Hollyhock seed can be planted in either spring or fall. In areas where the winters are severe (like here), more plants will survive if seeds are planted in the spring and the seedlings have the entire growing season to settle in. I think it’s interesting that when I let my hollyhocks reseed naturally (or when I scatter seed in the fall), most of the seeds won’t germinate until the next spring. It would probably be different in an area with warmer temperatures, but I always wait until spring to plant any seeds I have purchased. Hollyhock seeds can be planted outside about a week before the last frost. Plant the seeds one-quarter to one-half inch deep and keep them well-watered but not wet. Most hollyhock seeds will germinate in less than two weeks.
It is always a good idea to prepare the soil and let it rest for at least a couple of days before planting. Hollyhocks grow best in a good, rich soil that is slightly acid to alkaline. For the biggest and most colorful flowers hollyhocks should be grown in an area that receives at least six hours of sun every day, and they should be mulched and watered frequently to keep the soil moist.
When I start seedlings indoors, I plant two seeds about a quarter-inch deep in a two-ounce cup. If both seeds germinate, I transplant one seedling to a second cup. I continue transplanting periodically to larger cups until the seedlings grow large enough for a six-inch pot. (I sterilize and reuse the same cups… and pots… year after year.) If you have young hollyhock seedlings to transplant, wait until all danger of frost is past and the soil temperature is at least 50°F.
I have read that the ideal spacing for hollyhock plants is twelve to twenty-four inches apart in rows at least three feet apart. I have always planted hollyhocks much closer than that, and if I broadcast the dried seed in the fall, I just scatter the seed around the existing hollyhock stalks. I have never had any problems with mildew or the hollyhocks not growing well or not flowering profusely, but perhaps I have just been lucky.
Most hollyhocks will produce leaves the first year and flowers and seeds the second year. Some hollyhocks will die after this two-year cycle, but I have found that cutting the stalks down to the ground each fall (leaving a couple of inches of stalk so I can see where each plant was growing) and adding a heavy layer of compost will keep most of the hollyhocks growing and flowering for several more years. I don’t cut the stalks until I have harvested the seed heads, and I leave the seed heads on the plant as long as the approaching freezing temperatures permit.