Rhubarb, asparagus and globe artichokes
Rhubarb, asparagus and globe artichokes are all perennial vegetables needing a permanent location in the garden. Before planting them out, it is necessary to ensure that the soil is free of perennial weeds. Permanent mulching will enable the beds to be kept weed free.
Rhubarb is useful to the organic gardener, not just for its culinary and wine making attributes. The leaves are extremely toxic to livestock, people and some insects. This latter enables the gardener to make a cheap and useful insecticide.
Boil 400 gms leaves in 1 litre of water for half an hour. Strain and add a little soft soap (potassium soap, Clensil or Safers). Dilute one part of solution to one part water. This spray is safe to bees and lethal to aphis.
Rhubarb crowns are available in winter from most nurseries and are planted out with the eye, or incipient bud, just showing above the ground. Feed and mulch the ground heavily. Make only a light picking the first spring. Remove flower stalks as they arise as they weaken the plant. Allow 1 metre between rows and 600-800 mm between plants.
Alternatively, rhubarb seed can be sown in the spring and the plants sorted for colour and vigour. The seed is sown in shallow drills in a seedbed and any that are poorly coloured are removed during the growing season. The following winter they are planted out in their final position.
Once every four or five years the plants should be lifted and the crown broken into pieces with a sharp spade, leaving one eye per piece. This is then replanted in the same or new ground to grow on.
Asparagus needs to be off to one side of the garden, as its tall feathery foliage will shade nearby plants. It can be grown from seed in early spring. The seed is soaked overnight in water to speed germination and sown about 75 mm apart in drills. In the second season after sowing, the female plants will flower and these should be removed. The male plants produce more vigorously and the spears are thicker. Alternatively, crowns can be purchased in winter.
Asparagus needs perfect drainage to do well, which means raised beds in heavy soils. Mix as much compost or rotted animal manure as possible with the soil before planting. This vegetable also has a very high calcium requirement and liming to a pH of 6.5 to 7.0 is essential. Each winter, the foliage should be cut off and composted. The mulch should be renewed and compost applied as heavily as possible. A well looked after asparagus bed will produce for two decades or more, so it is worthwhile to install underground drainage in poorly drained sites.
When planting out two-year-old crowns, place them 150 mm deep in rows 900 mm apart with 300-400 mm between plants. Take only a light picking the first season to give the plants time to build up their reserves. Cut the spears carefully to avoid damaging nearby juvenile spears. Cut below the surface of the mulch. When the plants are in full bearing, they can be harvested until the first peas are picked and then they should be allowed to grow on to store nutrients for the following season.
As they originated near the sea, salt is sometimes used as a weedicide around asparagus beds. If you do this, be sure that the drainage from the bed does not go near plants sensitive to salt.
Globe artichokes are tall, attractive, vigorous thistle-like plants and can make an excellent summer windbreak. The plant is grown for its immature flower buds which are a delicious spring treat. They should be eaten before the buds start to open. They are either grown from sets in a way similar to rhubarb division, or from seed. The seed is sown in spring 25 mm deep in rows 300 mm apart and 100 mm between plants. The following year they are transplanted to their final position in rows 2000 mm apart with 1000 mm between plants. They should be composted and mulched heavily. Suckers arising from the base of the plants should be removed. These are used to renew the planting every two or three years. Under optimum growing conditions, artichoke plants will produce for five years. Cardoons are a less vigorous type of artichoke and can be treated the same way.