Growing Herbs Under Cover: How a Small Greenhouse Can Extend Your Herb Garden

There is something wonderfully satisfying about stepping outside and cutting fresh rosemary, thyme, parsley or basil just before preparing a meal. Unfortunately, for many gardeners, the herb-growing season never seems quite long enough.

A cold spring delays planting. The first autumn frost arrives while basil is still flourishing. Heavy rain can leave Mediterranean herbs sitting in wet soil, while a sudden heat wave can cause tender plants to wilt almost overnight.

A greenhouse will not eliminate every gardening problem, but even a small one can give an herb gardener considerably more control over the growing season.

You do not need a large glass greenhouse or a complicated heated growing system. A compact greenhouse, walk-in structure or even a well-positioned mini greenhouse can provide enough protection to start herbs earlier in spring, keep them producing longer in autumn and shelter valuable plants from unfavorable weather.

Why Herbs Are Particularly Well Suited to Greenhouses

Herbs are excellent greenhouse plants because most do not require enormous amounts of space.

A large tomato plant can quickly occupy an entire corner of a small greenhouse. By comparison, dozens of herbs can be grown in containers, narrow beds and shelves.

This makes it possible to create several different growing environments within a surprisingly small area.

For example:

• Basil enjoys warmth and protection from cold nights.
• Parsley tolerates cooler conditions and can continue producing surprisingly late in the season.
• Chives are hardy and easy to keep available for cutting.
• Rosemary appreciates protection from prolonged cold and excessive winter moisture.
• Thyme and oregano thrive when given plenty of light, drainage and airflow.
• Cilantro often performs better during cooler parts of the growing season than during intense summer heat.

Rather than thinking of a greenhouse simply as a hot space, it is better to think of it as a weather buffer.

It gives the gardener more control over wind, rain, frost, temperature and moisture.

Start With the Greenhouse, Not the Plants

It is tempting to choose a greenhouse based entirely on how attractive it looks in the garden. For growing herbs, however, practical details matter much more.

Before buying one, consider how you actually intend to use it.

Will it primarily be used for starting seedlings?

Do you want enough room to walk inside?

Will herbs be grown in pots on shelves or planted directly into beds?

Do you intend to overwinter tender plants?

Will the greenhouse remain in place permanently or be packed away during part of the year?

One useful starting point is to compare greenhouse kits by size, frame, glazing and construction rather than simply choosing the first greenhouse that fits your budget. Looking at these basic specifications makes it much easier to distinguish between a temporary plant shelter, a seed-starting greenhouse and a structure intended for more serious year-round use.

For most home herb gardeners, bigger is not automatically better.

A smaller greenhouse that is easy to ventilate, organize and maintain may be far more useful than a large structure that eventually becomes a storage shed for unused pots.

Make Use of Vertical Space

One of the easiest ways to increase the productivity of a small greenhouse is to grow upward.

Herbs are particularly suitable for shelving because many varieties grow happily in relatively small containers.

Upper shelves can hold sun-loving plants such as thyme, oregano and compact rosemary plants. Lower shelves can be useful for parsley, chives or newly germinated seedlings that do not need the most intense light.

Just remember that every shelf creates shade beneath it.

Instead of filling the greenhouse from floor to roof with solid shelving, leave open areas where sunlight can reach lower plants.

Removable shelves are particularly useful because the greenhouse can then change with the seasons.

In spring, it might hold dozens of small pots and seed trays.

By summer, some shelves can be removed to accommodate larger containers.

In autumn, the shelves can return as plants are moved inside for protection.

Containers Make Greenhouse Herb Gardening Easier

Growing herbs in containers gives you enormous flexibility.

Plants can be moved outdoors during pleasant weather and returned to the greenhouse when conditions deteriorate. Containers can also be rearranged according to the amount of sunlight different plants require.

They are especially useful when growing herbs with very different soil preferences.

Rosemary, thyme and oregano generally prefer excellent drainage and dislike remaining constantly wet.

Parsley and basil usually appreciate more consistent moisture.

Mint is another good candidate for a container, although for a different reason: keeping it confined prevents its enthusiastic roots from taking over the rest of the garden.

Use containers with drainage holes and avoid allowing pots to sit permanently in trays of water.

A greenhouse protects plants from rainfall, which means watering becomes entirely the gardener’s responsibility.

That sounds obvious, but it is surprisingly easy to overwater greenhouse plants.

Always check the soil rather than watering according to a rigid schedule.

Ventilation Is Just as Important as Warmth

New greenhouse gardeners frequently worry about keeping plants warm.

Once sunny weather arrives, the opposite problem can become much more important.

A greenhouse can warm rapidly when exposed to direct sunlight. Herbs that were comfortable early in the morning may be experiencing excessive heat only a few hours later.

Ventilation helps remove hot air and excess humidity.

Depending on the greenhouse, this might involve opening a door, using roof vents, installing an automatic vent opener or adding a small circulation or exhaust fan.

Air movement is also useful when many plants are crowded together.

Leaves that remain damp in still, humid conditions are much more likely to experience problems than plants surrounded by gently moving air.

