Yard and garden: Growing herbs in the home garden

Iowa State University Extension
Basil

AMES, Iowa — Herbs are annuals, biennials and perennials that die back to the ground each year and are used for their flavor, fragrance and medicinal properties.

These easy-to-grow plants not only provide new and different flavors and aromas to food but can be beautiful additions to the landscape. Aaron Steil, consumer horticulture specialist with Iowa State University Extension and Outreach, answers some frequently asked questions on growing herbs at home. 

What herbs are best to grow in Iowa?

There are dozens of different species and varieties of herbs that can be grown, but a few are particularly easy to grow in Iowa.

  • Basil is an annual started easily from seed each spring.
  • Cilantro is grown as an annual. The fresh leaves are known as cilantro and the seed is called coriander.
  • Dill is an annual famously used for pickles, but plants also serve as a food source for the caterpillars of swallowtail butterflies.
  • Parsley is a biennial often grown as an annual that comes in both curly and flat-leaved varieties. Mint is a spreading perennial that needs to be planted in a place where its spreading nature can be contained.
  • Chives are a clump-forming perennial with beautiful flowers and tasty leaves.
  • Thyme is a low-growing, spreading perennial perfect for the small spaces in the front of the garden.
  • Oregano is a perennial that is both a beautiful addition to the garden and a wonderful flavoring in a Mexican or Italian dish. 

What growing conditions do herbs need?

Herbs grow best in the same conditions as most vegetables. Plant in full sun with at least six hours of sunlight a day. While not ideal, some species will grow in part-sun, receiving two to four hours of direct sunlight each day.

Herbs will grow well under a wide range of soil conditions, with the exception of extremely wet, poorly drained soils. Provide well-drained conditions where soils are allowed to dry out slightly between waterings. In general, herbs do better in soils with low to medium fertility, so additional fertilizer applications are not typically needed. Too much fertilizer produces lots of foliage that is low in flavor. 

Perennial herbs should be grown in an area where they will not be disturbed year to year. They overwinter best when soils are well-drained and do not stay wet over the winter months.

Some marginally hardy species in Iowa, like sage and lavender, sometimes benefit from an extra mulch layer applied just after the soil freezes in November and removed by mid-March. Annual herbs can be grown in a vegetable garden or any full-sun, well-drained location that allows for easy harvest and use.

How do I harvest herbs?

Most herbs can be cut and used fresh throughout the growing season. They can also be harvested, dried and stored for use during the winter months.

Many herbs, such as sage, rosemary and basil, are grown for their leaves. These herbs should be harvested when their flower buds are just beginning to open. The oils in the leaves which give each herb its distinctive flavor and aroma are at their maximum levels at this stage of growth.

Remove approximately one-third of the current year's growth on perennial herbs. Annual herbs can be cut back more severely. Make the cuts on annuals approximately 4 to 6 inches above the soil surface. The annuals can be cut at ground level when harvesting in the fall before the first frost. Most annual and perennial herbs can be harvested in mid-summer and again in the fall.

Herbs should be harvested in the early morning, after the dew has evaporated but before the sun becomes hot. After harvesting, rinse the herbs in cool water. Shake off excess water and place them on paper towels to dry for a few minutes.

How do I dry herbs for later use?

Air drying is the most popular method to dry herbs. To dry whole branches or stems, gather eight to 12 stems in a bunch. Tie the ends of the stems together and hang each bunch upside down in a warm (70 to 80 degree Fahrenheit), dark, well-ventilated location. The herbs should be dry in two to four weeks.

When thoroughly dry, strip the leaves from the plants. Crush or crumble the leaves and store in airtight jars in a cool, dry place.

Another way to dry herbs is to place them on a drying tray. A simple drying tray consists of fine mesh screen or cheesecloth attached to a wooden frame. A small window screen also works well. Place wooden blocks under the corners of the drying tray to insure good air circulation. Place a single layer of leaves or stems on the drying surface and keep the herbs in a warm, dry area until they are thoroughly dry.

A gas or electric oven can also be used to dry herbs. To oven dry, spread a layer of leaves or stems on a cookie sheet or shallow baking pan. Place the herbs in a warm (up to 180 degree) oven for three to four hours. Leave the oven door open and stir the herbs periodically until they are thoroughly dry.

Some herbs, such as dill, caraway, and coriander, are valued for their seeds. Harvest the seedheads just before they turn brown. Cut off the entire seedhead and place it in a paper bag. Then place the bags in a warm, dry location. After drying, shake the seeds loose in the bag. Remove any chaff by pouring the seeds from one container to another outdoors in a light wind.

Can I grow herbs indoors over the winter?

Many herbs can be successfully grown indoors during the winter months. The best herbs to grow indoors include basil, cilantro, parsley, chervil, rosemary, bay laurel, mint, chives, oregano, thyme, sage and lemongrass.

Light is often the most limiting factor when growing herbs indoors. Ideally, plants receive four to six hours of direct sunlight a day. Some species, like parsley, mint and chives, will tolerate a little less light. Others, like rosemary, thyme and bay laurel may need supplemental light from a full-spectrum LED or florescent grow light. Put the grow light on a timer for 12 to 16 hours a day. If long, lanky growth is noticed, more light may be needed.

Plant herbs in containers with a well-drained potting soil. Clay or terracotta containers work particularly well for herbs because they are more porous, allowing the potting mix to dry well between waterings. Plastic and ceramic containers, as well as hanging baskets and window boxes, are all good options as well. Be sure the container has sufficient drainage holes in the bottom. 

The water requirements vary depending on the species of herb being grown, but all should be watered when the potting soil is dry to the touch and before the plant begins to wilt. Although herbs do not require as much fertilizer as other plants, they will benefit from periodic light fertilization with a balanced, all-purpose fertilizer at half or quarter strength.

Annual herbs can be grown by seed throughout the winter months. Stagger seedings to always have new plants ready to harvest. Perennial herbs can be overwintered indoors but should be moved outdoors in late spring when temperatures warm up.