When the first frost blackens the foliage of dahlias (or if a hard freeze is predicted), cut off the stems about 6 inches above the tubers. Carefully dig the clumps with a spade or fork, and and let them dry out of direct sun and wind for a day (not too long or they'll begin to shrivel). Store the tuber clumps whole (you'll get larger plants), or make more plants by carefully separating the tubers from the stem, making sure to include any "eyes" (small, raised nubs near where the tubers attach to the main stem) with each tuber. These are the future sprouts. Store tubers in cardboard boxes or mesh bags filled with peat moss, vermiculite, or sawdust. Keep them in a dark, 35- to 50-degree F location.
Preparing Tools for Winter Storage
Begin preparing tools for storage. Clean the soil off shovels, spades, and trowels using a rag or wire brush, then wipe blades with an oiled cloth. Make sure pruners are free from dirt and plant debris, and wipe down the blades with the oiled cloth. Empty pots of dead plants and soil, adding the debris to the compost pile unless the plants were diseased. In that case, dispose of the plants in the garbage or a location far away from your garden. Rinse pots.
Saving Gladiolus, Crocosmias, and Acidanthera
When finished flowering or when frost kills the foliage, carefully dig the corms of gladiolus, crocosmias, and acidanthera and spread them out in a dry, well-ventilated area at room temperature for two to three weeks. Then remove and discard the old corms. Store the new corms in paper bags in a 35- to 40-degree location.
After the foliage has been damaged by frost, allow cannas to dry in the ground for a few days, then cut back the stems to 3 to 4 inches and carefully dig the rhizomes and let them dry at room temperature for a few days. Store in cardboard boxes or mesh bags filled with vermiculite or peat moss at 40 to 50 degrees for the winter. In spring, plant the entire clump or separate the rhizomes, leaving a portion of the old stem attached to each one.
Bring Annual Geraniums Indoors
You can keep geraniums growing and blooming indoors by cutting them back by about a third and then starting to fertilize them a couple of weeks later. Keep plants in a sunny window. Or to keep them dormant for the winter, move the potted plants into a dark, cool (40 to 50 degrees) location. Don't water them and don't cut them back until they show new growth in spring.