Alan N. of Santa Rosa asks two questions: When it’s time to cut down my sunflower plants, can I chop up the whole plant and dig them back into the soil to add organic matter, or do I need to toss them? Second, I’ve seen some beautiful colored sunflowers, other than the typical yellows. Where can I purchase those unusual varieties?

It would be great if you could incorporate the flower heads, stalks and leaves, back into the soil to add organic matter when the plants are done and the gardening season is over. Most gardeners tend to plant pretty much the same kind of plant in the same place every gardening season. People like certain plants in certain spots because they like that plant — its color, height and other characteristics. But sometimes planting the same plant in the same spot every year causes plant pathogens to build up in that particular area in the garden, which can then cause the host plant to become infected. If the plants are diseased and you didn’t know/see it, you’ve then incorporated the diseased plant material back into the soil. That’s not good. Look carefully at each plant to make sure it is free of disease. Don’t incorporate the diseased sunflower plants to the soil where you plan to grow sunflowers next year. If a plant is diseased, dispose of it.

As for where to get unusual and beautifully colored sunflowers? One place to look is SunflowerSelections.com, which develops these new selections. For more than 40 years, sunflower geneticist Dr. Tom Heaton has been developing ornamental sunflowers for the company, which has an incredible array of varieties it sells directly to the home gardener.

Every sunflower is the result of at least seven years of careful research and plant breeding that Heaton undertakes every season. Thousands of plants are grown each year in their breeding plots. Every single plant is followed from germination through flowering with data meticulously recorded for important traits that determine the type and quality of flower that the customers desire. The astounding range of colors and petal forms from sunflower is owed to their passion to create new flowers. When they are convinced that they have created yet another “new” sunflower that growers and gardeners will appreciate, pure source seeds are multiplied by their staff in strict isolation from other sunflowers before being offered for sale.

The company’s latest develop is the first white sunflower. Procut White Nite and Procut White Lite will be released in November for next summer’s growing season. Burpee’s is featuring a white sunflower called ‘Coconut Ice’ and Baker Creek has an heirloom Italian White sunflower.

Dana Lozano and Gwen Kilchherr are garden consultants. Send your gardening questions to The Garden Doctors, at pdgardendoctor@gmail.com. The Garden Doctors can answer questions only through their column, which appears twice a month in the newspaper and online at pressdemocrat.com.