Cactus Care – Page 2 – Gardener Report

The reason for Christmas cactus not blooming is because of drought stress or too many hours of light, as it is a short day plant. Christmas cactus are adapted to rainforests with high humidity and rainfall. It does not flower if its dry or there are too many hours of light during flower formation. There are several other factors that can prevent Christmas cactus (Schlumbergera) flowering which I have summarized here: Conditions:Reasons for Christmas Cactus not Blooming:Underwatering and low humidity.Christmas cactus is native to rainforest and prefers more moisture and humidity the other cacti to promote flowering.Too many hours of light.Christmas cactus is a short day plant and requires at least 12 hours of darkness for 6 weeks from around September to form flower buds.Large pots or containers.Larger pots encourage root development rather the displaying flowers. Christmas cactus prefers its root system to be somewhat pot bound to promote flowering.Wrong temperature.Optimal growing temperature is around 68°F (20°C) but a temperature during the hours of darkness of around 60°F (15°C) is preferred for the development of flower buds.Too much moisture around the roots.Saturated soil causes moisture stress and root rot which prevents flowering.Too much sun.Christmas cactus prefers indirect right light. Full sun can burn the plant.Too much fertilizer.Feeding the cactus whilst flower buds are developing reduces flowering. Keep reading for why your Christmas cactus is not flowering and for the best practices and how to implement solutions so that it can display flowers... 1. Under Watering and Low Humidity Christmas cactus is a plant that is native to the tropical rainforests of Brazil where it grows in hot and humid conditions with relatively high rainfall, and whilst shaded by the canopy of trees. This is in stark contrast to most cacti species which grow in hot sandy deserts with low humidity, infrequent rainfall and have several adaptations to cope with drought. When people hear the word 'cactus' when referring to Christmas cactus, the associations with the desert dwelling species causes people to assume that Christmas cactus does not need much watering when the opposite is true. Drought stress prevents Christmas Cactus from flowering. If the cactus is underwatered, the soil dries out too quickly and the humidity is too low Christmas cactus does not flower due to drought stress. This is a mistake that I personally made and my cactus did not flower properly until I recreated some of the conditions of the cactus native environment with higher levels of humidity and watering more often. To encourage a Christmas cactus to bloom... Water your Christmas cactus more often. Typically watering once per week provides your cactus with the optimal balance of moisture to meet the water requirements without causing root rot so that the cactus can bloom without any undue moisture stress. Spray the cactus with mist regularly, particularly if you live in an arid climate. Houses tend to be lower in humidity anyway compared to outdoors and much lower then rainforests, so regularly misting is essential to create a humid micro-climate to slow water loss from the leaves and recreate the plants ideal conditions. Spray the leaves at least once a week in temperate climates and 2 or 3 times a week in dry climates for best results. Water the cactus with a generous soak. Watering too lightly causes the water to not infiltrate the soil properly and the moisture does not reach the roots causing drought stress which prevents flowering. Another potential problem when it comes to underwatering is if the cactus is planted in potting soil that contains peat as peat repels water off the surface when it dries out. This can prevent water infiltrating the soil properly and the roots are not able to uptake the moisture they require. If the potting soil repels moisture then submerge the soil in a basin of water for 10 minutes to ensure that water can absorb properly to reach the roots or replant the cactus in more porous soil amended with horticultural sand or grit. With regular watering and higher levels of localized humidity due to spraying mist on the leaves to emulate the natural environment, the Christmas cactus has a better chance of blooming in your home. (Read my article to learn how often and how much to water your Christmas cactus according to your climate and conditions). 2. Christmas Cactus Requires at least 12 Hours of Darkness to Flower Christmas cactus flowering. Christmas cactus is rather unusual in that it is a 'short day plant' which means requires at least 12 hours or more of unbroken darkness to form flower buds. If the 12 hours or more darkness is interrupted by turning on lights in the middle of the night then this can interfere with the development of the cacti flower buds and prevent it from flowering. This is due to the Christmas cactus being adapted to sense seasonal change by detecting change in the hours of daylight to initiate the formation of flower buds. Most plants detect a seasonal change in temperature which then promotes the formation of flower buds, whereas Christmas Cactus relies on both day length and temperature change in its native environment of the rainforest to stimulate the formation of flower buds and signal the right time for flowering. To promote blooms at around Christmas time ensure that you cactus is in a room that stays dark at night as even turning a bright light on for a few minutes can interfere with the development of flowering. One potential solution is to place a light exuding cloth over the top of your Christmas cactus to ensure that it has a long enough period of darkness to promote flowering. (Read my article for more, if your flower buds are forming and then drop off, why is my Christmas cactus buds dropping?) 