Ask the gardeners

For the past two years we have had a lovely bed of red geraniums and dusty miller, both of which we started from seeds. This year we would like to edge the bed with a short blue flower that we can either start from seed or get in plant boxes at a garden store. What do you suggest?

It is a bit late to start lobelia from seed, but you can buy the started plants, which will continue to bloom all summer long. Two beautiful compact varieties are Crystal Palace Compacta (deep, solid blue) and Mrs. Clibran (deep royal blue with white eye). Both combine well with short varieties of dusty miller, which will make a handsome blue-and-silver border.

Blue ageratum is a possibility, of course, but it has a tendency to go out of bloom if not kept groomed; and it also falls prey to spider mites.

Lobelia will grow in either sun or shade.

Please give me the name of the strongest onion there is. I want to make an onion spray to use for insect control on my plants.

Some onion varieties have more sulfur compounds (the ''tear jerkers'') than others. Old-fashioned Ebenezer is one of them.

You can also get ''hotter'' onions if you grow them on the dry side. Thus, try watering them less often. Stay clear of the large sweet onions which are mild.

We'd like your formula for onion spray so we can print it in this column along with some sprays which use garlic and hot pepper.

Last summer our Brussels sprouts grew well, but when we harvested them, they were somewhat bitter tasting. What caused the bitter taste?

Too dry or too wet weather can cause this condition, but cooler weather will usually sweeten them up.

Try this trick. In late summer when the lower sprouts are beginning to fatten up, pinch out or whack off the growing tip with a stick. This stops growth and sends the strength into each sprout, thus making it develop quicker.

Leave the plants in the garden until you've had several moderate frosts. You'll be surprised at the improved flavor.

Peter Tonge said in a recent article on onions that he planted in the top 2 inches of soil, only scratching the soil up enough in which to plant. By this method he did not bring deep-lying dormant weed seeds to the surface. Each spring I have tilled the garden to break up our rather clay-like soil and aerate it. What do you say?

Peter's method of nontilling is good for soils that are not heavy clay. It sounds as if your soil is the heavy type and you will need to break it up with your tiller.

No doubt you will bring up some weed seeds (an acre has about 3,000 pounds of them lying dormant). With your machine, you should be able to cultivate between the rows and eradicate most weeds.

We suspect Peter uses a good mulch between the rows to smother out any weeds that do come up.