excellent flavour. They can be eaten raw, when they have a zingy, slightly acid taste. (Leaving them in sunlight for a few days will make them sweeter.) They can be cut into small pieces and boiled for five to ten minutes, parboiled and mashed or roasted in the oven with olive or sunflower oil. The acidity fades when tubers are cooked: boiled tubers taste like waxy potatoes with a hint of lemon and roasted tubers are like a flavoursome roast potato. Oca is good roasted with other vegetables.

I can recommend Oca Salad with Capers and Cornichons and Warm Oca Salad but I haven’t tried Oca Homity Pie yet. Last night I cooked Hugh Fearnley-Whittingstall’s vegeree recipe and substituted the courgettes (now out of season) for Oca. Coated with spices, the tubers combined well with roasted aubergine and red onion.

Oca tubers contain significant amounts of Vitamin C, zinc and vitamin B12 and some varieties are also high in iron. They are a low calorie food too – 100 grammes of potatoes contain about 75kcal but the equivalent weight of Oca contains around 30kcal. Yet more good news is that although they resemble small Jerusalem artichokes, Oca’s storage carbohydrate is starch rather than the inulin found in Jerusalem artichokes, so Oca does not have the same gaseous side effects when eaten.

The leaves and young shoots can be eaten as a tangy green vegetable, though not too frequently because of the oxalic acid they contain. The flowers are also edible and look very pretty in salads. Mature stems can be used like rhubarb.

Further Reading and Growing

If you want to read more, I suggest you look at the Oca Links page of the Growing Oca website. You may also be interested in the Guild of Oca Breeders (GOB), who are trying to breed day neutral varieties of Oca, which will produce tubers much earlier in the year. The first potatoes were late cropping short day plants but intensive breeding has produced potato varieties that crop as early as mid summer – it should be possible to do the same with Oca.

If you live in the United States or Canada, the Cultivariable website offers several varieties of Oca.In the UK, The Real Seed Catalogue sometimes sells Oca, as well as other unusual tubers such as Yacon. Thompson and Morgan sell Oca tubers that look like the variety I’m growing. Although tubers can be expensive, you should only need to buy them once if you grow your own.

The Blooms ‘n’ Food website has some great photos of the different stages of growing Oca.

Oca – Not Okra!

When I say the name people sometimes think I mean Okra, or Ladies’ Fingers, whose slimy seed pods are used in gumbo and many other dishes. This is a very different plant to Oca. Okra, Abelmoschus esculentus, is a member of the Mallow family, the Malvaceae. It is related to Hollyhocks, which I wrote about in my previous blog post.

Hollyhocks, Alcea rosea

Jeremy Bartlett's LET IT GROW blog Posted on by

Hollyhock

Cold north-west winds are bringing showers of rain and, later, perhaps a little sleet or snow. It’s a day for staying indoors in front of a fire. But outside the kitchen window, dried seedheads of Hollyhocks move in the breeze and remind me of the glories of summer.

Hollyhocks, Alcea rosea, are magnificent plants. Short-lived perennials in the mallow family, Malvaceae, they grow upwards from a few basal leaves to form a flower spike six feet (two metres) or more, often reaching nine feet (three metres) tall. The flowers come in various colours – shades of pink, white, red, yellow and even a dark maroon that verges on black. They are an essential cottage garden flower.

Hollyhocks like well-drained soil and even thrive in cracks in paving and in gravel. A Hollyhock does best when it has enough root depth – a deep tap root enables the plant to reach deep underground for water and nutrients, as well as anchoring the plant against the wind.

Hollyhocks are easily grown from seed. If you sow seed in late June or early July in a seedbed in the garden or a seed tray of peat-free compost, you should have seedlings ready to plant out by the end of the summer. Seed can also be sown in a cool greenhouse in late summer and the seedlings planted out in spring. Either way, the plants will flower the next summer, from June onwards.

Packets of mixed flower colours are available and I enjoy the whole range of colours that are available.

