The colder months are the ideal time to boost our immune systems with good nutrition. With winter approaching, which nutrients are particularly important and how can we make sure we get enough of them?

Dr Nigel Bending, soil scientist, nutritional gardener and creator of ‘Ergrownomics’ self-watering raised planters, suggests planting ‘unbuyables’ this autumn.

‘Unbuyable’ are crops that are unavailable in supermarkets because they are difficult to harvest, rapidly deteriorate and won’t withstand packing, storage, transportation and display.

By growing our own, whether in pots, gardens or allotments, we can add different flavours and textures to the table. Here are his top five for October to December:

1. Winter purslane (aka miners lettuce)

“Winter purslane has six times the omega-3 content of spinach! It is also an excellent source of beta carotene and fibre.

“The crop forms rosettes of spatulate-shaped leaves that are really sweet and succulent.”

2. Winter savory

“Winter savory is an easy-to-grow herb that can be used to reduce or replace added salt, which is useful for those with high blood pressure.

“Its nutrient value is exceptionally high – a 100g portion provides over 200% of your daily calcium and iron requirement and 100% of vitamin A, C, B6 and magnesium requirement.”

3. Red-veined sorrel

“Red-veined sorrel can be used in the same way as lettuce in wraps and flatbreads.

“It has a very high vitamin content, and a 100g portion meets your needs for vitamin A and C.

“It has an amazing, zingy fizzy-lemon taste – think sherbet lemon – and tastes a bit like a Granny Smith apple.”

4. Lamb’s lettuce (aka corn salad)

“Lamb’s lettuce, as well as having high vitamin A, just 100g provides half of your iron and folic [requirements] – making it especially suitable for including in diets before and during pregnancy.

“It’s also a great source of omega-3 and beta carotenes.

“The plant has small ovate, dark green leaves which are slightly nutty in flavour.”

5. Black Spanish radish (aka winter radish)

“The standout feature is its high glutathione content (extremely important for liver function) and a high fibre content.

“It looks unpromising with rough black skin but contains pure white flesh that is moderately hot.”

And finally…

Bending adds: “While the unbuyables offer something different, it’s worth remembering that any crops you grow at home will have a far higher nutritional value than the shop bought equivalent.

“Kale, Swiss chard and mustard lettuces, included in most ‘salad bags’, are likely to have lost between 50-80% of their vitamin C before you get them home.”