To dry dahlias, plumed celosia, zinnias, roses, marigolds, and other flowers with thick heads or delicate blooms, use a drying agent–borax, white cornmeal, rice, or silica gel (available at craft shops). In about a week’s time, the flower petals will be dry and crisp.Click to see full answer. Then, how do you preserve dahlias?Store each clump of tubers in a ventilated box or basket. Fill the box with slightly moistened sand, peat moss or vermiculite and place it in a cool, dry location with temperatures that remain between 45 and 55 degrees F. Check tubers periodically through winter for rotting and drying out.Also Know, when should I dig up dahlias? When to Dig. There is no specific calendar date to tell you when to dig dahlia tubers. They do not mature until late in the summer or early fall. Tubers that remain in the ground longer develop more fully and are more likely to survive storage over the winter. Besides, can you dry Achillea? Dried materials are long lasting and can be used to add warmth and color to the home during the cold, gray winter months. The simplest way to preserve flowers is air drying. Yarrow (Achillea species) Harvest the stems when the flower clusters reach peak size and color. The flower heads should be firm.Can dahlia bulbs be left in the ground? Winter Care Dahlia foliage blackens with the first frost. Dahlias are hardy to Zone 8 and can be cut back and left in the ground to overwinter; cover with a deep, dry mulch. Further north, the tuberous roots should be lifted and stored during the winter.