Growing Tender Plants Outside

, written by Katherine Benzinski gb flag

Tomatoes ripening

Many of the most worthwhile vegetables you can grow at home are classed as ‘tender plants.’ Although they can be grown successfully in cooler climates they will not survive outside in cold weather without some form of protection. You may not have the luxury of heated polytunnels or year-round sunshine but there are still plenty of ways to produce an excellent harvest of these valuable crops.

Tender young plants

Tender plants such as sweet peppers (capsicum), hot peppers, aubergines, tomatoes, cucumbers and melons need to be started off early under cover to give them a long growing season. Then they can be planted out in the garden when the conditions have warmed up.

Know your site

You need to be aware of the limitations of your own garden – factors such as position, soil type and climate. If they are not suitable, you might have to artificially create the ideal conditions for your plants. To grow well, plants require warmth and shelter.


Know your enemy

Low temperature (both of the soil and the air). A tender plant’s greatest enemy is frost. Very cold weather causes water in plant cells to freeze, which causes damage to the cell wall. The plant goes limp and will very rapidly turn brown and die.

Exposure to cold or strong winds can be equally damaging. The traditional walled garden provides the perfect setting for growing crops, but a hedge or a line of shrubs can also offer shelter and warmth during the winter months.

Poor drainageis another killer of tender plants, as their roots will rot in waterlogged soil. Heavy clay soils can remain cold long into spring.

Starting plants off inside

If you don’t have the luxury of a greenhouse in which to start off vegetable crops, a conservatory, sunroom, porch or even a windowsill is suitable as long as your seedlings get plenty of light. Be aware that your compost should never be allowed to dry out, especially if your plants are situated above a radiator.

Bigger seeds (such as beans and aubergines) can be planted individually into 10cm (4in) pots. They can be watered gently and then covered with plastic film to help the germination process.

Read the seed packet instructions carefully for each variety of vegetable you grow and follow the instructions about how deep to sow the seeds and how long the seeds will take to germinate.

Potting up

Once your seedlings are growing healthily and are large enough to handle, prick them out into individual pots. This should always be done by holding the leaf of the seedling, not the stem, and gently easing the roots out using a teaspoon or similar implement. You can then continue to grow your seedlings inside.

Supposing you have chosen a ‘hardy’ type of tomato that, eventually, you want to grow outside, then you need to wait until the risk of frost has passed. Also, you need to begin the process of acclimatising your plants. This is known as ‘hardening off’ and is particularly important for tender plants.

Hardening off vegetable seedlings

Hardening off

First, make sure that the daytime temperature outside is 16ºC or higher, and if so, move your pot of seedlings in a sheltered area in the garden. Remember to bring the pot inside when the temperature becomes cool at night. Gradually, over three weeks or so, you can extend the period of time you leave your seedlings outside, before bringing them back indoors, from about three hours a day to all day.

Another way of doing this is to use a cold frame. This is a clear-panelled box with a lid that can be opened or closed to allow temperature control. The glass (or plastic) top should stand open during the day (for varying periods, as above), but make sure that it is closed up at night to protect the seedlings from the colder temperatures. At the end of this process, your plants should be ready for planting in your vegetable plot.

Starting plants off outside

Cold frames

A cold frame retains heat and protects plants from the wind, so it can be used to raise early seedlings or to harden off plants that have been started indoors. You can buy a cold frame made from timber and plastic or you can make your own by covering a wooden box with a solid sheet of plastic or glass. It will need a hinged or sliding lid so you can open it for ventilation.

Cold frame


Cloches are transparent protective structures, often in the shape of a low tunnel. Cloches can be easily moved to where your plants are situated to provide them with protection. You can extend the growing season by several weeks by using a cloche to warm the soil for about a month before sowing and planting your vegetables.

Cloches come in a variety of shapes and sizes, so it’s worth doing some research and deciding on the type that suits you best. Make sure it is stable enough, big enough and easy enough to open up for watering, weeding and ventilation.

You can also make your own cloches using wire hoops and plastic sheeting.


Large sheets of fleece can be spread over your vegetable garden to warm the soil, weighed down at the edges to prevent them blowing away. Once you have sown your seed, the fleece can be put back in place to protect the emerging seedlings and it will lift as the plants grow, without damaging them.

Fleece has the added advantage of allowing some moisture through so that there is less of a requirement to water underneath.


Bubblewrap traps bubbles of air and so is an excellent insulator. It can be used to warm your soil, like fleece, or you can layer it over plants to protect them from the frost. You can also use sheets of bubblewrap to insulate cold frames or unheated greenhouses.


Some protection can be provided by layering straw and other mulches around established plants. Mulches can nourish the soil as well, but may make the perfect hiding place for slugs or other pests.

Providing shelter

Spend a little time evaluating your site to work out how to provide the best protection for your plants.

South facing areas are ideal because the longer sun-exposure warms them up. Trellis fencing, outbuildings or hedges offer protection from the wind. A house wall can also provide protection from winds and also absorb warmth from the sun, which is reflected back on your plants. At night, warmth from the house can also protect against mild frosts.

If you want to grow tender fruit, such as peaches or apricots, then you will need to use a combination of the techniques described above. Train them up a warm wall and cover them with fleece over the winter and early spring to protect them from frost damage.

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"Cabbage worms and eggs, squash bug eggs. lots of small slugs damaging cauliflower, squash, and raddish leaves."
Queenie Kravitz on Sunday 2 July 2023

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