Your article about Clivias was very good. You mentioned 20-20-20 fertilizer, which I have never heard of. Can you explain what this is? Is there a commercial fertilizer that I can buy?
Yes, there are many different 20-20-20 fertilizers available at gardening stores, hardware stores, and online. The three numbers refer to the amounts of nitrogen, phosphorus, and potassium the fertilizer provides:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/fertilizer-numbers-npk.htm
My clivia plant is kept in the conservatory in summer and indoors in winter; however, the leaves are turning yellow. What is the problem and what can I do about it?
Yellowing leaves are generally an indicator of watering issues. To much or to little.
Make sure the soil dries slightly between waterings. Check the soil, don't water on a schedule.
Also insects or disease can cause yellowing leaves. Check for signs of insects and treat with Neem Oil if indicated.
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
Have a clivia houseplant. Am interested in how to care for this plant and what problems it may be susceptible to. When to repot, how to divide or pot side plants that are growing? Any info would be appreciated.
See these articles for general information and how to divide clivia:
https://www.gardeningknowhow.com/ornamental/flowers/clivia/clivia-plant.htm
https://www.rhs.org.uk/advice/profile?PID=655
Clivia should be kept in the same pot for at least three years to avoid disturbing the roots too often. After that, it can be repotted when the plant is too large for its pot. See this article for how to tell:
https://extension.psu.edu/plants/gardening/fact-sheets/houseplants/repotting-houseplants
My clivia bloom stayed inside the leaves. It did not grow a stalk. Why? Thank you!
This actually can be common, especially the first time that your Clivia blooms.
A cooler location can help along with feeding with a soluble fertilizer is the most effective way to induce the peduncle to grow normally.
https://www.gardeningknowhow.com/ornamental/flowers/clivia/clivia-plant.htm
After my Clivia plant bloomed, there appeared what looked like small red berries. It has been like that for a year. I have finally cut the stem off - have I ruined anything?
When the seeds turned to yellow or red, they were mature and can be removed from the plant. These matured seeds can be germinated into new plants.
You can remove the seeds and just toss. You did not harm your plant in any way.
https://www.gardeningknowhow.com/ornamental/flowers/clivia/clivia-plant.htm
what would cause the flower to snap off the clivia plant???
Slugs and Snails can dine on Clivia plants.
Thrips can also attack the plant and cut off the flowers.
https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm
https://www.gardeningknowhow.com/plant-problems/pests/insects/kill-garden-slugs.htm
https://www.gardeningknowhow.com/ornamental/flowers/clivia/clivia-plant.htm
Should I cut off the stalk after my clivia has dropped it's flowers?
Go ahead and cut off the flower stem. Unless you are trying to raise and collect clivia seeds it is best to remove old flower stems so the plant can put energy into producing more flowers instead of maturing seeds. A plant's primary objective is continuation of the species. By removing flower stems before seed develops the plant is encouraged to bloom again.