Summer's flowers are the brightest and the boldest in the garden, as radiant as the sun itself. Most need heat (the two most popular, marigolds and zinnias, come from sunny Mexico), and they shouldn't be planted until the weather promises to stay warm.

Two of the brightest summer annuals--marigold and gloriosa daisies--come in many forms. There are small-flowered French marigolds, big American hybrids, and just about every size between them. Summer's flowers aren't quite as easy to grow as those of spring. Warm weather brings out bugs and disease that may bother them, and regular watering becomes more critical, but they are a tough lot--born to grow in the sun. The following is a list of some of the best annuals for summer.

Ageratum: Flat, fuzzy clusters of violet-blue flowers cover this foot-tall plant throughout the summer. Good as a filler, or in the front row. Best planted from packs or pots.

Sweet Alyssum: As good in the summer as it is in the winter and spring, it grows in low mounds of white or purplish flowers. 'Midnight,' a dark purple variety and 'Wonderland,' a pinkish purple one, are less likely to fade in summer's heat. Dwarf kinds are dense, stay under four inches. Best grown from seed.

Cosmos: Bushy plants with vivid, daisy-like flowers on long, thin stems. There are two distinct kinds, one with brilliant yellow or orange flowers and one with flowers in shades of pink, mulberry, and white. Both have the same airy effect in the garden, growing to three feet tall or more. Easy to grow from seed, packs or pots.

Gloriosa Daisy: Huge daisy flowers on tall but graceful plants growing to four feet. Flowers usually golden, often with dark mahogany markings, though some are completely mahogany in color. 'Irish Eyes' has a bright green center. Easily grown from seed, packs or pots.

Lobelia: Six-inch-tall plants, often with dark reddish foliage and bright blue to violet flowers. A good filler that contrasts nicely with summer's many golden flowers. Best grown from packs or pots.

Marigold: Summer's favorite flower hardly needs describing. They come in many shapes, sizes and colors. Marigolds are easily grown from seed, packs or pots.

Portulaca: Low-spreading succulent plants with shimmering flowers almost too brilliant for the garden, in shades of yellow, orange, red, cerise, coral, and white. Loves hot weather. Easy to grow from seed or packs.

Verbena: Usually planted as annuals, except in warm climates. The kinds sold as bedding plants have rounded clusters of white, pink, red, or violet flowers, grow under a foot tall, and should be planted two feet apart. They are seldom out of bloom. Very useful in the foreground of the garden. Best grown from packs or pots.

Vinca: The best annual for really hot weather, it is also long lasting, well into cool weather. A foot tall with neatly growing white flowers with red eyes or rosy pink flowers. Best grown from packs or pots.

Zinnia: The brightest of summer flowers, zinnias come in many sizes, forms and colors. All come in brilliant shades of yellow, orange, pink, rose, scarlet, cream, and violet. Prettiest when planted as a mix of colors. Easy to grow from seed or packs. Will become root-bound in pots.

If you'd like to have some water lilies but don't have a pond, try this.

Purchase a water lily planting tub, or make your own from a plastic or cardboard container that is 14 or 18 inches in diameter and 6 to 12 inches deep. Plug the drainage holes with wads of two layers of newspaper. Containers can also be made from plastic baskets like small laundry baskets. Line them with polyester quilt batting. Plant water lilies in rich garden soil; fertile loam is best. Make sure it contains no manure (which encourages growth of algae) and no peat moss, compost, commercial potting soil, perlite, wood shavings, or other lightweight soil amendment that might float to the surface of the pond.

According to package directions, mix into the soil a complete, slow-release, granulated fertilizer that's recommended for aquatic plants and contains trace elements to enhance growth and flower color. Or choose a generic complete fertilizer such as 10-20-5, and mix 1/4 cup of it into every 3 gallons of soil. Be sure the fertilizer you use contains trace elements, but no herbicides or pesticides.

Fill the container to 2 inches below the top with fertilized soil, and then water it so that it settles. Add more soil if necessary. Plant one lily at a time and keep all others moist and in the shade. Don't let their roots dry out. Plant water lilies when the water temperature is 70 degrees or higher. Place the tuber in the center of the container with its roots buried and its crown, the place from which the foliage emerges, protruding slightly above the soil. Protect your lilies from fish; fold some poultry wire over the container with a hole in the center about 4 inches in diameter. (If your lily already has foliage, cut the wire in half first and tie the two halves together, protecting the plant).

Immediately after planting carefully submerge the lily in the pond 4-6 inches of water above the soil level. When the plant grows to 8 inches in diameter, lower the container so there are 12 inches to 18 inches of water above it.