GrowGuides > Growing Tender Plants Outside

Overcome frost and cold spells with a little ingenuity

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 high tunnels or year-round sunshine but there are still plenty of ways to produce an excellent harvest of these valuable crops.

Common tender plants:

• Sweet peppers
• Hot peppers
• Eggplant
• Tomatoes (except for some outdoor varieties)
• Cucumbers (except for some outdoor varieties)
• Melons

Tender young plants

Vegetables like the above, and others, 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. Other examples that need initial protection are:

• Sweet corn
• Squash such as zucchini
• Tomatoes (outdoor varieties)
• Cucumbers (outdoor varieties)
• Pole beans
• Bush beans

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 drainage is 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

Not every gardener has the luxury of a greenhouse in which to start off their vegetable crops, and it is possible to manage without. You might have a sunroom or an enclosed porch – as long as your seedlings get plenty of light, any of these options are ideal. Window sills are also fine places for raising seedlings, but be aware that your potting soil should never be allowed to dry out (especially if your plants are situated above a radiator).

Small seeds (such as those for tomatoes) can be sown thinly into trays of damp potting soil, which are then covered with plastic or glass covers, until the seedlings emerge.

Bigger seeds (such as those for beans and eggplant) can be planted individually into 10 cm pots. These 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, you need to prick out the little plants into individual 12cm pots (as many as you require), selecting healthy-looking seedlings.  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 acclimatizing your plants. This is known as hardening off (see below) and is particularly important for tender plants.

Hardening off

First, check that the daytime temperature outside is 60ºF, or higher. If it is, place your pot of seedlings in a sheltered area in the garden. But remember to bring inside the pot when the temperature becomes cool at night. Gradually, over three weeks or so, you can extend the period of time you leave your pot of seedlings outside, before bringing it 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-paneled 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 (see above).

You can buy a cold frame made from timber and plastic or you can create your own by covering a wooden box with a solid sheet of plastic or glass.  It will need to have a hinged or sliding lid so you can open it for ventilation.

Row Covers

Row Covers are transparent protective structures, often in the shape of a small tunnel.  Most modern row covers are made from plastic or polythene sheet. The advantage of using a row cover rather than a cold frame, is that a row cover can be moved to where your plants are situated, to provide them with protection.

You can extend the growing season by several weeks by using a row cover to warm the soil before sowing and planting. Place the row cover over the prepared soil and leave it in place for about a month before you need to plant out your vegetables.

Row covers come in a variety of shapes and sizes, so it’s worth doing some research and deciding on the type that suits you best. Look out for the following features:

• Stability – flimsy plastic row covers can blow away, become distorted and tear easily.
• Size – you need to ensure that your row covers are wide and tall enough for your crops so they don’t touch the sides.
• Ease of access for watering since the row cover also prevents rain reaching the plants.

Ventilation. Although you should be able to close the end of your row covers, it is important to allow some air to circulate to prevent disease and stop your plants wilting from heat on a clear sunny day.

Note: You can make your own row covers using wire hoops and plastic sheeting.

Fleece

Large sheets of fleece can be spread over your vegetable garden to warm the soil, weighted 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.

Bubble wrap

Bubble wrap traps bubbles of air and, as a result, is an excellent insulator. It can be used in many ways to protect the plants in your garden.

• It can be used like fleece, to warm your soil.
• It can be layered over plants to protect them from the frost
• It can be used in sheets to insulate windows or unheated greenhouses.

Mulching

Some protection can be provided by layering straw and other mulches around established plants. But wrap them in fleece if a really sharp frost is forecast.  Mulches can nourish the soil as well, but may make the perfect hiding place for slugs or other pests.

Providing shelter

Spending a little time evaluating your site can be very worthwhile when working out how to provide the best protection for your plants.

• South facing areas are ideal because the longer sun-exposure warms them up.
• A house wall can 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.
• Trellis fencing, outbuildings or hedges offer protection from the wind.

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.

Summary

• Tender plants must be protected from the damaging effects of cold winds and frost.
• Some plants are best grown indoors or under cover in cooler climates.
• Many plants need to be sown indoors or under cover but can then be ‘hardened off’, before being planted outside.
• You can protect plants outside by using cold frames, row covers, fleece and bubble wrap.

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