3. Prefers Being Pot Bound for Flowering Christmas cactus actually has a preference for smaller pots with their roots being somewhat restricted and pot bound. Christmas cactus does not necessary flower if they are not under some kind of stress. If the Christmas cactus is planted in a large pot then their energy tend to be redirected into growing out the roots system rather then into flowering. When the Cactus is pot bound it prioritizes producing flower buds over the growth and development of the plant as flowering is the plants way to reproduce as a strategy to survive even in hostile environments. If the plant is perfectly content with its conditions then there is less incentive to produce flowers as their is less of an urgent threat to its survival. Plant your Christmas cactus in a pot just larger then the root ball (rather then a large pot with excessive capacity) to help promote blooming. 4. Too Hot or Too Cold Can Prevent Christmas Cactus from Flowering The optimal growing temperature for Christmas cactus is around average room temperature of 68°F (20°C) but it can tolerate a wide range of temperatures due to its adaptability to fluctuating conditions in its mountainous rainforest environment. In the Northern hemisphere, Christmas cactus starts to develop its flower buds in September. The flower buds then develop for 6 weeks with a evening temperature slightly on the cooler side of approximately 60°F (15°C) but once the flowers have emerged they tend to last longer with a more consistent temperature of 68°F (20°C). This sequence of temperatures replicates the same cycle for bud formation in the Christmas cactus's native environment. Whilst these temperature range are best practice for promoting flower, I have personally seen an excellent display of flowers year after year when my plant is placed on a kitchen window sill which receives indirect bright light, slightly cooler temperatures and higher levels of humidity then other areas of the house without necessarily following a strict pattern of temperature change. However if your cactus is not flowering then keeping it nice and cool during bud formation is going to give it the best chance of flowering. 5. Overwatering Prevents Blooming Christmas cactus thrives and flowers best with an optimal balance of watering. Christmas cactus is an epiphytic plant (grows on trees) that attains water from the air or moist areas f the tree or plant where it grows. Therefore Christmas cactus has a preference for porous, aerated soil that holds some moisture yet allows water to drain quickly. If you water Christmas cactus too often or plant it in relatively compact soil, then this can exclude air from around the roots which can prevent effective root respiration and cause root rot which causing the cactus to droop or wilt and turn yellow. (There can be several reasons why Christmas cactus wilts other then overwatering read my my article why is my Christmas cactus wilting for the solutions). When the cactus is in overly damp soil it does not flower. Other causes of too much moisture around the roots are: Potting soil that has not been amended with sand grit or perlite. Ideally plant the cactus in soil that is 3 parts potting soil and 1 part grit to maintain porous soil structure. The use of saucers, trays and decorative outer pots. Empty any saucers trays or pots regularly that are used to prevent excess water spilling in your home. This prevents watering pooling around the roots which keeps the soil to damp and causes root rot. Empty decorative outer pots of water regularly. Water Christmas Cactus once a week with a generous soak and mist the leaves but allow the surface of the soil to dry to the touch to allow for an exchange of gas for root respiration. This helps to achieve the preferred balance of moisture for your cactus so that it can flower rather then suffer moisture stress or root rot. 6. Too Much Sun Impacts Flowering Whilst most cacti prefer full sun, Christmas cactus is a plant that has adapted to growing in bright, indirect light under a tree canopy. If the cactus is located in an area of sun the leaves turn purple or red as it tries to prevent sunburn. Full sun is contrary to the conditions to which it is adapted and the stress of too much sun prevent flowering and can cause drought due to drying out the pot too quickly and lower humidity. Place the cactus in an area of bright indirect light (rather then shade) to give the plant enough energy to flower but not to suffer sunburn or drought stress. 7. Too Much Fertilizer In Fall Prevents Flowering Christmas cactus are not necessarily heavy feeders and do not necessary require fertilizer for flowering. If you have been applying fertilizer during the period of bud formation from September then this is likely to prevent flowering and the plant can grow droopy. However a half strength liquid ordinary house plant fertilizer applied once per month during Spring and Summer can prevent any nutrient deficiency that can reduce flowering. Always apply at half strength and only feed once per month and avoid fertilizing from late Summer for optimal bud formation and more flowers. (Read my article, how to revive a dying Christmas cactus). Key Takeaways: Christmas cactus does not flower if it suffers from drought stress due to underwatering and low humidity and because of too many hours of light during flower bud formation. Christmas cactus requires frequent watering and regular misting and at least 12 hours of darkness for 6 weeks before flowering. The Christmas cactus prefers cooler temperatures of around 60°F (15°C) from September whilst the flower buds are forming to emulate the natural conditions in its native habit. Christmas cactus prefers temperatures around 68°F (20°C) for optimal growing conditions. Overwatering can cause the cactus stress and root rot which prevents flowering. Too much sun can burn the plant and dry it out quickly causing drought stress which can also prevent flowering.