Gardening: Nice and comfrey

Comfrey is famous for kick-starting potatoes and infamous for creating a giant stink as it rots in your liquid manure. Photo / Waihi Leader

If you really want to succeed at organic gardening, there's a herb you should know, writes Justin Newcombe.

If you consider yourself serious about all this gardening get-up then make sure you get yourself some comfrey plants this summer.

Comfrey is a bit of a weed once it becomes established, but don't let that stop you from giving it a go.

It is an undisputed hero in your organic gardening arsenal. Extremely high nutrient levels, combined with healing properties have made it popular in many cultures for centuries.

Comfrey is a nutrient glutton, coming third only to nasturtium and nettles on my table of beneficial weeds. Although it contains fewer actual nutrients than the other two plants, its concentrations of nitrogen are quite staggering, equal to that of farmyard manure. It has similar levels of phosphorous and twice as much potassium. The leaves are also high in vitamins B,C and E and beta-carotene. With those jaw-dropping levels of potassium it makes an ideal fertiliser for any fruiting plant which at this time of year that means tomatoes, peppers, cucumber, melons, potatoes - in fact, any other plant you can think of that bears fruit. The leaves can be used directly on the garden as mulch or you could add them to your compost or liquid manure barrel. It is best to harvest the leaves just prior to flowering as this is when the nutrient levels are at their highest. More annoyingly, the flowering stems are capable of taking root so you need to avoid them getting into your garden beds or compost. Comfrey is famous for kick-starting potatoes (line the trench with wilted leaves) and infamous for creating a giant stink as it decomposes in your liquid manure.

Comfrey has long been used for medicinal purposes as well as gardens. Back in the olden days people would make it into tea and drink it, or eat the young leaves raw, but today this is no longer recommended because tests on rats have deemed it carcinogenic if eaten. It has also been linked to liver damage. Its folk names - knitbone or bruisewort - give a clue to its other use as a poultice or compress for sprains and aches, swelling and bruising. Apparently it is magic on haemorrhoids and varicose veins as well, but I am not speaking from personal experience. The active ingredient in comfrey is allantoin, which repairs tissue, and reputedly has anti-inflammatory properties. If you keep chickens then comfrey is said to be a good natural worming remedy and conditioner for the girls.

Comfrey has a rampant taproot which allows it to mine nutrients from deep beneath the soil - great when it comes to creating a fertiliser for your garden. It is, however, potentially invasive and care should be taken to minimise its spread throughout your garden.

The trouble can start when plants are dug up for removal or (heaven forbid) transplanting. Any small root fragment left in the soil will grow. The flip side is that it is virtually indestructible and it will outgrow other less desirable weeds, making it an effective weed barrier. It will die back in winter though.

I've never had to feed my comfrey plants and the thought seems a little ridiculous given their rampaging tendencies, but apparently it is quite tolerant of the odd application of urine diluted 50:50 with water.