The first step in planting sweet pea flowers is typically choosing an appropriate location. Sweet peas tend to grow best in sunny spots, although partial shade is also acceptable. After you have selected a location, you will need to get the soil ready. Some compost or manure worked into the dirt to a depth of at least 1 foot (30 cm) will help to improve the soil quality, which should give you a better chance of having flowers that thrive. You will eventually need some stakes or a trellis because sweet pea flowers are climbers, but you can wait until the flowers start to get taller before putting these in place.
If you are planting sweet pea flowers from seed, you will likely benefit from nicking the seeds first and letting them soak in lukewarm water for about 12 hours. This should help them germinate faster once they are in the ground. Bury your sweet pea seeds in the soil of your desired planting location to a depth of about 1 inch (2.5 cm), and space additional seeds apart by no more than 3 inches (7 cm). If you plant them too close together, there is a slight risk of mildew development. You will also need to water the area thoroughly right after planting.
Once your sweet pea flowers are well established, caring for them shouldn't be very difficult. These flowers normally need lots of water, so it will probably be important to make sure the soil doesn't get too dry in between watering times. You should also be careful not to over-water the flowers. The ideal soil for sweet peas is typically moist, but not soaking wet. They might need even more water than usual when the weather is very hot and dry for weeks at a time, and they usually do not survive when temperatures exceed 80 degrees Fahrenheit (26 degrees Celsius).
It is not always necessary to fertilize sweet pea flowers, but it might be a good idea if your soil is of poor quality. You can do it either once a month, or you could opt to use a slow-release fertilizer when you initially plant the flowers so they are fed continuously. You should also try to keep dead or wilted flowers off the plant. If you pick the dead blooms off and discard them as soon as you notice them, it may stretch out the length of time your sweet peas will bloom for the season.