During the last decade increased production has occurred in horticulture under glass in the Netherlands. This results in a desired enlargement of the holdings and lots so as to bring about a more rational use of labour, capital and land. In addition, more attention is being paid to the impact of increasing energy prices, especially in connection with the length/width ratio of glasshouses. The total area of horticulture under glass increased from about 5,000 ha in 1960 to nearly 8,500 ha in 1979. From 1965 onwards the number of holdings with horticulture under glass decreased. Consequently the area of glasshouses per holding increased considerably. It is shown that the profitability of cultivation of vegetables and cut flowers was decreasing in the period considered. The cost components, as a percentage of total cost, remained more or less constant, though the cost of labour rose over 800% in this period. In spite of the large rise in cost of energy since 1973 the trend to use more intensively heated glasshouses is still in progress. As a result of changing production conditions in horticulture under glass, present land layout conditions are often outmoded. An attempt is made to quantify cost factors depending on the width and the size of the lot (and the glasshouse), and the results are graphically presented by way of iso‐cost curves. It may be concluded that a lot smaller than 1.25 ha (glasshouse size approximately 1.00 ha) or having a width of less than about 60m (glasshouse width approximately 55m), does have higher unit cost of production. In this respect, many holdings in the Netherlands are not operating under conditions where an ideally efficient management is possibl