Hi Guys,

The Winter holiday season is almost here and with that brings the cold temperatures, frost and snow and short winter days and long winter nights.

One of the biggest challenges cactus growers have is getting their cactus/cacti through these dark and cold winter months, in this Blog/Article I will be sharing my tips and tricks on how you keep your cactus ALIVE over the winter.

KNOW YOUR CACTUS

The most important thing is to know what type of cactus you have, this is really important because many different varieties of cacti are more cold tolerant when it comes to their minimum temperatures than others, where Desert cacti need to be kept dry with little or no watering over Winter, most of the Rainforest cacti will still need to be watered over the winter months especially the winter flowering species like Schlumbergera, ( Christmas & Thanksgiving Cacti ) and some of the Winter flowering Rhipsalis Cacti.

There are two main groups of cactus, the Rainforest Cacti and the Desert Cacti. Rainforest cacti are cacti that grow in Rainforests in Central and South and North America and look very difference in appearance to the Desert group of cacti ( See photo above ) these cacti grow on trees as Epiphytes and have flattened segments that are modified leaves, these Epiphytic cacti need more moisture and often more winter warmth than many of the Desert group of cacti do, examples of Rainforest cacti would be Schlumbergera, commonly known as Christmas and Thanksgiving cactus and the Rhipsalis group and Epiphyllum group.

Desert Cacti are cacti that have adapted to survive in hot and dry and arid conditions. Desert cacti grow in the dry arid regions of Central, South and North America and well and the Southwestern U.S, they store water in their thick stems to survive long periods of drought. Many of these cacti can tolerate cold temperatures if kept absolutely dry during winter due to their natural habitats dropping as low as -15c /5F during the night.

However there are some Tropical Desert cacti that definitely do need more winter warmth over winter especially the cacti that are from Brazil, such as Melocactus, Uebelmannia, Pilosocereus.

Once you know what type/s of Cacti you grow this will help you with how to provide the right care for your cacti over the winter months.

Some Tropical Cacti such as this Uebelmannia above are not cold hardy and need a winter minimum temperature of 10c /50F, very different to many Desert cacti that can tolerate much colder temperatures.

TEMPERATURE

Many cacti can survive cold winter temperatures but ONLY if they are kept dry with no water given to them from mid September until early to mid April, this is an absolute must because cacti have a winter dormancy period during this time, watering cacti when they are dormant may cause cacti to rot, their roots and soil needs to be dry during their winter dormancy, and the drier the cactus is kept the more chances the cactus has of surviving the cold winter months.

The minimum safe winter temperature to overwinter your cacti would be 5c /41F.

I keep my cold hardy Desert cacti in the polytunnel at an absolute winter minimum of 5c /41F, this is the overall safe winter minimum temperature for all of the cold hardy varieties for the types of cacti that I grow, but if you live in a dry arid desert climate then many cacti can tolerate lower temperatures than this especially when kept dry, but I keep my polytunnel at an absolute minimum of 5c /41F due to the fact that I live in Ireland where the humidity is always high ( I will be talking about humidity in this Article too )

I use a special electric heater by Biogreen that is for greenhouses and polytunnels, it has a special thermostat setting that sets the heater to come on if the temperature inside the polytunnel drops below 5c /41F this keeps the air temperature inside my polytunnel at a minimum of 5-6c /41 44F making it safe for my cacti over the cold winter months.

My Cacti are kept at a minimum temperature of 5c /41F with a Biogreen electric greenhouse heater with a thermostat setting.

Please note that there are some succulents that look very ‘Cactus alike’ such as the Euphorbia group, many newcomers to the hobby will easily mistake a Euphorbia for a cactus due to their ‘cactus looky likey’ appearance to them, but most Euphorbia are not cold hardy and will need a winter temperature of at 10c /50F. If you are unsure of what cactus/cacti you have its best to be on the safe side and bring them indoors for winter.

