Easy. Pinch off all flowers and buds.
Some plants are self fertilizing, it's difficult to do that.
Pick off all the flowers when they appear.
Depends on what type of plants you have.
Just cut off the seed pods before they are mature.
Mix water with some corn starch and spray it over the plant. It wont kill the plant but stop it of producing flowers and seeds.
or trow some cornmeal over the plants... it will do the same!
According to your update that you want to prevent dandelion from producing seeds without killing them, generally, you need to get rid of their flowers while you mow the lawn.
Yip
As the dandelions begin to bloom pick off the flowers immediately and put them in the trash. The plants will not set seeds and will not spread.
Pinch off all of the flowers.
The problem is most plants also spread by various methods of roots separating out to new plants. You'll end up with more and more dandelions anyways.
Unless you intend to grow dandelions as a crop (they are nutritious when not poisoned) you need to kill them.
Pick all the flowers off the plant before they can develop seeds.
You do not have to cut the flowers. Just cut off the seed pods before they mature.
Rose hips hold seeds. Mallow is called cheese plant because its seed pods look like little round cheeses. Most poppies have pods which when dries, their tiny seeds pour out of tiny holes on top of the pod. Sweet pea holds seeds in long pods, and when the pod is dry, it pops open shooting the seeds all over.
Depends on the plant, if it is self fertilizing, difficult to do that. If it requires another plant to fertilize it (male and female plants) then removal of one of those will reduce seed production. If you have issues with seedlings under a plant or shrub that is a perennial, you can use a product that prevents seeds from sprouting- like Preen or even Crabgrass and Weed preventer.
Depends on what type of plant. If it flowers then you would remove the flowers. If it is a fruit tree or vegetable plant you can protect from pollination, either from insects like bees or from other plants that would be seeded pollinators
Why would you want to keep the dandelion alive or thriving? There can't be too many of you around, and (sorry, but there shouldn't be). Do you also like crab grass?
Aside from my rudeness. I have heard of people using boiled water, or steam. But it will ALWAYS come back, especially if you, or neighborhood leave other dandelions go to seed.
*How do you stop a tomato plant from producing tomatoes without killing it? You pinch of it's buds.
(You can't keep up with all the dandelions)
