Have you been fertilizing them? They could just be hungry. Hibiscus need more food than most.

They look like the oldest leaves turning yellow. Your plants are still getting established. Hibiscus can tolerate indoor conditions, but really thrive once outdoors in summer where there will be more light, more warmth and more humidity. Once you place them outside for the summer, they'll grow gangbusters. I wouldn't be overly concerned. Just make sure you don't let them go too dry.

I agree that, if you haven't been fertilizing you should be, because availability of all essential nutrients is essential to normal growth. Nutritional deficiencies of any of the mobile nutrients (nitrogen, phosphorous, potassium, magnesium), but especially nitrogen, force the plant to cannibalize it's older foliage, robbing the nutrients from old leaves to provide the building blocks plants need to grow, something that certainly warrants concern. This results in the shedding of the old leaves which is conspicuous in your images. To be fair, there are other things that 'could' be causal, but if you haven't been fertilizing, it makes the most sense to start there.

Hibiscus is a strange plant when it comes to it's nutritional wants. It is one of the few plants that uses more potassium (K) than nitrogen and isn't all that crazy about phosphorous, either. A fertilizer something like a 2:1:3 ratio would serve you well. They aren't that easy to find, so I have developed a strategy (for my own plants) they like. I use Foliage-Pro 9-3-6, and alternate with ProteKt 0-0-3. This raises the amt of potassium delivered (which they need) and keeps phosphorous about where it should be relative to N. I've had very good results using that strategy.

Al

A company called BGI makes a special food for them called Hibisgain.

@iochroma @doriswk Tropical hibiscus are widely known as being unusual in their nutritional wants in that they use/want more potassium (K) than nitrogen (N) and want very low rates of phosphorous (P) compared to N. The average plant needs about 16% as much P as N, hibiscus even less. High P fertilizers are inappropriate for use on containerized hibiscus for that reason. A 12-6-8 fertilizer provides about 22% as much P as N (high for hibiscus), but more importantly supplies only 55% as much K as N, which is very low for hibiscus, which are heavy users of K. If you do a quick search for "hibiscus fertilizer", you'll soon realize that many products are nothing more than a random fertilizer product with a label indicating 'for hibiscus', some even adding 'and tropical plants' to hook more potential customers; whereas, fertilizer products actually formulated for tropical hibiscus in containers usually have lower P levels than usual (middle number representing P content less than 1/3 of N, and the number representing K content being notably larger than N, making the level of K primarily what makes hibiscus an outlier when it comes to their nutritional wants. Based on the products BGI supplies, I would suggest their Palm Fertilizer as being the most appropriate product they sell for the nutritional needs of hibiscus, going as far as to say it should actually be a great choice.

Nutritional needs of containerized hibiscus.

Al

They probably lack fertilizer, I normally don't fertilize my plants during winter, but I see now that these are still babies and were probably starving...thank you all for the good suggestions, will follow through!

Thank you Al for all the info. I did purchase Foliage-Pro 9-3-6 and also ProteKt 0-0-3. They are big containers and should last a long time. Coming back to what you suggested earlier for hibiscus: An ideal fertilizer should have a 2:1:3 ratio, and you achieve this by using Foliage-Pro 9-3-6, and alternate with ProteKt 0-0-3.

Firstly, why alternate and not combine these two fertilizers in one feeding ? ( I'd likely forget which they already received and which not...)

Secondly, the combined ratio would then be a 3:1:3 ratio. ...a matter of "as good as it gets"?

Thirdly, what other houseplants do you use Foliage-Pro 9-3-6 for?

I use it on ALL containerized plants, indoor or outdoor.

Good (9-3-6). It can be your go to fertilizer for anything else you're likely to grow other than tomatoes and hibiscus.

If you mix ProTeKt 0-0-3 with acid-forming fertilizer products (like FP 9-3-6), the ProTeKt can combine with other ingredients and precipitate out of the solution. To help avoid this, fill your watering can with water, add the ProTeKt, mix, then add the fertilizer.

You can add a larger measure of the ProTeKt 0-0-3 than the FP 9-3-6 to raise the level of potassium to something closer to 3-1-5 for hibiscus; or, you could add a little POTASH to your fertilizer solution whenever you fertigate. The silica in the ProTeKt is reason enough on its own to utilize ProTeKt as a source of additional potassium.

I use it on everything I grow in containers. There is plenty of evidence from reliable sources that 3:1:2 ratio fertilizers are most appropriate for almost all containerized plants. FL State University publishes production guides for most plants commonly grown as houseplants, and 3:1:2 ratio fertilizers are almost invariably recommended. The attributes inherent in Foliage-Pro 9-3-6 sets it apart of one of the best of the best, if not THE best fertilizer choice for houseplants and other plants in containers. The only reason the recommendation cannot be broadened to include plants in the landscape is because when selecting fertilizer products for plants grown out, the current levels of nutrient availability (what's already in the soil) must be considered an essential part of determining what products are necessary/appropriate.

Al

My hibiscus are looking healthier already after I ve been applying Foliage-Pro 9-3-6 ! In the next watering they will get the ProTeKt 0-0-3. I know they will do so much better once I can place them outdoors, but they may have to wait until mid May.

As for the Foliage-Pro 9-3-6, can I also use it on my new vegetable and flower seedlings while they are still indoors in small cell packs and pots ? Such as tomato, peppers, basil, pansies etc. ? Once planted in the outdoor garden, I typically give them an organic 4-6-8 Tomato fertilizer, but want to give them a good start indoors... last year I gave them a liquid seaweed fertilizer but they started to look pale / yellow in the last few weeks....

Yes, FP 9-3-6 is a complete nutritional supplementation product and an appropriate fertilizer for seedlings that have at least the first true leaves.

Al

Al, one more question about feeding hibiscus Foliage-Pro 9-3-6 and ProTeKt 0-0-3. Can I pour these two liquids together once I have prepared them, and then fertilize the plants once with both products simultaneously, instead of alternating as you suggested ? By alternating I can't keep track of which planters received what, as the small seedlings in small pots require more feeding at different times than the big shrubs in big pots...

I addressed that above because it is an issue.

"If you mix ProTeKt 0-0-3 with acid-forming fertilizer products (like FP 9-3-6), the ProTeKt can combine with other ingredients and precipitate out of the solution. To help avoid this, fill your watering can with water, add the ProTeKt, mix, then add the fertilizer."

Al

I think I was not clear. I have filled one jar with water and ProTect, and another gallon jar with Foliage pro 9-3-6 because I use Foliage pro 9-3-6 for other plants as well. This way both products are already pre-mixed in water and ready to use... Can I then mix the two diluted blends together in a watering can for just watering the hibiscus ?

Yes, but if you see a white precipitant at the bottom of the container ......

If you get a precipitate and need help keep track of what plant needs what, apply either fertilizer or 9-3-6 when you add the second item to the pot, then use the other solution when you're about to add the 4th item (or 5th or however it works out), then repeat the cycle. Easy peasy - no counting, keeping track, or unnecessary fuss.

Al