Overwintering Container Plants
This time of the year often brings questions on how to care for potted Agaves and other succulents. Caring for these plants is not difficult but a few general principals are important to follow. Below we outline some of these important basics to consider during the winter months.
One of the most important considerations for container succulent cultivation and one that is often neglected is air circulation. In habitat Agaves, cacti and other succulents are normally found in open spaces exposed to constant breezes and air movement and are seldom found in areas of stagnant air. In humid places like Southeastern Brazil the small bodied cacti are predominantly found on exposed cliff faces where breezes and gusty winds are a constant factor. These winds cool the plants bodies, keep the plants dry and help reduce insect infestations. Air circulation in cultivation provides the same benefits.
Greenhouses, suns rooms and other growing areas often provide much needed protection from cold and rain during the winter months but because they are mostly closed, create an area of stagnant air. In the south where we have lot of humidity this stagnant air can wreak havoc on potted succulents. On warm days and cool nights the humid air often condensates on the bodies of the succulents. This condensation set up an environment for fungi and bacteria to develop. This condensation is one of the reasons it is so difficult to grow well, certain desert species of agave like Agave havardiana, A. neomexicana and A. utahensis, in the humid south. Even when kept dry, by avoiding irrigation, the outer rings of leaves can often turn black and mushy making the plants look horrible and in more and sever cases can cause the entire plant can die. A constant flow of air provided by a simple oscillating fan helps to keep a plant’s body drier, thus disallowing fungal spore a place to take hold.
Insects like mealy bugs, aphids, scale insects, white fly etc… love stagnant air. Air movement from greenhouse heaters or household, oscillating fans reduces and often eliminates the colonization of many of the sucking insects because the moving air tends to dry out their soft bodies and is a general irritant to their happy living. Orchid growers have known about the benefits of good air circulation for their plants for a while and succulent enthusiast should recognize the benefit of proper air movement for their collections as well.
Air movement is also important for heat distribution and disbursement. In our part of Texas the temperatures during the day are normally mild enough that we open up the doors and vents of the greenhouses to allow heat to escape and close them at night. But during occasional, consistently cold periods the greenhouses are closed up tight. The air outside during these cold events can be mighty frigid and it is simply too cold to open the doors but on sunny days the temperatures inside can rise significantly and to dangerous levels. If you do not have a means of distributing and dispersing the heat you can get sun scald on plants even though it is freezing outside. Fans placed where the air flows over and through a collection helps to reduce the heat accumulation on the plants tissues and reduced the chance of heat damage.
Avoid excessive irrigation during a plants dormant period
Of course many of our favorite succulent plants occur in areas where there is a moist season and a dry season. There are the summer moist/winter dry regions with Mexico, East Cape South Africa and Northwestern Argentina. Then there are the winter moist/summer dry areas like West Cape South Africa, Chile, California, etc... Knowing where a given succulent is native to is important to know, in order to irrigate properly during winter months. Most agave and Cacti come for the summer moist/ winter dry scenario and it is best to avoid excessive winter irrigation. We normally recommend that Agaves, cacti etc should not be watered much in the winter. What is “not much” you say? Well you have to assess the situation day by day. If you have a prolonged cold spell you should certainly not water your plants because cacti, hate cold, wet roots. In out part of Texas we can have many warm (even hot) winter days and some irrigation dose not hurt them and an occasional dose of water can be beneficial. It all depends on the species of course. Trial and error, and research help determine how one should proceed but if the temperatures are warm we water our succulents about twice a month or on a wet to dry cycle, with the dry period being the longer of the two. If you are in a consistently cold region you may not want to water your potted collection at all during a plants dormant period
We avoid fertilization of succulents in the fall and winter, especially for outside cultivated plants because this might stimulate tender growth on a plant that should be dormant when cold arrives. We want to also avoid fertilization on inside cultivated plants also, so they are not stimulated to grow when light conditions are not optimal and any resulting growth may develop in a less than optimal and spindly manner.
Even with proper air circulation and optimal irrigation insect infestations occur. The worst problem we have on Agave, in the winter, is mealy bugs and the biggest problem for cacti can be scale. In the summer when a plant can take lots of moisture a good blast of water from the water hose is sufficient for the control of mealy bugs. But in the winter when you do not want to over water your plants, dousing a plant with a jet of cold water is not an option. To control all of the soft bodied insects in the winter we use a variation of the following formula sprayed on with a pump up sprayer. On occasion we will change up the formula and substitute or add Neem Oil and or a small amount of Orange Oil to the Ultra Fine Horticultural oil base so the formula is not always the same.
Per Gallon of Water
- 1 oz of Ultra Fine Horticultural Oil
- 2 oz of Spinodad
- 1 oz of Pyrethrum
Repotting in the winter
Though cacti want to be left alone and should not be repotted going into their winter rest Agaves tend to do fine if transplanted to larger pots or divided in the fall. In the South the moderate temperature of fall seem to stimulate some root growth on most agave and allows a transplanted plant time to establish sufficient roots before winter dormancy. We would not recommend repotting agaves during the dead of winter unless you have bottom heat but if you have moderate fall temps, fall transplanting seems to works just fine. It is recommended however that you do not oversize the pot you transplant into during this time of year. If you transplant into too large of a container and the soil gets too cold and wet for a period, the chance of rot increases. For example a 4” pot agave can easily go into a 6” pot or gallon at this time but we would avoid attempting to pot it into a 5 gallon container. Note: An exception to repotting agave in the fall would be to avoid repotting the forms of Agave victoria-reginae or A. ferdnanadi-regis in the fall.