Palmaria palmata, also known as dulse, is a relatively rare seaweed that grows in the waters of the North Atlantic and Northwest Pacific oceans. It clings to rocks in areas between high and low tide, and sometimes on exposed shores. The primary producers of dulse for consumption are the United Kingdom, Norway, Iceland and parts of Canada. It has been cultivated on ropes, but only by large companies or professionals. If you don't have access to the extensive supplies needed for true cultivation, you can look into Home Photobioreactors or try to harvest naturally growing dulse off the coast. It is easy to recognise with its flat, leathery, reddish-brown fronds. These instructions are based on experimentation done off the Spanish coast.
Suspend ropes from vertical rafts in open sea. Use weights and buoys to keep them stable and secured.
Attach the growing fronds to the ropes. Some people choose to insert them directly into the rope, but others have found that putting the fronds in a mesh bag is more productive and prevents loss. Make sure your fronds are not too tightly packed, otherwise the growth will be limited by space and available resources.
Give the fronds about 4 to 6 weeks to cultivate. Spring or summer is the best growing season. Add nutrients, if desired, for maximum growth.
The method above was attempted successfully in northern Spain. Dulse will only grow in specific climates and temperatures.
Open sea cultivation should not be attempted without the appropriate permits and credentials. For most people, it is best to purchase dried dulse.