WATERING

Desert cacti naturally have a rest period and go into dormancy over the winter months, its important to stop watering completely from mid September until early to mid April, this is important even if you overwinter your cacti indoors in the house in room temperatures, this is because once the daylight levels begin to fall from Fall/ Autumn cacti enter their winter dormancy period, and by late Fall /Autumn cacti will be in their dormancy rest period, watering cacti when they are dormant may result in rot due to the cactus resting and not needing water during this stage, the only time you can give your cacti a light watering in winter is if you have them indoors and they are clearly showing signs of too much shrivelling, this is often the case during the later part of the winter such as late January/Feb/March, there are times I will give my cacti that I overwinter indoors for winter a light watering late winter if they start too show too much shrivelling. I have made a video for my You Tube Channel called Desert Plants of Avalon on ‘Should you water your Cactus in Winter’ and I explain in a lot more detail in that video and if you want to know more then please go and watch the video below:

Rainforest cacti like the Schlumbergera ( Christmas & Thanksgiving Cacti ) and Rhipsalis are epiphytic and don’t need a winter dormancy like the Desert cacti do, the Epiphytic cacti especially the Schlumbergera that are winter flowering do still need to be watered regularly over winter, but I do cut back on giving as much water to my Schlumbergeras once they have finished flowering from late December /early January, and with my other Epiphytic cacti like my Rhipsalis I will give a light watering once a month, my Epiphyllums aka ‘Orchid Cacti’ I overwinter cool in my polytunnel at 5c/41F because Epiphyllums do flower better with a cool and drier winter rest than the other Epiphytes like Schlumbergera and Rhipsalis, and because of this I keep my Epiphyllums ‘Orchid Cacti’ more on the drier side than my Schlumbergera and Rhipsalis over winter, but I do give my Epiphyllums a light watering over winter once every 6 -8 weeks just enough watering to prevent their hanging long stems from shrivelling too much.

My Epiphyllum ‘Orchid Cacti’ I overwinter more on the drier and cool side compared to my other Epiphytic cacti such as my Schlumbergera and Rhipsalis, but I do still give my Epiphyllums a very light watering once every 6-8 weeks in winter just enough water to prevent their hanging stems from shrivelling too much.

LIGHT

A lot of growers often worry about the lack of light over the winter for their cacti especially as many growers have to move their cacti indoors for winter to protect them from cold and rain if they don’t have a greenhouse or other protective structure to overwinter their cacti in, but the good news is when cacti are resting over winter then light is not a necessity, I know many growers who overwinter their cacti in dark rooms, garages, cellars, and basements with very little or even no light and they overwinter their cacti with no problems and have done this for years, however I personally have had no experience of this myself, but as cacti are dormant over the winter rest period I can see no problems with overwintering cacti in low light levels as long as the temperature is kept cool ( below 15c / 60F ) and they are kept absolutely dry with no watering at all, as low light and warm temperatures and not being kept dry at their roots can encourage problems such as etiolation ( thin stretched out growth ) as well as rot issues. If you do overwinter cacti in low or very little light over the winter months then its extremely important that when you move your cacti back out to their Spring and Summer positions that you acclimatise them to the higher light levels very slowly, moving cacti from dark positions into a bright sunny position will result in your cactus getting scorched and scarred from the higher light levels even if you don’t move them directly out into the sun. Cover your cacti with a few layers of sun shade cloth, you can use garden plant fleece cover for this, cover the cacti loosely to still allow air to the cacti and keep your cacti away from the heat of the sun for the first 10 days, remove a layer of fleece cover every 3 days to slowly acclimatise your cacti to receiving more light, by the end of the 10 days your cacti will have acclimatised to the higher light levels of the outside.

I overwinter my cold hardy cacti that can take 5c /41F in my polytunnel that is light and bright, but my non cold hardy cacti I move indoors for winter and I overwinter these in my Grow Room, I do use special LED Grow lights in the corners of the room where there are no windows to give my cacti a boost of light over the winter, and although this is not a necessity when cacti are dormant in winter I personally find the additional grow lights in winter help to boost the cacti for producing buds and flowers the following spring, if you do have a bright and ideally a sunny position to overwinter your cacti in winter such as a sunny window, greenhouse or sun room/ conservatory then this will help to boost your chances of getting more flowers in the spring and summer, but if you only have a dark position to overwinter your cacti it does not mean you won’t still see flowers on your cacti in the spring and summer, I know plenty of growers who get lots of flowers on their cacti in spring and summer who overwinter their cacti cool and dark in basements, garages, cellars, sheds etc.

