House Plants/soil PH
I have a large curly leaf Hoya that my mother had, I inherited it 7 years ago. The first year it lost many leaves so thinking it may need repotting I got a little larger pot, and made a new trellis for it as it had 5 long branches, each about 4' long. When Mom had it, about twice a year it would bloom a few small flowers. It has since regrown all of it's leaves and them some and also grew another branch that is now about 3' long but in 7 years it has not bloomed. I water it regularly and use a fertilizer for house plants like she did but it has not bloomed for me, I checked the PH of the soil a couple days ago and it is about 5.5, any suggestions?
Hoyas can stand soil ph from 5 to 6.5. To increase it use lime. If you are talking about just the one plant you might dissolve 1 tablespoon of baking soda in a quart of water and water it with that for a couple of waterings then wait a week and check it again.
To get it to bloom do not repot it into a larger pot, keep it somewhat potbound, that will encourage blooms. Be sure to use a fertilizer that says it is for blooming plants and sprinkle 2 teaspoons of Epsom salts on top of the soil then water. Epsom salts is magnesium sulfate and will trigger many blooming plants to bloom. Low humidity and not enough sun are another reason hoyas do not bloom.
Long stringy growth are bloom spurs and should not be be cut back. Peduncles (bloom spurs) should not be pruned unless desired. A few hoya species shed these bloom spurs after blooming and form new ones each year. Do not spray hoyas with anything but water if temperatures are over 80° F (26° C).
Above is a great sight that has more info on hoyas. Good luck!