1. Choose a variety of onion to grow: Onions come in many different varieties, so choose the one that is best suited for your climate and soil conditions. Some popular varieties include White Lisbon, Red Baron, and Walla Walla.
2. Prepare your soil: Onions prefer well-draining soil with a pH level between 6.0 and 6.8. Work in compost or well-rotted manure to improve soil structure and add nutrients.
3. Plant your onions: Onions can be grown from seeds, sets, or transplants. If starting from seeds, plant them indoors 8-10 weeks before the last expected frost date. If using sets or transplants, plant them in early spring as soon as the soil can be worked. Space your onions 4-6 inches apart in rows that are 12-18 inches apart.
4. Provide water and fertilizer: Onions need consistent moisture to grow well, so water them regularly. Fertilize with a nitrogen-rich fertilizer every few weeks.
5. Weed regularly: Onions do not compete well with weeds, so it’s important to keep the area around them weed-free.
6. Harvest: Onions are ready to harvest when the tops begin to yellow and fall over. Lift the onions out of the soil and allow them to dry in a warm, dry place for several days. Once dry, cut off the tops and store in a cool, dry place.

Onions can be affected by various pests and fungi, here are some common ones and treatments for them:

1. Onion Maggots: These are the larvae of the onion fly which burrow into the onion bulbs and cause rotting. Use yellow sticky traps to capture the adult onion flies, and cover the onions with floating row covers to prevent the flies from laying their eggs. Alternatively, you can apply spinosad, an organic insecticide, to the soil surface around the onions to kill the onion fly larvae.
2. Thrips: Thrips are small, slender insects that feed on the leaves and can cause scarring and distortion of the onions. Use insecticidal soap or neem oil to control thrips, or release beneficial insects like ladybugs or lacewings that feed on them.
3. Downy Mildew: Downy mildew is a fungal disease that causes yellowing and wilting of the leaves. Apply copper fungicides, such as copper sulfate, to control downy mildew. Rotate crops to avoid planting onions in the same location year after year.
4. Fusarium Basal Rot: Fusarium basal rot is a fungal disease that causes the bulbs to rot and become soft. Practice crop rotation and avoid planting onions in the same location for at least three years. Use fungicides that contain azoxystrobin or pyraclostrobin to prevent the disease.
5. Onion Smut:
6. Onion smut is a fungal disease that affects onions and other members of the Allium family. It is caused by the fungus Urocystis cepulae and can lead to reduced yields and poor-quality bulbs.
7. The fungus infects the onion plants through wounds or natural openings, such as stomata on the leaves. Once inside the plant, the fungus causes the formation of black, powdery spores that can be seen on the leaves, stems, and bulbs of infected plants. The spores can spread to healthy plants through wind, water, and contaminated soil.
8. Onion smut can be managed through cultural practices such as crop rotation, using clean seed and planting materials, and controlling weeds that can harbor the fungus. Fungicides can also be used to prevent and control the disease, but they are generally not as effective as cultural methods.

For organic alternatives, you can also try homemade remedies such as garlic or chili pepper sprays or companion planting with plants that repel pests like marigolds or basil. It’s always best to use a combination of preventative measures and treatment methods to keep pests and fungi at bay.