Think of good greenhouse management as a balance between protection and ventilation.

The goal is not to seal plants inside a perfectly controlled box.

The greenhouse should protect them when necessary while still allowing plenty of fresh air.

Do Not Forget Summer Shade

It sounds slightly strange to add shade to a structure designed to capture sunlight, but during the hottest part of summer it can be extremely useful.

Shade cloth can reduce the intensity of the sun reaching plants, particularly during long stretches of hot weather.

This is especially helpful for tender seedlings and herbs that prefer cooler conditions.

If overheating becomes a recurring problem, it can be worth looking at greenhouse climate-control equipment, including fans, thermostats, shade cloth and monitoring equipment, rather than trying to solve everything by watering more frequently.

Extra water cannot compensate for every temperature problem.

In fact, repeatedly soaking plants during hot conditions can sometimes create an unhealthy combination of wet roots and humid air.

Use the Greenhouse to Get an Earlier Start

For many herb gardeners, one of the greatest advantages of a greenhouse comes before the outdoor gardening season has really begun.

Seeds can be started under cover while outdoor conditions remain unpredictable.

Basil is an obvious candidate because it dislikes cold weather. Starting plants ahead of the outdoor season means they can already be well established when temperatures are finally suitable for planting outside.

Parsley can also benefit from an early start because germination can be slow.

A small greenhouse can become a transition space between indoor seed starting and the open garden.

Instead of moving young plants directly from a protected windowsill into outdoor conditions, they can gradually become accustomed to brighter light and changing temperatures.

This process still requires attention. A sunny greenhouse can be much warmer during the day and significantly cooler at night.

A simple maximum/minimum thermometer can teach you a great deal about what is actually happening inside your greenhouse.

Extend the Harvest Into Autumn

Spring gets most of the attention, but autumn may be when an herb greenhouse becomes most rewarding.

A single early frost can end the season for tender herbs growing outside even though weeks of reasonably pleasant weather follow.

Moving containers under cover before that happens can provide a much longer harvest.

Basil will eventually decline as days become shorter and temperatures fall, but protecting it from those first cold nights can still provide additional harvests.

Parsley, chives and other cooler-season herbs may continue much longer.

Potted rosemary and other tender perennial herbs can also receive valuable protection from wet and freezing conditions.

The important point is to prepare before the first damaging weather arrives.

Trying to reorganize a greenhouse while carrying frost-sensitive plants around the garden after sunset is rarely enjoyable.

Can You Grow Herbs All Winter?

Possibly, but there is an important difference between protecting plants and actively growing them.

During winter, temperature is only one limitation.

Day length and light intensity decrease considerably in many climates. A greenhouse may keep a plant alive without providing enough light for rapid new growth.

That is perfectly acceptable.

Instead of expecting midsummer production in January, many gardeners use an unheated or minimally heated greenhouse simply to keep perennial herbs healthy until spring.

Where winter temperatures are severe, additional insulation or heating may be necessary for tender plants.

Before heating an entire greenhouse, however, consider whether it would be more efficient to protect only a smaller section containing the most vulnerable herbs.

Create a Greenhouse Herb Collection

Once the basic setup is working, experimenting becomes part of the fun.

Instead of growing only the familiar parsley, sage, rosemary and thyme, greenhouse protection can make it easier to experiment with herbs that might otherwise struggle in your local climate.

You might dedicate one shelf to different varieties of basil.

Another could contain scented thymes.

A collection of culinary sages can provide surprisingly different colors and textures.

You could also maintain mother plants from which cuttings are taken each year.

Over time, the greenhouse becomes more than protection from bad weather. It becomes a small herb nursery.

A Simple Greenhouse Herb Setup

You do not need a complicated system to begin.

A very practical starter setup might consist of:

• A small greenhouse with good ventilation
• Two or three shelves
• Several sizes of containers with drainage holes
• Quality potting mix
• A thermometer and hygrometer
• A small watering can
• Plant labels
• Scissors for harvesting and pruning
• Optional shade cloth for summer
• Optional fan for additional air circulation

Start with the herbs you already use frequently.

There is little advantage in filling a greenhouse with unusual plants if what you really want every evening is fresh basil and rosemary.

Let the Greenhouse Follow the Seasons

Perhaps the best way to use a greenhouse for herbs is not to demand the same thing from it throughout the year.

Its purpose can change with the seasons.

Spring: seed starting and protecting young plants.

Summer: growing heat-loving herbs and protecting plants from extreme rain or wind.

Autumn: extending the harvest and protecting tender herbs from early frost.

Winter: sheltering perennial plants and preparing for the next growing season.

That flexibility is what makes even a modest greenhouse so valuable.

A greenhouse does not replace the herb garden.

It complements it.

Plants can move between the garden, patio and greenhouse as conditions change, allowing the gardener to work with the seasons rather than being completely controlled by them.

For gardeners considering adding a protected growing space, resources such as CompareGreenhouse can also help make sense of the different greenhouse styles, construction materials and growing equipment available.

And perhaps most importantly, a greenhouse increases the number of days each year when dinner can begin with the simple pleasure of walking outside and cutting a handful of fresh herbs.