How to Plant Marigolds
To plant marigolds, start in the spring by finding a spot with well-draining soil, then weeding it and clearing away any rocks or other debris. Next, loosen the soil to a depth of 8-10 inches, and mix in some organic compost or well-aged manure. After that, wait for a relatively warm day, since cold soil can affect the growing process, and drop your seeds into the soil a few inches apart. Then, cover the seeds with ¼ inch of soil and water them regularly to keep the soil moist until the seeds sprout.
Wait until spring to start the planting process. You don't want to plant marigold seeds too early. Wait until early spring is over, and the danger of a spring frost has passed. During mid or late spring, you can begin readying the soil for planting your marigolds. Make sure the soil of the area isn’t too sandy or dry. Marigolds grow best in loamy, well-drained soil that water can travel through relatively easily. Sandy soil that traps water can stunt the growth of the plant. To test whether the garden soil is optimal for planting, dig a 12x12 inch hole that is about 18 inches (46 cm) deep. Fill it with water and let it drain, and then do it again and time how long it takes the water to drain. The water level in well-drained soil goes down about one inch per hour. Weed and clear the area. Before planting marigolds outside, you will want to weed the site you will be planting on. Also make sure to clear away any rocks or debris. This makes the site more hospitable to the marigold plants so that they can grow without interference. When you are weeding, grip the weed as close to the soil as you can. You want to try to remove the entire root section of the weed as well as the part above the ground, or else the weed will grow back. Lay down compost or manure. Before you plant marigolds, mix some organic compost or well-aged manure into the garden soil. This will improve the health of the marigolds by giving them the nutrients they need to thrive. Plant the seeds on a warm day. You want to make sure that the soil is warm on the day that you are planting the marigold seeds. Cool or cold soil can affect the growing process. Dig about 8–10 inches (20–25 cm) into the soil. Use a trowel or shovel to dig into the soil 8–10 inches (20.3–25.4 cm). Turn the soil over to break it up and to make it airy. Do this for the entire area in which you will be planting the seeds. As you are turning over the soil, make sure to break up any clumps and remove any rocks or pebbles you find. Sow them in the ground a few inches apart from each other. After you have prepared the soil, drop the marigold seeds in the soil a few inches apart from each other. You don't want to plant them too close to each other or they could interfere with each other's growth. Cover the seeds with ¼ inch of soil. Use ¼ inch of soil to cover the marigold seeds. This will ensure that the seeds aren't too exposed and will be able to grow. Do not use too much soil to cover the seeds; this will make it difficult for the fragile seedlings to poke out of the ground. Water the seeds regularly. Touch the soil with your fingertips to determine whether or not it needs watering. If it's dry, gently and carefully sprinkle the seeds with water. Continue keeping the soil moist until the seeds sprout. Wait until the start of spring to plant marigolds indoors. If you are growing marigolds indoors, you can start growing six to eight weeks before the last frost date. Because you are growing the flowers indoors, you do not need to worry about the soil being too cold for the plants, which is why you can start growing them earlier. If you are growing marigolds in a pot outdoors, you should wait until after the last frost to begin the process. Use a soilless potting mix for indoor containers. Use a pot filled with soilless/seed-starting potting mix. Soilless potting mix is made up of materials like peat and bark. You can find it at gardening stores or stores like Home Depot and Lowe's. Make sure the pot you are using has drainage holes in the bottom. This will allow water to pass through the pot naturally as it does in the ground. You may want to put a board or plate underneath the pot to catch any excess water or soil that comes out of the drainage holes. Sow the seeds a couple inches apart. Marigolds grown in containers can be planted closer together, but you want to make sure to give the seeds a couple inches of space in between them. Cover the seeds with ¼ inch of soil. Mix in a slow-acting granular fertilizer. Use about a teaspoon per plant of slow-acting granular fertilizer. This will give your marigolds the nutrients that they need to grow, and are active over a long period of time, about 8-12 weeks. Keep the temperature around 70 degrees. 