Seaweed: nature's nutrient bomb

With about 60 trace elements, growth hormones and fungal and disease preventatives, seaweed is a good all-round fertiliser for spuds that could help you get a great crop this year.
With about 60 trace elements, growth hormones and fungal and disease preventatives, seaweed is a good all-round fertiliser for spuds that could help you get a great crop this year.

This year I'm experimenting growing my spuds in seaweed. Soil is quite sufficient, but by several reports from organic gardening devotees, seaweed is exceptional.

In the past, many farmers used seaweed as a mulch for their potatoes, the nutrient-rich sea vegetable all they needed for fertiliser. But these days the practice is rare because collecting seaweed is fairly labour intensive.

Many organic gardeners still make use of seaweed, though, and home gardeners, growing organically or not, can too.

Seaweed contains around 60 trace elements as well as growth hormones and fungal and disease preventatives. It's a good all-round fertiliser for spuds and it's an excellent soil conditioner as well.

If you're not a commercial operator, it's unlikely you'll deplete your local beach's resources by filling a bag or two of seaweed. But you should be aware of the rules surrounding the collection of seaweed.

Under the NZ Fisheries Act members of the public may collect beach-cast seaweed for domestic use, like the mulching of their garden.

Commercial operations are subject to regulations. That's because seaweed is important for the biodiversity of the beach and its surrounds.

It provides a habitat for many small invertebrates like sand hoppers and other insects, which feed on it. These in turn are food for small fish, as seaweed washes back out to sea, which are themselves part of the food chain for larger fish. Seaweed that dries and blows onto sand dunes decomposes and releases its nutrients back into the environment.

If you respect the ecological role seaweed plays in marine communities, small quantities of beach-cast seaweed collected as you walk along the shoreline is fine.

So how to use it for growing potatoes?

There are a couple of different methods to try. One simple method is to dig a trench and place your seaweed at the bottom of it. Add a layer of soil or compost and sit your seed potatoes on top of this. Cover with soil, then keep mounding up with soil as your plants grow.

You can also do this with tomatoes and rhubarb - that is, place seaweed at the bottom of the planting hole.

An alternative is to wrap the seaweed around the plants as they grow, instead of mounding up the soil. As the plants grow, add more seaweed.

Another method is to cut up your seaweed with garden shears and mix the chopped pieces into your soil. The easiest way to chop it is place it in a pile and just snip away. This soil/seaweed mix is a great medium for containers, though it's excellent for gardens as well.

Prepare your soil now while your seed potatoes are sprouting, and you'll have an excellent garden mix come planting.

Here's another method that's used, this one the absolute easiest. Place several mounds of seaweed on top of your soil, or into a container or trough with excellent drainage, and place seed potatoes on top, each tuber placed 30cm apart. You need add no soil to your containers, though make sure there are plenty of drainage holes in the bottom. Seaweed naturally retains moisture, and with just-seaweed gardening, you need to ensure drainage is good.

Add more seaweed to cover the tubers.

When the plants' stems and leaves are 15-20cm high, add more seaweed so that the tips (about 5cm) are poking out. As they grow further, add more seaweed, again leaving the tips exposed.

This method works well with wire cages as well, but if you've been plagued by wireworms or disease in previous years, you might try growing them this way in containers. Wireworms are the larvae of the common click beetle. Eggs are laid in the soil and the larvae feed underground for 2-6 years, attacking roots and tubers. It's unlikely they'll relish a seaweed habitat, so this is a great way to deter them.

I have seen the results of this container-grown seaweed method. No extra fertilisers were added, and the results were superb. The mix was a little mushy when it came to harvesting, though the container itself didn't have many drainage holes. Two very small potatoes had rotted, but from just one seed potato, cut into four, a harvest of 20 good-sized spuds resulted. With four troughs, each with one seed potato, that supplied a harvest of more than 80 spuds.

As a rough guide, when growing potatoes in containers, allow each spud 9-10 litres of growing space. An ordinary bucket is typically 9 litres. You can put more into this space, but your potatoes will be smaller.

I do love my Agria potatoes, but Swift is a fast-growing variety with short foliage, so it's ideal for containers. It's also the earliest of the earlies so these may be some of your earliest new potatoes. I'm growing these this year, for an all-rounder in the kitchen.

First and second early potatoes are usually best for containers as they are usually done before blight appears. However, growing in seaweed, you may not have that problem.

In any case, early potatoes include Swift, Rocket, Cliff's Kidney and Jersey Benne. Second-early to early-maincrop potatoes include Red King, Maris Anchor and Ilam Hardy and are planted September to October.

The Southland Times