IN THE GARDEN FALL'S HOTTEST ROSE PACKS A `DOUBLE KNOCKOUT' PUNCH.

Byline: JOSHUA SISKIN

This fall, exciting new plant varieties are appearing in nurseries. Just when you think a certain type of plant has reached the pinnacle of perfection, along comes another hybrid to knock it off its perch.

The 'Double Knockout' rose has done just that, as its sparkling appearance and long bloom time allow it to lay claim to the title of ``most brilliant and durable low-growing rose.'' For some years now, this distinction has belonged to 'Floral Carpet' roses. Appearing in pink, red, apple blossom, white, coral and, most recently, yellow, 'Flower Carpet' roses seemed to have it all: long bloom time, coppery-green foliage and disease resistance.

However, its flower color selection proved to be somewhat weak. It could not really stand on its own and, from any great distance, draw attention to itself. For example, white 'Flower Carpet' roses positively glow against a background of Rhaphiolepis 'Majestic Beauty' shrubs and red 'Flower Carpet' roses provide a sharp contrast to yellow or salmon daylilies; yet, on their own, these roses do not make a bold statement.

Enter 'Double Knockout.' This is a ground cover/shrub rose that will grab your attention without apology. The flowers are about twice as big as those on the 'Flower Carpet' roses. Also, this is a cherry or fire engine red rose that is accompanied by handsome burgundy foliage. Its disease resistance is also without parallel among roses.

'Fusion' impatiens is another relatively new introduction that deserves scrutiny. Its appeal has much to do with its charming moosehead flowers that hang at 45-degree angles. Color-wise, traditional impatiens are more hotly captivating, as the 'Fusion' varieties bloom in understated tones of salmon, coral and pink.

Impatiens should only be planted for another two or three weeks. After that, sudden cold or rain could stunt their growth and lead to their early demise. However, by planting them now, they could establish a strong root system in the next several weeks and survive through the winter. Should the winter be a mild one, they would thrive in it. At this time of year, impatiens can also be planted in a sunnier location than summer-planted impatiens could take.

A wonderful new plant to be placed on the short list of globe-shaped, compact perennials is the dwarf sweet pea shrub (Polygala 'Petite Butterfly'). This virtually nonstop bloomer sports magenta-mauve flowers and stays under 2 feet in height. Its naturally spherical form puts it in a league with the lacy, silver-leafed Artemisia 'Powis Castle,' the perpetually blooming Crown of Thorns 'Dwarf Apache,' as well as Pittosporum Tobira 'Wheeler's Dwarf' and Pittosporum crassifolium 'Compactum.'

Q. I have a concrete patio on which I want to grow potted plants. My main concern is that the plants will outgrow the pots. Can you recommend any types of plants that would last in a pot for a long period of time?

- Andy Roth, North Hills

A. Slow-growing palms would be my choice. If you have sun, plant Mediterranean fan palm (Chamaerops humilis); if you have shade, plant bamboo palm (Chamaedorea Seifrizii); if you have partial sun/partial shade, plant pygmy date palm (Phoenix roebelinii). Aside from palms, consider cycads for full sun and arboreal or shrubby succulents (Yuccas and Agaves) for partial sun containers.