I will only grow Hollyhocks with single flowers, such as the one pictured above. I tried to buy Hollyhock plants from my local garden centre a couple of summers ago, but all the plants had double flowers. These are a lot less attractive and are utterly useless to bees and other pollinating insects.They are best avoided. Unfortunately, double flowered Hollyhocks are available in most seed catalogues as well.

A Hollyhock plant will flower several times, but after a few years it will die off. Some authors recommend cutting off the spent flower spike after flowering, as a way to prolong the plant’s life. However, the plant will die after a few years anyway and leaving the spikes alone will allow your Hollyhocks to self seed. Self-sown plants often crop up in interesting and unexpected places and come in unexpected colours, which to my mind increases their interest in the garden. Self-seeding means there is no need to keep buying seed, either. (If you don’t like Hollyhocks or have too many, the young seedlings are very easy to pull out, so this habit of self-seeding is not much of a nuisance.)

Hollyhock

Hollyhocks are edible. The young leaves have a mild flavour and can be eaten raw or cooked, although the Plants For A Future website admits that “the texture leaves something to be desired”. The flower petals and flower buds can be added as a raw ingredient to salads, adding colour more than flavour. The root contains starch and a refreshing tea can be made from the flower petals. A Hollyhock infusion may be used to treat a sore throat and a poultice can soothe inflammation.

Hollyhocks have one drawback: Hollyhock Rust, a fungal infection by Puccinia malvacearum. The fungus also infects other members of the Malvaceae, including Malva, Abutilon, Hibiscus, Lavatera,  Malvastrum and Sidalcea. My Hollyhocks show symptoms every year, as does my Musk Mallow (Malva moschata). Yellow or orange spots appear on the upper surfaces of the leaves, with reddish-brown pustules on the lower surfaces. The pustules spread onto the stems and calyces of affected plants. The disease is rather unsightly and can reduce the vigour of plants.

Hollyhock Rust appears to be almost inevitable, as the basidiospores produced by the fungus easily spread in air currents from one plant to another and to Hollyhocks from other species including the Common Mallow, Malva sylvestris, which is a common weed in our area. Some authors recommend the use of fungicides but I don’t use them and I’m happy to have rusty Hollyhocks – there are many worse things and the flowers of infected plants still look lovely. Several fungicides previously recommended for use against Hollyhock Rust are now being withdrawn and, anyway, spraying with fungicides may suppress the fungus without killing it, so plants will still pass on the infection.

Feeding Hollyhock plants with compost in spring will help them to grow stongly and not suffer too much from rust. Ensuring good air circulation can also discourage rust.

We leave our Hollyhocks’ dead flower spikes over the winter and by doing this we have  provided a home for the larvae of the Hollyhock Seed Moth, Pexicopia malvella. This tiny moth (wingspan 17-20 mm) flies from early June to mid August and we recorded it in the summers of 2014 and 2015 in our back garden. Its larvae feed inside Hollyhock seeds (and those of Marsh Mallow, Althaea officinalis) and then overwinter in a cocoon constructed inside the larval workings.

The species is rare and is in decline. This might be partly because fewer people grow Hollyhocks these days and those that do may be destroying the moth’s habitat by cutting off flower spikes after flowering. The moth may also be overlooked, as it is not the most colourful and spectacular of insects. Without the excellent Norfolk Moths and UK Moths websites and the book “Field Guide to the Micro-moths of Great Britain & Ireland” by Phil Sterling and Mark Parsons, illustrated by Richard Lewington (British Wildlife Publishing, 2012), we would have been unable to make an identification.

Hollyhock Seed Moth

Hollyhock Seed Moth, Pexicopia malvella

In Norfolk, the Hollyhock Seed Moth was recorded at Hickling Nature Reserve from 1957 until 1989, in Norwich in July 1987 and in the Berney Marshes / Reedham area in 1994. Ours are the first records since. Thanks to Tony Irwin (who recorded the moth in his garden on Earlham Road in Norwich in 1987) for taking a look at one of our specimens (pictured above) and confirming the identification.

Salvia ‘Hotlips’

Jeremy Bartlett's LET IT GROW blog Posted on by

As autumn advances the garden is slipping from summer into winter mode. On the allotment, I’ve taken down all the bean frames and dug out the squash, courgette and sweetcorn plants and even the Cosmos and Dahlia flowers are looking windswept and past their best.