70 degrees is a good temperature to aim for in your home. Check your thermostat and make sure that your marigolds are being kept around this temperature. If needed, you can buy a heating pad to put under the pot to keep it at this temperature. Also make sure that you start growing your marigolds away from direct light until germination. Place the plant in direct light once germination begins. Your marigold plant should start sprouting within 5-7 days. Once the plant has started sprouting, you will want to place it in direct light for at least 6-8 hours everyday. Either place the pot by a window if you live in a sunny climate, or put the pot under a grow lamp. If you are growing marigolds in a pot outdoors, keep them in direct sunlight. Water the marigolds occasionally. Marigolds do not generally require a lot of water, so water every few days. You want to let the soil partially dry out between watering. Too much dampness in the soil can over stimulate marigolds and isn't good for the plant. Water at the roots, and avoid getting the blooms, leaves and stems wet. Try to transplant seedlings, not full plants. Whether you are transplanting a flower from one outdoor spot to another or from a pot to a garden, it's best for the plants to transplant them when they are seedlings, and only about 2–3 inches (5–8 cm) tall. You can transplant them when they are fully bloomed, but if you can, you should transplant young plants or seedling. Make sure the soils are consistent temperatures. If the soils are drastically different temperatures, the transplant can be a shock to your plant and it may suffer. Try to make sure that the soil in the pot and the soil you are transplanting to are similar temperatures. When you are picking a spot to transplant, find one that receives a lot of sun. Prepare the soil. Just as you would do when planting seeds, dig about 6 inches (15 cm) into the soil, then turn it over and sift through it. Break up large clumps and remove any stones or rocks. Transplant the marigolds. Make a hole the size of the marigold root ball in the soil you are transplanting to. Gently remove the marigold plant, keeping some of the planting material around the roots of the plant. Place the plant in the small hole, and pat more soil around the plant. Space the marigolds 4–6 inches (10.2–15.2 cm) apart. If you are planting more than one marigold, make sure that they are spaced at least 4–6 inches (10.2–15.2 cm) apart. If you are planting a larger marigold variety, space about a foot apart. Water marigolds at the base of the plant semi-regularly. The amount you need to water marigold plants depends on your climate, but you will want to try for around once a week. Be sure not to overwater marigolds because it can weaken the plant. Aim to keep the soil moist as opposed to wet. Also be sure to water at the base instead of over the top of the plant. This could lead to mildew. In times of drought, water marigolds more consistently. Especially if you live somewhere that has a hot, dry climate, consider putting some mulch on top of the soil at the base of the plants in order to keep the soil appropriately moist. Use fertilizer about once a month. Soil that is too rich is not good for marigold plants. However, you should try to pat general purpose fertilizer around the marigold plants about once a month. Snip off dead blossoms. If you notice that your marigold plant has dead blooms or branches, snip them off with gardening shears. This will help the plant to bloom more freely, and will promote healthy growth for the rest of the plant. Stake them in windy environments. If the place you live in experiences a lot of wind, stake your plants. Take a thin stake or stick that is slightly shorter than your marigold plant and use plastic ties to loop the plant to the stake. The stake will keep the plant upright and will allow it to survive harsh weather and storms. 
Wait until spring to start the planting process. Make sure the soil of the area isn’t too sandy or dry. Weed and clear the area. Lay down compost or manure. Plant the seeds on a warm day. Dig about 8–10 inches (20–25 cm) into the soil. Sow them in the ground a few inches apart from each other. Cover the seeds with ¼ inch of soil. Water the seeds regularly. Wait until the start of spring to plant marigolds indoors. Use a soilless potting mix for indoor containers. Sow the seeds a couple inches apart. Mix in a slow-acting granular fertilizer. Keep the temperature around 70 degrees. Place the plant in direct light once germination begins. Water the marigolds occasionally. Try to transplant seedlings, not full plants. Make sure the soils are consistent temperatures. Prepare the soil. Transplant the marigolds. Space the marigolds 4–6 inches (10.2–15.2 cm) apart. Water marigolds at the base of the plant semi-regularly. Use fertilizer about once a month. Snip off dead blossoms. Stake them in windy environments. 