Here's how to plant herbs outdoors
Herbs are some of the easiest plants to grow because they tolerate a variety of soil types and have relatively few insect and disease pests. Herbs can be incorporated into any garden, planted in spaces between shrubs and trees, or be grown formally in a garden of their own.
Select the herbs to be grown based on the light exposure of the site they will be planted in. This information can be found on seed packets or plant labels. For example, chervil (Anthriscus cerefolium) grows best in full shade, thyme (Thymus spp.) will grow well in partial shade to full sun, and sage (Salvia officinalis) grows best in full sun.
It is best to plant herbs in soil with good drainage. If water remains pooled on the top of the soil several hours after watering or a rain event, then the soil drainage is poor and should be amended to improve water infiltration.
To correct this problem, remove the top 12 inches of soil from the area that will be planted in the early spring prior to planting. Mix peat, horticultural sand, vermiculite, and-or compost in with the soil, backfill the area and then level the soil.
This is also a good time to remove any weeds from the soil. Removing the entire weed, including the roots, will prevent weeds from vegetatively propagating.
Herbs should be planted based on the recommendations on the seed packet or plant label. Seeds and transplants are commonly purchased at garden centers. When purchasing transplants, pick plants free of insect and disease pests and that look healthy. It is difficult to impossible to improve plant quality.
Some herbs do not transplant well and should be directly sown from seed. These include: anise (Pimpinella anisum), chervil (Anthriscus cerefolium), dill (Anethum graveolens), cilantro-coriander (Coriandrum sativum), cumin (Cuminum cyminum), parsley (Petroselinum crispum), fennel (Foeniculum vulgare), caraway (Carum carvi), and borage (Borago officinalis).
When planting, space herbs according to the recommendations on seed packets or plant labels. Proper spacing will facilitate optimal plant growth. Avoid overcrowding because it can lead to favorable environments for insect and disease pests.
Label the herbs individually or at the end of a row as a reminder of what was planted. A good trick is to cover the seed packet with plastic (plastic wrap or baggies work well) and staple it to a wooden stake or use the ready-made plant label that came with the purchased plant.
Herbs do not require large amounts of fertilizer and will lose flavor when over-fertilized. Fertilization should be based on soil test recommendations. Stop fertilizing perennial plants when fall temperatures are around freezing.
Fertilizing promotes plant growth, which can make the plant vulnerable to damage or death from cold winter temperatures. Check soil moisture using a trowel, moisture meter, or your fingers and irrigate when the soil is dry a few inches below ground. When needed, irrigate until the top six to eight inches of the soil are moist. Avoid over-irrigation, as herb flavor may be negatively affected.
Several perennial herbs will benefit from division including: tarragon (Artemisia dracunculus), sweet woodruff (Galium odoratum), horehound (Marrubium vulgare), oregano (Origanum spp.), chives (Allium spp.), lovage (Levisticum spp.), mints (Mentha spp.), lavender (Lavandula spp.), and thyme (Thymus spp.).
Divide herbs in early spring or fall when the plant becomes too large or the center dies, usually every two to four years. Use a shovel to cut the plant into sections taking as much root as possible. Sections can be replanted in new locations.
Be sure to water the sections after replanting to aid in establishment. The woody or dead center of the plant can be removed and placed in a compost pile.
The cold temperatures of winter may damage or kill some perennial herbs. Mulching at least four inches deep at the base of the plant can increase soil temperatures enough to prevent cold damage to the herb roots. Good sources of mulch include bark chips, straw, and leaves.
For answers to your garden questions, call the Lehigh County Cooperative Extension Office, 610-391-9840, or Northampton County Cooperative Extension Office, 610-746-1970, and ask to speak with a Master Gardener. Volunteers staff phone lines several days a week, Monday - Friday.
Growing Green is contributed by Lehigh County Cooperative Extension Office Staff and Master Gardeners.