How to Sow

Mint may be grown from seed sown early indoors and transplanted outside after frost, or planted as a potted plant.

Sowing Seed Indoors:

• Sow mint seeds indoors 8-10 weeks before the last frost in spring using a seed starting kit.
• Sow seeds ¼ inches deep in seed-starting formula.
• Keep the soil moist at 70 degrees F
• Seedlings emerge in 7-14 days
• As soon as seedlings emerge, provide plenty of light on a sunny windowsill or grow seedlings 3-4 inches beneath fluorescent plant lights turned on 16 hours per day, off for 8 hours at night. Raise the lights as the plants grow taller. Incandescent bulbs will not work for this process because they will get too hot. Most plants require a dark period to grow, do not leave lights on for 24 hours.
• Seedlings do not need much fertilizer, feed when they are 3-4 weeks old using a starter solution (half strength of a complete indoor houseplant food) according to manufacturer’s directions.
• If you are growing in small cells, you may need to transplant the seedlings to 3 or 4 inch pots when seedlings have at least 3 pairs of leaves before transplanting to the garden so they have enough room to develop strong roots.
• Before planting in the garden, seedling plants need to be “hardened off”. Accustom young plants to outdoor conditions by moving them to a sheltered place outside for a week. Be sure to protect them from wind and hot sun at first. If frost threatens at night, cover or bring containers indoors, then take them out again in the morning. This hardening off process toughens the plant’s cell structure and reduces transplant shock and scalding.

Planting in the Garden:

• Select a location (out of the way or in a container due to rapid spread) in full sun or part shade with good rich, evenly moist soil. Consider that mints can be vigorous spreaders and may be best grown in containers or raised beds.
• Prepare the bed by turning the soil under to a depth of 8 inches. Level with a rake to remove clumps of grass and stones.
• Dig a hole for each plant large enough to amply accommodate the root ball.
• Carefully remove the plant from its pot and gently loosen the root ball with your hands to encourage good root development.
• Set the plants 18 inches apart. Or plant in containers in a commercial potting mix.
• Place the top of the root ball even with the level of the surrounding soil. Fill with soil to the top of the root ball. Press soil down firmly with your hand.
• Use the plant tag as a location marker.
• Thoroughly water and apply a light mulch layer on top of the soil (1-2 inches) to conserve water and reduce weeds.

How to Grow

• Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their seeds from germinating. 
• Mulches also help retain soil moisture and maintain even soil temperatures. For herbs, an organic mulch of aged bark or shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time. Always keep mulches off a plant’s stems to prevent possible rot.
• Keep plants well-watered during the growing season, especially during dry spells. Plants need about 1 inch of rain per week during the growing season. Use a rain gauge to check to see if you need to add water. It’s best to water with a drip or trickle system that delivers water at low pressure at the soil level. If you water with overhead sprinklers, water early in the day so the foliage has time to dry off before evening, to minimize disease problems. Keep the soil moist but not saturated.
• To encourage a flush of new growth, cut the stems back to the ground after the plants flower.
• To propagate, divide the plants in spring or fall.
• Monitor for pests and diseases. Check with your local Cooperative Extension Service for pest controls recommended for your area.

Growing Tips

• Harvest leaves as needed. Right before flowering cut stems one inch from the ground. After cutting plants back you can get a second harvest the same season. 
• Fresh or dried, spearmint, peppermint, and apple mint leaves make a healthful and delicious tea. Add the fresh leaves and flowers to salads and desserts.
• Mint may be dried or frozen or preserved in vinegars. Mint is great for jams and jellies.

Common Disease Problems

Anthracnose: Small water soaked spots on leaves and stems. Burpee Recommends: Avoid planting in the same location in the future, planting in containers can help. Prune plants to the ground in the fall.

Damping Off: This is one of the most common problems when starting plants from seed. The seedling emerges and appears healthy; then it suddenly wilts and dies for no obvious reason. Damping off is caused by a fungus that is active when there is abundant moisture and soils and air temperatures are above 68 degrees F. Typically, this indicates that the soil is too wet or contains high amounts of nitrogen fertilizer. Burpee Recommends: Keep seedlings moist but do not overwater; avoid over-fertilizing your seedlings; thin out seedlings to avoid overcrowding; make sure the plants are getting good air circulation; if you plant in containers, thoroughly wash them in soapy water and rinse in a ten per cent bleach solution after use.

Mint Rust: Small, whitish, slightly raised spots that turn reddish orange or brown. This occurs on the underside of the leaves. Burpee Recommends: Avoid overhead irrigation systems. Water early so the leaves have the whole day to dry out. Do not plant members of the mint family in the same location.

Powdery Mildew: This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. Burpee Recommends: Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning. Contact your Cooperative Extension Service for fungicide recommendations.

Verticillium Wilt: Yellows begin turning yellow starting at the margin. Eventually, leaves will curl and die. Burpee Recommends: Rotate plantings, remove infected plants, do not over fertilize.

Common Pest and Cultural Problems

Aphids: Greenish, red, black or peach colored sucking insects that can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.

Cutworms: These insects cut off the seedlings at the soil level. Burpee Recommends: Place a paper cup collar (use a coffee cup with the bottom cut out) around the base of the plant. They are usually mostly a problem with young seedlings. You can also control by handpicking and controlling weeds, where they lay their eggs.

Flea Beetles: These small hopping beetles feed on plant foliage and spread diseases. Burpee Recommends: Rotate crops with plants in a different plant family. Use floating row covers to prevent damage to young foliage.

Spider Mites: These tiny spider-like pests are about the size of a grain of pepper. They may be red, black, brown or yellow. They suck on the plant juices removing chlorophyll and injecting toxins which cause white dots on the foliage. There is often webbing visible on the plant. They cause the foliage to turn yellow and become dry and stippled. They multiply quickly and thrive in dry conditions. Burpee Recommends: Spider mites may be controlled with a forceful spray every other day. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for miticide recommendations.

Thrips: Thrips are tiny needle-thin insects that are black or straw colored. They suck the juices of plants and attack flower petals, leaves and stems. The plant will have a stippling, discolored flecking or silvering of the leaf surface. Thrips can spread many diseases from plant to plant. Burpee Recommends: Many thrips may be repelled by sheets of aluminum foil spread between rows of plants. Remove weeds from the bed and remove debris from the bed after frost. Check with your Cooperative Extension Service for pest controls.

FAQ

Can I grow mint indoors during the winter? Yes mint is fine for indoor growing, as long as you have plenty of light.

How can I prevent my mint from spreading throughout the garden? It is best to contain it somehow, either by planting in containers or raised beds, or sinking a barrier around the plant in the soil.

How can mint be used as a companion plant? Mint can be planted as a companion to plants in the cabbage family as it can deter pests. It can benefit carrots as it deters carrot root fly. It is good to plant with onions, radishes and tomatoes as it deters insects that attack those plants. Mint also repels fleas, flies and ants.

Is mint easy to grow from seed? Mint can actually be challenging to grow from seed, but is extremely easy to grow from plants.

I brought my mint plant indoors and all the leaves are drying up. What happened? It is possible that the plant is experiencing transplant shock from the very different outdoor and indoor growing conditions. Try to acclimate your plants slowly when bringing them inside or outside at the changing of seasons. Indoor conditions are usually much drier that outdoor so keep the humidity level higher by placing your container on a tray of pebbles. Also make sure your plants are getting sufficient light as light conditions tend to be weaker indoors. For the plant you have, try cutting back any dead growth and it may grow from the stems or roots.