There are two big reasons people buy a Christmas cactus plant: how it looks and its holiday bloom.
Here’s the catch. The Thanksgiving cactus is the one most often found for sale during the winter holidays, so the plant you brought home may be one of its close relatives.
The three holiday cacti share similar care requirements. Bloom time and stem shape are where they differ.
Fertilizing is where the timing gets confusing, so here’s what university extension guidance says about what to feed, when to feed and when to stop.
Which Holiday Cactus Do You Have?
Christmas, Thanksgiving and Easter cactus look alike, and they’re easy to mix up. The feeding advice below is extension guidance for holiday cacti as a group, so it works whichever one you have.
Best Fertilizer for Christmas Cactus
Holiday cacti are epiphytes. They grow among tree branches in shady rain forests, and these epiphytic cacti do not grow well in heavy, wet potting mixes.
For feeding, Clemson Extension recommends a half-strength soluble fertilizer, such as a 20-10-20 or 20-20-20 with trace elements. The three numbers are the percentages by weight of nitrogen (N), phosphorus (P) and potassium (K).
Another simple option is a balanced houseplant fertilizer at half strength. In the fall, when flower buds are forming, you can change to a formula that is low in nitrogen and high in phosphorus and potassium, with 0-15-10 as an example.
Liquid or slow-release? Water-soluble fertilizers are often preferred because dilute solutions reduce the potential for fertilizer burn. UF/IFAS Extension says soluble fertilizers and slow-release products are both acceptable, and a balanced, slow-release fertilizer during the growing season is also recommended. Either way, reduce the label rate, because excess fertilizer salts can damage the roots.
Products vary a lot, so the label on yours sets its rate. For example, Espoma’s Indoor! Plant Food is a natural and organic liquid concentrate mixed at 1/2 cap (2 teaspoons) per quart, and its page says an 8-ounce bottle makes up to 24 quarts. Miracle-Gro Indoor Plant Food lists a 1-1-1 analysis, and its page says to apply once a week. Those directions differ from the half-strength monthly routine extension gives for a 20-10-20 or 20-20-20, so read the label before you decide how much and how often.
When or How to Fertilize Christmas Cactus
Feed about once a month, starting when new growth begins in late winter or early spring and continuing through the summer. Schedules vary: some put the growing season at April to September with feeding every one to two months, and others say monthly from June through August at half strength.
Then stop in late summer. Stopping fertilizer during the late summer gives greater flower bud production in the fall. Other advice is a little looser: reduce or cease fertilizing in fall and winter, when the plant is dormant, and Missouri Botanical Garden also says to reduce fertilization during fall and winter. Another version is to switch to that low-nitrogen, high-phosphorus and potassium formula in the fall while buds form.
One more fall note: after the buds set, keep the potting mix evenly moist to prevent bud drop.
To apply, mix the fertilizer at half strength, pour it slowly onto the potting mix so nothing splashes, and work your way around the pot, lifting the stems where you need to.
Epsom Salts: An Optional Magnesium Boost
Holiday cacti have a higher requirement for magnesium than many plants. Epsom salts (magnesium sulfate) can be given monthly during the growing season, mixed at 1 teaspoon per gallon of water, but not in the same week as the regular fertilizer.
Mind the amount: 1 teaspoon per gallon, not a tablespoon. Garden guidance on Epsom salt says magnesium is generally already sufficient in most garden spaces and that too much adds unnecessary salt, and University of Minnesota Extension says to use Epsom salts only if a soil test shows a magnesium deficiency. Those two pages are about garden soil, not potted holiday cacti, so treat Epsom salts as an optional extra rather than a must-have.
Final Tips
Fertilizer is salt-based, and salts can build up. Colorado State University Extension says many fertilizers are salt based and that salts are left behind as moisture evaporates from the soil. Its signs of buildup are brown leaf tips, yellowing leaves, unaccountable wilting and a whitish crust around the lip of the pot or on top of the soil.
To prevent it, water thoroughly so water drains from the bottom of the pot, discard what drains out and don’t let the plant stand in it. If buildup has already started, scrape off the crust and remove half an inch to an inch of potting mix from the surface. Then rinse the mix by filling the pot to the top with tepid water a couple of times, letting it drain well between rinses, and replace what you removed with new mix. In extreme cases the soil may need to be changed and the plant repotted.
For everyday watering, water only when the upper inch of the potting mix feels dry, and avoid letting the plants get too dry between waterings.
Holiday cacti flower best when kept somewhat pot bound, and repotting is necessary only about once every three years, best done in spring. The plant prefers to be a bit root-bound, so don’t choose a pot that’s too large. A good example mix is 60 to 80% potting soil with 40 to 20% perlite.
Get the timing right and the plant does the rest. Holiday cacti can live over 100 years and are often passed down from generation to generation, so a little care now can pay off for a very long time.
Frequently Asked Questions
What is the best fertilizer for Christmas cactus?
Use a half-strength soluble fertilizer, such as a 20-10-20 or 20-20-20 with trace elements, fed about monthly from early spring through summer. A balanced houseplant fertilizer at half strength also works. Your product’s label sets its own directions, so read it before you mix.
What is the best liquid fertilizer for Christmas cactus?
Water-soluble fertilizers are often preferred because dilute solutions reduce the potential for fertilizer burn, and for holiday cacti a half-strength soluble product such as a 20-10-20 or 20-20-20 is a good choice. Slow-release products are acceptable too; reduce the label rate because excess fertilizer salts can damage the roots.
When should I stop fertilizing a Christmas cactus?
Stop in late summer. That gives greater flower bud production in the fall. Looser advice is to reduce or cease fertilizing in fall and winter instead, or to switch to a low-nitrogen, high-phosphorus and potassium formula once buds form. Start monthly feeding again when new growth begins in late winter or early spring.
Can I use Epsom salts on a Christmas cactus?
Holiday cactus guidance suggests 1 teaspoon per gallon of water monthly during the growing season, in a different week than the regular fertilizer, because these cacti need more magnesium than many plants. Separate garden guidance says magnesium is generally already sufficient in most garden spaces, that too much Epsom salt adds unnecessary salt, and to use it only if a soil test shows a magnesium deficiency. Those pages are about garden soil.
How do I fix fertilizer salt buildup in a Christmas cactus pot?
The telltale sign is a whitish crust on the pot’s rim or the soil surface. Scrape off the crust and up to an inch of potting mix, rinse what’s left by filling the pot with tepid water a couple of times and letting it drain between rinses, then replace the mix you removed with fresh. Watering thoroughly and discarding the drainage helps prevent it.