The days are getting shorter and colder. Now is the time to prepare your garden for the first frosts – before it is too late! Frost occurs when water vapour in the air forms dew and is then cooled to the point of freezing. This usually occurs at night and may be patchy depending on the landscape. Cold air is heavier than warm air, so any depression or low-lying area in the ground can allow the chill to pool and collect like an invisible puddle or ‘frost pocket’.
North facing slopes have the sun blocked for most of the day, especially in the winter. They are the last to feel the touch of the sun’s warmth. The dew wants to settle on these gardens in particular.
The ideal conditions for creating frost include clear night skies, calm winds, and temperatures below 2.5° Celsius. All airborne water (life fog) is future frost waiting for the temperature to drop
Frost can be a killer, whereas snow is a natural frost protector that gently covers plants and stops the ground from freezing.
The most common ways that we protect our plants from frost in the garden are greenhouses, plastic tunnels, straw, cold frames, and a frost blanket also called horticultural fleece. When you cover your plants, you need to make sure that you uncover them by midmorning, to allow the sun to warm the plants and the soil, and to cover them again when the sun is off the garden. Insulating plants from the warmth of the sun will do more harm than good!
Not all plants respond to frost in the same way. Some plants that bring welcome colour and form to the winter garden are hardy. This means that when temperatures drop below freezing, the leaves, stems and roots cope with the lower temperature and stay alive, whether they are in the ground or in a pot. Taking time and effort to protect them is not needed, especially when other plants need more care.
However, many of the other species that we have been enjoying all summer, quickly freeze and die when it gets too cold outside, and they need you to protect them before the first frosts. You can save your plants and keep them happy and healthy throughout the season if you follow these guidelines. Then, when the weather warms up next spring, and the plants have had a good winter’s rest, they can go back outside for the new growing season. A little diligence now will save you money as you won’t need to spend money replacing them.
Mulching
The best time for mulching the flower border is late autumn, before the soil hardens with the frost. The mulch should be about 4” (10cm) thick to protect the roots and crown buds from the frost. Your worms will have plenty to eat all winter and will do all the work necessary in your winter garden, by increasing the depth of your topsoil, while you stay warm inside!
Alternatively, you can put on a layer of straw. This can be left in the garden as a weed supressing mulch for the spring.
Summer Bulbs
Summer Bulbs like Dahlia Tubers, Canna Lilies, Gladioli can be removed from the flower border once the greenery has died down towards the end of the autumn. They need to be lifted, put into a box with a blanket or fleece for insulation and stored in a frost free shed or garage until it is time to replant them in the late spring.
Remember to make a note on the calendar to check them for signs of rot. Any that are affected should be thrown away so as not to affect the rest.
Vegetable Patch
A layer of fleece on the vegetable patch can be effective at keeping the frost away, so long as it has been put on before the first frost. If you missed it, you will be keeping the ground colder for longer as the insulation works both ways – the cold will be trapped in!
The fleece may be lifted on warm sunny days, (or put on for the first time) but don’t forget to replace it before the sun goes down!
Place plants in the greenhouse, cold frame, or conservatory
Our wonderful patio planters may not withstand the cold, as the water within the soil freezes, so they will need protection if they are to survive the winter.
If you don’t have a greenhouse, you can buy a mini greenhouse quite cheaply to save your plants. The protection of even these modest greenhouses will keep the overnight temperatures as much as 5°C warmer than outside. This is enough to keep plants frost free unless it is an extremely cold snap. Then, you may consider to wrapping horticultural fleece over the plants or you may prefer to bring the plant into the conservatory.
Just stand the potted plants off the ground using pot feet to raise them up inside the greenhouse.
Allow the compost/soil to dry out so that the roots remain dry throughout the cold, dormant period. They will revive again, with water in the spring.
Use your house walls to your advantage.
If you don’t have a greenhouse, another way to protect your containers is to huddle them altogether against a sheltered wall of your house. A little of the heating from inside warms the walls just a little, but a few degrees maybe enough to make a difference in temperature for your plants.
The pots should be lifted off the ground with pot feet to ensure good drainage. The pots may be wrapped in bubble wrap, sacking or even thick newspaper to keep them warmer. However, the compost should not be covered, as the rain will need to be able to drain away.
The wall itself offers support on windy days.
Succulents
These need to go under cover too. Succulents store water in their leaves. If the frost turns the water into ice, the cell walls breakdown in the same way as strawberries in the freezer. Once they defrost, the cell walls cannot repair, and the leaves turn to mush.
Tender Plants
You need to look after your tender plants, e.g., bedding plants and hanging baskets, and keep them indoors until after the first frost. Locally, here in Cheltenham, it is recommended not to plant out summer bedding until the end of May Bank Holiday. Then all the risks of frosts have passed. They will need to go out slowly to ‘harden off’ which is what we call the transition to the change in their environment.
Tropical Plants
Many tropical plants, such as banana palms and cordylines will need extra protection from frost. You can make a fleece jacket packed with straw to protect the crown. Water must not collect at the base of the stems, as this causes the plant to rot. A thick mulch will protect their roots.