Seaweed is classed as a soil conditioner in the gardening world, but its benefits are so extensive that it really should be given top billing when discussing the care of soil and growing of plants, as it contains over sixty minerals and trace elements, along with bio stimulants.
It can be used in many forms, ranging from being dug into your soil straight off the beach, through being dried and granulated or powdered, to many different liquid formulations.
Many links golf courses used to take seaweed from the adjacent beaches and cover greens with it during severe winters, which both protected the grass from the cold and provided a range of nutrients as it weathered down. When the weather improved the seaweed was removed and composted with sand to provide a very high quality topdressing material. Now, play continues all year round on most courses, so this practice is not feasible but, if there is seaweed available, then it is most certainly well worth harvesting and composting to provide your own supply of high quality topdressing material.
It is also a valuable addition to divoting material, as germination and establishment is dramatically enhanced. In fact, I always advise adding seaweed meal or granules to the divot mix, as it is of great benefit on any golf course.
In my time as Links Superintendant at Lahinch, the beach and adjacent shorelines were constant sources of clean, high quality seaweed as, being on the atlantic coast of Ireland, there was no land between there and America.
We almost lost a tractor in the tide collecting the seaweed at one stage, but the effort was always well worthwhile. The seaweed was used to build large heaps, as pictured, with a layer of seaweed around 30cms thick, then a layer of our own dune sand around 10cms thick, with these layers repeated until the heap was around two metres high. Each heap was then turned over four times in the following year, then taken into the first of the three composting bays to dry out.
After a few weeks of drying, the compost was then put through a Royer shredder into the second bay, and left for a further few weeks before the final step of screening into the third bay, at which stage it was ready for using as topdressing and for divotting. Fantastic compost, prepared from beach to usable in just over a year.
Seaweed contains a wide range of nutrients and trace elements which combine in such a unique manner that, when seaweed is added to heavy clay soils, it acts as a floculator, which means it breaks down the heavy soil into a friable crumb structure, thereby providing a vastly improved growing medium. This, of course, does not happen overnight, but is one of the greatest benefits of long term applications on these types of soils.
On the other side of the coin, seaweed is an excellent addition to sandy soils, adding to the humous content and nutrient levels, and increasing drought resistance. Because of my experience, I do believe, in fact, that adding seaweed to the rootzone mix in any USGA green construction does alleviate the many problems, such as take-all patch and nematode discolouration that are inherent in a high sand content material because of the lack of a healthy microbial and bacterial population.
Raw seaweed should only be used in situations where it can be dug directly into the soil. For example, it is fantastic with potatoes, giving a great flavour, and has the added advantage that the iodene content in the seaweed prevents diseases such as scab. The salt content is minimal so does not affect the flavour of any vegetables.
If constructing a new lawn or sports surface, I always add granulated seaweed to the rootzone mix, as I have found it helps to provide a much healthier growing medium.
On established lawns and sports surfaces, it is much more difficult to introduce the seaweed into the rootzone. This is where operations such as forking, hollow coring and, on larger areas, vertidraining will allow the granules to be spread and then worked into the holes.
I have always found slitting, with a combination of chisel tines in the spring and summer, and six to eight inch (15-20cm) knifes in the autumn and winter, distributes the seaweed more evenly throughout the main root area, as well as being the most effective and least disruptive method of deep aeration.
The fine ground seaweed meal should be used on surfaces, as granules can be picked up by the mowers and also hold too much moisture near the surface. I have always found that the ideal time to apply the ground seaweed is in the spring, straight after scarifying, and followed with topdressing.
For the rest of the growing season, liquid seaweed is the best option, as it is an excellent foliar feed and can be combined with other nutrients as and when required. I certainly think this feeding regime is one of the main reasons why I have not had to apply fungicide on any of my golf courses or bowling greens for the past thirty years - with one exception caused by experimenting with a slow release fertiliser many years ago!
One seaweed product I have not mentioned is calcified seaweed which, when ground, is a very good product to use on acid or thatchy wet surfaces, as it raises the pH and helps to dry out the turf. Only, of course, if it is used as part of a structured maintenance plan designed to rectify the underlying reasons that caused the problem in the first place.
I hope this has given you a good understanding of the benefits that seaweed can provide. If you require any more information, or have any comments, please get in touch.
Duncan Gray, Lawns For You.