In the big raised bed in our front garden, however, the flowers keep on coming. Particular stars at this time of year are Mexican Fleabane (Erigeron karvinskianus) and Salvia ‘Hotlips’.

Salvia 'Hotlips'

Salvia ‘Hotlips’ in our raised bed.

Salvia ‘Hotlips’ is a woody sage from Mexico. It is usually considered to be a form of Salvia microphylla, Blackcurrant Sage, although it is sometimes (as on the Thompson & Morgan website) classified as a form of Salvia x jamensis (a hybrid between Salvia microphylla and Salvia greggii). I’ll skirt around the naming problem by just using the name Salvia ‘Hotlips’.

Salvia ‘Hotlips’ is very drought tolerant and flowers from early summer until the first hard frosts. It is described as being semi-hardy and will grow happily outdoors here in Norfolk, although it will lose many of its leaves in the winter. It does best in a well-drained soil in a sunny spot and a prune back in spring, to tidy it up and remove twigs that have died off in winter, will keep it happy. In a colder area you can grow it in a pot and take it into an unheated greenhouse for the winter to keep it drier and slightly warmer – it is usually the combination of cold and damp that more tender plants dislike. If you grow it in a pot, repot it once a year and give it a regular feed in the summer months.

The name ‘Hotlips’ comes from the colour of the flowers, which are white with dramatic red lips, the colour of a garish lipstick. Depending on the conditions in which the plant is grown, the flowers can vary between bi-coloured red and white, pure red and pure white.

The flowers are attractive to bees. The nectar is at the bottom of the tube of the flower and a bumblebee can reach it by pushing down on the lower petal and crawling inside the flower. Short-tongued bumblebees often find it easier to “cheat”, by biting a hole in the base of the flower to steal the nectar. This is quite literally robbery: the bee takes the nectar without pollinating the flower. We recently spotted a Buff-tailed Bumblebee (Bombus terrestris) queen doing this on our plant.

The leaves have a pleasant blackcurrant smell when bruised: Salvia microphylla is sometimes known as Blackcurrant Sage. The flowers taste pleasantly sweet and small numbers can be used to decorate salads and the leaves can be used fresh or dried as a flavouring. A herbal tea can be made from the leaves, called ‘mirto de montes’ (after the name commonly used for the plant in Mexico, meaning ‘myrtle of the mountains’). Medicinally, the leaves can be used to reduce fever.

In recent studies extracts from S. x jamensis have been shown to be cytotoxic (toxic to cells) and phytotoxic, inhibiting the germination of poppy (Papaver rhoeas) and oat (Avena sativa) seeds. The essential oil of the hybrid Salvia x jamensis contains at least 56 different compounds.

Salvia ‘Hotlips’ was first made available to gardeners in 2002 by Stybning Arboretum, now known as San Francisco Botanical Garden at Strybing Arboretum. The original plants were brought to the United States from Oaxaca, Mexico, after a housewarming party given by Richard Turner, the editor of Pacific Horticulture Magazine. His Mexican maid, Alta-Gracia, had provided flowers from her garden for the party, including those of this lovely plant.

There are many other varieties of Salvia microphylla and its near relatives, so even if you think that Salvia ‘Hotlips’ is a bit too vulgar for your garden, you can grow one of the others, although the hardiness of different cultivars varies: from 1 to -10 Celcius. I have the purple-flowered Salvia ‘Christine Yeo’ in a pot and also a pink-flowered Salvia microphylla, which I bought from Natural Surroundings many years ago. It did well in pots and even better in the garden. There are also many other species of late summer flowering Salvia to choose from.

New plants of Salvia ‘Hotlips’ and its relatives are easy to raise from cuttings in late summer and early autumn. One of the pink-flowered plants that I raised from cuttings has done very well in Grapes Hill Community Garden, just inside the gate. If you’re unsure whether your particular plant will be hardy where you live, taking cuttings and keeping them frost free over winter is a good insurance policy.

Salvia microphylla

Pink-flowered Salvia microphylla in Grapes Hill Community Garden