Sowing seeds in your garden beds are cheap and cost-effective. Some seeds can be sown directly in the garden beds, and some will require a start in seedling trays and then transplanted out into the garden.
Always read the instructions on the seed packet or ask at your local garden shop or nursery. The instructions will advise you on whether you can grow in situ or start seed germination in seed trays and then transplant.
Easy Annual Flower Seeds For Spring/Summer Garden
If you have a short summer season, it would be best to start your seed growing indoors and transplanted once all chance of frost has passed.
Sunflowers

Some of the tallest varieties get to six feet (2 meters) or more. There are two types of sunflowers - the single head and the multi-head.
The single-headed sunflower only produces one giant flower on the plant. Once it dies, the plant will die.
The multi-headed sunflower produces smaller multi flower heads and can be deadheaded to make another bloom or two.
Sow your seeds directly after all frost has passed and the soil has warmed. The taller varieties might need staking, especially if you are in a windy area.
Sunflowers have a deep root system and will grow in just about any type of soil.
Water sunflowers at least once a week or earlier if the soil is very dry in hot weather.
African Marigolds

They are also called American Marigold or Aztec Marigold.
Marigold is very easy to grow from seed. They self-seed, and there is an enormous amount of seeds you can collect for the next growing season.
The seeds are big and easy to scatter on a prepared garden bed. They can be started in seed trays, but I usually sow them directly in the garden beds in spring. Keep deadheading, and they will bloom all summer long.
Sweet Peas

Look for the winter-flowering variety if you are in a warm area.
Soak the seeds overnight before sowing.
Sow seeds in trays from late February in good quality germination soil. After 2 to 3 weeks, you will see the seeds germinating.
By mid-April, the transplants will be ready for the garden or pot near a trellis or tee-pee.
Plant in a well drained site with lots of added compost.
Pinch out the central growing tip to encourage lateral growth for a healthier bushier plant.
Give them a good soak and feed with organic fertilizer every second week.
Flowers should show by mid-July, and remember to pick them often and deadhead to encourage more flowers.
Nasturtiums

Nasturtiums are not fussy about soil and will grow in just about any soil in the summer. They can be perennial in the warmer zones.
Seeds can be soaked overnight before sowing. Sow the seeds directly in the garden in full sun once the soil temperature has reached 50F (10C). Or earlier indoors if you have a very short summer season.
There are many varieties, dwarfs and trailing varieties and a multitude of colors to choose from.
Deadhead them water regularly.
Nasturtiums will attract aphids under the leaves. Some vegetable gardeners plant them as a trap crop to encourage the aphids away from the vegetables.
Besides the aphids, there are not a lot of problems with nasturtiums.
The seeds look like a caper when growing on the plant, and they self seed well.
All of the plant, the flowers and leaves are edible.
Petunias

There are different varieties of petunia, ranging from large blooms called Grandiflora. Those with smaller blooms but numerous flowers called Multiflora. Milliflora produces masses of flowers on mini plants. And lastly, Wave Petunias are the trailing or spreading variety.
Sow petunia seeds in a growing medium indoors 10-12 weeks before planting outdoors. They will germinate in 7-10 days.
Petunias love the sunlight. Transplant out in the garden once they have 3-4 true flowers. Water regularly in containers, but those in the garden bed will require less watering.
Space them about 1.5 feet (45cm) apart in the garden bed.
Deadhead often to encourage more flowers.
Zinnia

Zinnia can be planted in a sunny position directly into the soil once frost has passed.
Moisten the soil and place the seed on the ground. Lightly cover with soil. Push down slightly with your hand or an implement.
Water gently so as not to wash away the seeds and keep the soil moist but not soggy, until germination. Over-watering is just as harmful as under-watering. Germination will occur between 7-10 days.
Once the plants have established, let the soil dry out between watering.
Morning Glory

Morning Glory can be sown directly into the garden bed once the weather has warmed in spring.
Soak the seed in water overnight and cover them with soil.
Morning Glory is a climber, so plant them near a fence. Morning Glories grow quickly and love the full sun.
Easy Annual Flower Seeds For Winter Garden
Choose cool-season annuals for a lovely display that will bring cheer to your garden in the winter months.
Primula Malacoides (Fairy Primula)

This primula variety is very easy to grow from seed and enjoys the winter climate above 28F (-2C) and partial shade.
Start the seeds in trays in June or July and plant out into the garden or in pots once they have 2 or 3 sets of true leaves. Barely cover the seeds with the germination mix as they need light to germinate.
Fairy Primula prefers partial sun and rich soil and does not like to dry out, so keep the soil moist.
Feed the Primulas every second week until flowering has finished
Calendula (Pot Marigold)

Calendula seeds can be sown outdoors, directly in the ground in cold climates. They are easy to germinate and simple to care for.
Calendula is edible and medicinal and enjoys cooler temperatures. Although I have had success with them in full sun on my deck area, which gets warm 64F (18C) during the winter days.
Calendula self-seed readily, and you can collect some to plant the next season.
Poppy

Poppy seeds can be sown directly into the soil in cold areas as they do not mind the cold.
There are various poppies such as Iceland Poppys, Papaver or Corn Poppy, Flanders Poppy ((Memorial Day), plus many more.
Mix the seed with sand, as this makes it easier to see the ground you have covered. Sprinkle the tiny seeds thinly on a windless day, press the seeds in by stepping on the soil, or use a wood plank. Keep the soil well-watered.
Once they germinate, add a light layer of mulch. Keep the seedlings moist until they are well established.
Butterflies and bees will arrive once the poppies start to flower.
Deadhead and remove some of the dead stems from time to time.
Collect the seedpods once the flower is spent. The poppies will probably reseed in the fall.
Pansies and Viola

Early spring and late fall plantings - depending on your climate. A mild winter area can enjoy pansies all year long. Pansies enjoy a cool climate and grow best when temperatures are below 68F (20C).
Pansies come in almost every color, from white to nearly black.
Pansies can be planted directly into your garden bed or started in seed trays indoors - depending on your climate.
Cover the seeds with soil as they germinate in darkness. Keep the soil moist but not soggy.
Thin out after they have two or three leaves. Keep them watered until they are well established.
Pansies will flower profusely if they are deadheaded regularly.
Cosmos

Cosmos is one of the easiest of the annual flowers to grow from seed even in poor soil. They may be considered a perennial in warm zones 9 and 10.
Cosmos thrive in full sun but will do well with a bit of shade. They do not require any fertilizer as this will decrease the flowers and increase the foliage.
Sprinkle the seeds over the ground and press down lightly to make contact with the soil. Water well until germination then sparingly after that.
There are different varieties - tall and short varieties. Plant in spring, and they will bloom from early summer to the first frosts.
Almost no other flower will give you such a bumper crop.
Deadhead or pick for the vase at least once a week to promote more buds. Harvest the seeds for next season's planting. They do self-seed, which means they will come up again next season.
Use one of the dwarf varieties if you are planting in containers.

Takeaways
Most annuals grow easily from seed. Read the instructions on the seed packet for instructions for your region.
Some annuals self-seed, so remember to shake the plant over the garden bed when it is time to pull them out. New plants will grow next year.
Save your seeds and swap with your gardening friends for a wider variety.