When his mound-garden grew, this gardener got the last laugh

In the West German town of Pforzheim, Wolfgang Romhild turned a small plot of compacted, almost-sterile clay into ''a garden of abundance,'' to quote his neighbors and everybody else who stopped by to gaze over the fence.

His accomplishments, in the face of initial ridicule from the so-called experts in the community, were first reported in the German magazine Obst und Gartenbau (Fruit and Garden Cultivation) in 1977. Just how he built his garden then is well worth knowing today.

It seems that Mr. Romhild had often watched trucks piled high with grass clippings from the manicured lawns of the region drive out of the city limits to dispose of their contents at the city dump. It seemed like an unconscionable waste to him, so when he was given a plot large enough in which to garden, he resolved to make use of some of that grass.

Romhild was aware of the classical German mound-gardening system, which made use of woody materials and cow manure covered by a layer of soil, but he had no way of getting these materials other than buying them, which would have been expensive. So he substituted grass clippings, and the results were beyond his, and apparently everybody else's, expectations.

Romhild made his beds by excavating a broad, shallow trench, 5 feet wide, 10 inches deep, and as long as his small plot would allow. Into this he dumped a high mound of grass clippings with some leaves and soil mixed in, topped by a 4 -inch layer of soil. Because the beds were made in the spring with moist, fresh clippings, there was no need to add much water to the bed other than the light sprinkling needed to settle the soil on the top. A week later he began planting.

When the beds were being built, some people walked by in head-shaking disbelief. When he set out the young plants, many tapped their foreheads to indicate the stupidity of the whole idea.

''Much too close,'' was their comment on the plantings.

But two things were happening in those mounded beds, which he had set out on a north-south axis so that both sides would benefit from the direct rays of the sun:

* The very process of decay going on in the bed added much-needed warmth to the soil during the cool spring weather.

* As the grass decayed, a rich supply of nutrients was released to the growing plants. Everything grew with such lush vigor that even the most skeptical of the experts ''admitted their mistake.''

Significantly, Romhild found that gardeners with little or no formal background in horticulture had no problems accepting the idea from the very beginning.

Mounded beds made largely of grass, apparently, give impressive yields for one year only. ''They are exhausted after one growing season,'' says Romhild, ''so you must begin all over again the following year.''

If leaf mold is used in place of the grass, however, the bed will be productive for two full growing seasons. In contrast, the classical German mound bed will last five seasons.

The base of these beds is composed of wood chips or a woody material such as hedge clippings. On top of this goes a layer of upturned sod, generally taken from the area where the bed is being made, followed by leaf mold, decayed manure , or both. Soil is scattered between each of these layers, and a 4- to 6-inch layer of compost-enriched soil goes on top.

The soft and spongy nature of all of these mound beds allows both moisture and air to penetrate easily. Roots readily penetrate the medium and, because of the rich concentration of nutrients, plants can be set out closer than in conventional soil beds.

Romhild now makes his beds of garden waste, to which are added grass clippings and some leaves. Subsequent experiments have shown that these beds become even more productive if the various layers of organic materials are sprinkled with composting bacteria, sold at most garden centers.

When inoculating the beds with bacteria, Romhild has found that he can include some newspaper and cardboard in his mound gardens. He has made compost in which 50 percent of the ingredients were newspaper (black-ink pages only), cardboard, or both.

Earthworms abound in these beds, and Romhild has found that they work right up to the surface of the soil, enriching it ''all the way to the top'' if a light mulch of grass or even sawdust covers the bed.

Romhild's philosophy on gardening goes much further than soil-enrichment and vegetable production.

''Ever since starting the garden,'' he says, ''I have consciously given away (vegetables).'' The results of this generosity show in still better yields from his garden and considerable reciprocal generosity toward him.

''Often I would give away some surplus vegetables in the morning to visitors to my garden. In the afternoon a case of coveted fruit would be standing in front of the house.

''The world is so rich,'' he concludes.