Thyme in Zone 5A — Midwest

Thyme is a fantastic addition to any Midwest herb garden. Its aromatic leaves bring a savory flavor to everything from roasted vegetables to hearty soups, which are staples during our long winters. Plus, it's a perennial, so you'll enjoy it year after year.

We know our Midwest weather can be unpredictable, with temperature swings in the spring and summer heat spells. But with a little attention to timing, you can easily grow thyme within our 157-day growing season.

Starting thyme indoors gives you a head start, especially since it can be slow to get going from seed. You can start seeds indoors from late February through mid March, about eight weeks before you'll want to transplant. Use seed trays and provide warmth, either with a heat mat or by placing them in a warm spot.

Bottom watering is key to prevent damping off; just set the tray in a shallow dish of water and let the soil absorb it. Keep in mind, with our moderate-to-late springs, it's sometimes easier to simply buy starts from a local nursery.

Transplant your thyme outdoors from early to late May, once the danger of frost has passed. Be sure to harden off your seedlings for about a week before transplanting, gradually exposing them to outdoor conditions. Space them 8-12 inches apart in a sunny spot.

Keep an eye on the weather forecast during this time – we sometimes get a late frost that can nip young plants. Buying established starts from a local grower is a great option, saving you a whole season of waiting for your thyme to mature.

Direct sowing thyme is also an option. Sow seeds outdoors from early May through mid July. The soil needs to be warm enough for germination, so waiting until after any potential late frosts is best.

Prepare your soil by loosening it and removing any weeds. Sow the seeds thinly, spacing them 8-12 inches apart. Direct sowing can be a bit less reliable than transplanting, but it's a simple way to grow thyme if you're patient.

Thyme is very drought-tolerant and thrives in well-drained soil, which is great considering our humid Midwest summers. Overwatering is a quick way to cause root rot, so be cautious. During the spring, when rainfall is more frequent, you might not need to water at all unless we're experiencing a dry spell.

During our moderate-to-hot summer heat spells, check the soil moisture using the finger test: stick your finger about two inches deep into the soil. If it feels dry, it's time to water. Generally, an inch of water per week, including rainfall, is sufficient. Water at the base of the plant rather than overhead to minimize fungal issues in our moderate-to-humid climate.

Yellowing leaves can indicate overwatering, while wilting leaves signal underwatering. Applying a light layer of mulch around the base of the plant can help retain moisture without suffocating the roots.

Thyme requires minimal pruning. After flowering, usually in mid-summer, cut back the stems by about one-third to prevent the plant from becoming woody. Avoid cutting into the old, woody growth, as it may not regrow.

This encourages new, bushier growth and keeps the plant productive. As first frost approaches in early October, you can give it one last trim to tidy it up for winter.

You can start harvesting thyme as early as early July, about 70 days after planting, and continue through mid October. The best flavor comes just before the plant flowers. Look for healthy, vibrant sprigs.

To harvest, simply cut the stems, then strip the leaves. Regular harvesting encourages the plant to produce more growth, so don't be shy! As first frost approaches in early October, harvest as much as you need and dry or freeze the excess for use throughout the winter.

Thyme is generally easy to grow, but there are a couple of common problems we see here in the Midwest.

Root Rot from Overwatering

• What it looks like: Yellowing leaves, wilting even when the soil is moist, and a general decline in the plant's health. The roots will appear brown and mushy instead of white and firm.
• What causes it: Overwatering, especially in our wet-summer climate, can lead to root rot. Heavy clay soil that doesn't drain well exacerbates the problem.
• How to fix/prevent it: Ensure your thyme is planted in well-draining soil. Water only when the top two inches of soil are dry. Consider planting in raised beds or containers to improve drainage. Avoid overhead watering to reduce soil moisture.

Fungal Diseases in Humidity

• What it looks like: Powdery mildew (white, powdery spots on leaves) or leaf spot (small, dark spots).
• What causes it: High humidity, especially after rainfall, creates an ideal environment for fungal diseases. Poor air circulation around the plants also contributes.
• How to fix/prevent it: Ensure good air circulation by spacing plants properly. Water at the base of the plant to avoid wetting the foliage. Apply a fungicide if necessary, following label instructions.

Midwest Specific Challenges: Our moderate-to-hot heat, moderate-to-humid humidity, and wet-summer rainfall can create conditions that favor both root rot and fungal diseases. Careful monitoring of soil moisture and good air circulation are essential for healthy thyme.

Thyme makes a great companion plant in the Midwest garden. It grows well with rosemary, sage, and lavender, as they all prefer similar dry, sunny conditions. Thyme also benefits cabbage and strawberries by deterring pests. It's a good friend to tomatoes, too, as it can improve their flavor and repel certain insects.

Avoid planting thyme near mint, as mint is very aggressive and can quickly take over the space, crowding out the thyme.