DAMP & HUMIDITY

Believe it or not its not the cold that is the biggest challenge for cacti in winter but the damp and humidity that is a problem for cacti in winter especially if you live in a climate that has high humidity such as the U.K or Ireland. I live in Ireland and the humidity is always high here, during the summer its not an issue when the cacti are actively growing, but in winter high air humidity can cause damp and black spots and even base and stem rot on dormant cacti, indoors this is rarely a problem especially with indoor air being drier due to central heating in winter, but for cacti that are in greenhouses, polytunnels, unheated sun rooms/conservatories, sheds etc then high humidity can be a killer for cacti, the best way to deal with this is to open up doors, windows, vents on the dry and cool winter days to ventilate and change the air as much as possible, use large circulating fans in greenhouses etc to keep the air circulating on the days its too cold or windy or wet to open up doors, I always try to open up the polytunnel door by half a metre for at least 4 hours a day on the days its not too wet and windy to circulate the air inside my polytunnel as much as possible, its the cold stagnant non moving air that is the biggest challenge for cacti, a large circulating fan is ideal to have on for a few hours each day if doors cannot be opened, there are also special dehumidifiers that are made especially for cold rooms such as basements, sheds and greenhouses, I have a dehumidifier especially for my polytunnel that works well at low temperatures, I use one by ProBreeze and have it on a few hours during the days it is exceptionally wet and it helps to lower the inside air humidity inside of my polytunnel to about 50%, they can however be expensive to run if used daily and because of this I alternate between using a circulating fan which is very economical and opening the polytunnel door on the non windy days as much as possible.

PESTS & DISEASES

Those annoying ‘Beasties’ like Mealy Bugs, Spider Mites, Scale insects are always around even in the winter, but they do slow down during their activity during the colder months of winter if cacti are overwintered cool in greenhouses, polytunnels etc, but indoors in winter when the central heating radiators are on encourages ‘beasties’ to still attack cacti, Mealy bugs and especially Spider mites love the dry warm air of indoors and when cacti are dormant they are less resistant to pests, its very important to be extra vigilant with pests on cacti during winter, any signs of pests should be dealt with as soon as possible, use a tiny brush or q tip dipped in rubbing alcohol to remove any Mealy bugs and their woolly nests and any scale insects can be rubbed off with a brush and rubbing alcohol, but Spider mites and are not as easy to get rid of during winter when cacti need to be kept dry, normally I love to use Horticultural Neem oil in spring and summer to spray the cacti both to prevent and treat any signs of spider mites etc as its a natural pesticide, but during winter I don’t like to use Neem oil as I find it impossible to use without some of the Neem oil solution wetting the soil, so during winter I have to use the chemical method instead and use ‘Bug Clear Ultra 2’ concentrate on any spider mites I see because this dries fast on the cacti and does not tend to wet the soil, I also use Diatomaceous earth dusted on all the cacti both indoors and in the polytunnel as this will also help to slow down and prevent those annoying little ‘Beasts’ from attacking your beloved cacti.

The most common diseases of cacti in winter is basal and stem rot, molds and virus’s, its not the cold itself but the combination of the cold and damp and wet that causes these problems, wet and cold dormant cacti are a recipe for cactus death, even watering a dormant cactus indoors in a warm position can sometimes cause rot issues because the cactus is dormant and will not be taking up water via its roots, keeping your cactus dry and making sure the air circulation in greenhouses, sheds, sun rooms, conservatories etc is ventilated regularly as mentioned before with doors, vents, windows circulating fans etc is a fantastic prevention for molds, rots and other issues, also making sure your cacti are protected from frost and protected from any night temperatures that fall below 5c /41F.

I hope you enjoyed reading this Article and got some tips and tricks on How to keep your Cactus ALIVE over Winter.

I have made a video for my You Tube Channel called Desert Plants of Avalon on ‘How to keep your Cactus ALIVE over Winter’ and you can watch this video below.

Wishing you all a wonderful Happy Holiday Season and New Year Cactus Powered 2025 and Thank you for your continued love and support throughout 2024.

LOVE and HAPPINESS and PLANT POWER ALWAYS.

Lyn.