When To Cover Basil Plants

You should cover basil plants when the temperature is expected to drop below 50°F (10°C) at night.

Basil is a tender herb that simply cannot handle cold, and even a light frost will turn those beautiful green leaves into black, mushy messes.

However, knowing when to cover basil plants isn’t just about frost warnings, it’s also about those chilly late summer evenings and sudden cold snaps that sneak up on you.

In this post, we’ll explore the exact temperatures that trigger the need to cover basil plants, how to use row covers and cloches effectively, and the signs that tell you it’s time to take action.

Let’s dig in.
 

When To Cover Basil Plants: The Temperature Rule

The simplest answer for when to cover basil plants is to start paying attention once nighttime temperatures dip into the 50s.

Basil thrives in warmth, and its ideal growing range is between 80°F and 90°F during the day.

When the mercury starts to fall, the plant’s metabolism slows down, and it becomes vulnerable to chilling injury.

Here’s the breakdown of temperatures that matter:

1. Cover Basil Plants Below 50°F (10°C)

This is your first warning sign that you need to cover basil plants.

At this temperature, the plant isn’t in immediate danger of dying, but its growth will stall completely.

The leaves may start to show slight discoloration or a droopy appearance.

If you want to extend your harvest, this is the time to throw a cover over them for the night.

2. Cover Basil Plants Below 40°F (4°C)

Once the forecast calls for temperatures in the 30s, covering basil plants becomes absolutely critical.

At this point, frost is highly likely, and frost will kill basil very quickly.

The water inside the plant’s cells begins to freeze, which destroys the cell walls and turns the leaves to mush.

You should cover basil plants with a frost blanket, old sheet, or even a cardboard box if this is your only option.

3. Cover Basil Plants When Frost Is in the Forecast

Even if the temperature reads 36°F, a light frost can form on clear, calm nights.

This is why you should get into the habit of checking your local weather forecast every evening during the shoulder seasons.

If the meteorologist mentions “patchy frost” or “frost advisory,” that’s your cue to cover basil plants without delay.

Don’t wait until you see frost on the grass in the morning, because by then, it’s usually too late.

How To Properly Cover Basil Plants

Covering basil plants isn’t complicated, but there are a few techniques that work better than others.

The goal is to trap heat from the soil and create a microclimate that’s a few degrees warmer than the outside air.

Here’s how to do it effectively:

1. Use Floating Row Covers

Floating row covers are the gold standard for protecting basil.

These lightweight fabrics allow sunlight and water to pass through while trapping heat.

You can drape them directly over your basil plants, but make sure they extend to the ground.

Secure the edges with rocks or soil so the wind doesn’t blow them off.

You can leave row covers on for several days at a time, even during sunny days.

2. Use Cloches or Plastic Bottles

For individual basil plants, a simple cloche works wonders.

You can use a glass jar, a plastic milk jug with the bottom cut off, or a store-bought bell cloche.

Place the cloche over the plant in the late afternoon so it can trap the day’s heat.

Make sure to remove the cloche during the day if temperatures rise above 60°F, or you’ll cook your basil.

3. Water the Soil Before Covering

Here’s a pro tip: water your basil deeply in the afternoon before you plan to cover it.

Wet soil holds heat much better than dry soil.

As the water evaporates overnight, it releases warmth that can protect your basil plants from a light frost.

Just be careful not to soak the leaves themselves, as wet foliage can promote fungal diseases.

When To Remove The Covers From Basil Plants

Knowing when to cover basil plants is only half the battle.

You also need to know when to take the covers off so you don’t suffocate or overheat your herbs.

The general rule is to remove covers as soon as the sun comes up and temperatures start climbing.

1. Remove Covers in the Morning

As soon as the morning sun hits your garden and temperatures rise above 50°F, take the covers off.

If you leave them on during a warm day, the trapped heat can become excessive and stress the plants.

Aim to uncover your basil by mid-morning at the latest.

2. Keep Covers on for Extended Cold Spells

If you’re experiencing a prolonged cold front with multiple nights in the 30s, leave the covers on for several days straight.

Row covers are breathable, so they won’t harm the plants if left on for a week or more.

For plastic cloches, you’ll need to vent them during sunny afternoons to prevent condensation buildup.

Signs That Basil Needs Covering

Sometimes, the weather forecast is wrong, and you get a surprise cold snap.

You need to learn the visual cues that signal your basil is stressed from cold.

Look for these signs, and you’ll know you should have covered basil plants sooner:

1. Dark, Water-Soaked Spots

When basil experiences chilling injury, the leaves develop dark, translucent patches.

These spots look like they’ve been bruised and will eventually turn black.

If you see this, the damage is already done, but you can still cover basil plants to protect the healthy leaves.

2. Wilting Leaves

If your basil looks droopy even though the soil is moist, cold stress is likely the culprit.

The cold makes it hard for the roots to take up water, causing the leaves to lose turgor pressure.

This is a clear indicator that you need to cover basil plants immediately.

3. Leaf Drop

When basil gets too cold, it will start shedding its lower leaves as a survival mechanism.

If you notice leaves falling off overnight, that’s a huge red flag.

Your basil is telling you it’s freezing, so cover it up fast.

So, When Should You Cover Basil Plants?

You should cover basil plants whenever the nighttime temperature drops below 50°F, but especially when frost is predicted.

Basil can’t survive freezing temperatures, and even a mild frost will kill it.

Start covering basil plants in early fall or late spring when the nights get chilly.

Make sure to use breathable row covers or cloches to protect them from the cold.

And always remember to remove the covers during the day so they don’t overheat.

By following these timing tips, you can keep your basil plants productive well into the cooler months and enjoy fresh leaves for much longer.