US bulb growers can learn from the Dutch

In the United States, Great Britain, and elsewhere they have the story all wrong. Little Hans Brinker didn't put his finger in the dyke at all. Sensible youngster that he was, he simply stopped up the hole with a tulip bulb pulled from a neighboring field and went on home to dinner. If nothing else, that theory makes sense to the practical folk around Hillegom, the center of the Dutch bulb-growing industry.

Dykes, dams, and polders have been part of the Dutch scene for almost a thousand years now, and the tulip has been just as typically Dutch for about half that time. The two are inseparably intertwined, and ''we couldn't do without either,'' says Kees Frederiks of the Netherlands Flower-bulb Institute here.

Certainly the polders, reclaimed land from the sea, frequently provide some of the most ideal sandy-clay soils for flowering bulbs - and that includes the daffodil, hyacinth, crocus, Dutch iris, and a host of summer-flowering specimens as well. Indeed, if it sends up a stem with a flower on the end, then the Dutch are almost certain to cultivate it, develop it to new heights, and ultimately export it.

Obviously there is a whole lot more to Dutch success with bulbs than merely the right soil. A consistently moist and mild climate along with the quality of light, particularly around Haarlem, where bulb growing began, make for ideal growing conditions.

Indeed, Holland declines in bulb-growing potential from northwest to the southeast, which is one reason the neighboring Belgians are not the bulb growers the Dutch are. The Germans, for instance, aren't that much better off than the Americans when it comes to a suitable bulb-growing climate.

Right now the mechanical planters are swarming over Holland's bulb fields, setting out the parents of the roughly 5 billion bulbs that will make it onto world markets in time for next fall's planting schedule.

What the Dutch planters are doing now, gardeners all over the northern hemisphere can still do. While October is frequently considered the optimum month for planting in much of the US, ''you can continue planting right up until the soil freezes,'' says Mr. Frederiks, a long-time bulb grower himself.

''As long as the bulb has sent out roots, it can withstand a freeze,'' he says.

Dutch bulbs can grow well clear down to Atlanta, according to a climate chart drawn up recently by the Netherlands Flower-bulb Institute. In lower latitudes good planting temperatures will remain for some while yet.

But much can be done to extend rooting temperatures even in the colder regions. The answer lies in applying a thick mulch over the soil immediately after planting. This locks in the soil temperatures, thus slowing down the cooling of the planting bed. This way October lingers on even into early December as far as the bulb is concerned.

Have you ever noticed how garden soil that is frozen in the late fall will thaw out within a few days of the first snow fall? That is because the snow, filled with trapped air, provides the insulation that allows heat from deeper down to move to the surface and build up enough for the soil to thaw.

A mulch works in much the same way. If the mulch is very thick, say 12 inches of hay or leaves, then some of it will have to be removed in early spring. But, if it is no more than an inch or two thick by the time the snow begins to melt, then leave it intact to slowly rot away and feed the soil. The plants will have no problem pushing through.

Another mulch option is to apply straw or leaves, that will be left permanently in place topped by evergreen boughs to provide additional protection. Remove the boughs in the spring, and leave the remaining mulch intact. The Dutch apply a thick straw mulch to their fields both to feed the soil and to protect it from rain and wind erosion.

While home gardens will seldom enjoy the ideal growing conditions found in a Haarlem bulb field, some things can be done to approach the Dutch ideal. The soil can be improved, whether sand or clay, by adding humus in the form of compost, shredded leaves, or peatmoss. ''Get plenty of humus into the soil,'' says Mr. Fredericks, who suggests adding a handful of bone meal to each planting hole. Come spring, a sprinkling of balanced fertilizer, say 10-10-10, is beneficial, he says.

The bulb, of course, contains everything needed to produce a good flower next year. The onion-like outer layers protect and provide all the nutrients needed by the complete plant - stem leaves, and flower bud - that exists in embryo at the center of the bulb. So why the need for fertilizer? ''Because you will want a repeat performance the following year and for many years after that,'' Frederiks points out.

Recent Dutch market research shows the English to be the top bulb buyers among home gardeners. One in three UK gardeners plant bulbs. The Swiss come next with 1 in 4 followed by the Germans and Dutch with 1 in 5. In the US the ratio is 1 in 10.