Rose of Sharon leaves turn yellow when they do not have enough nitrogen for proper growth. Too much fertilizer can also cause yellowing or scorching, burning the roots and damaging the plant. Apply fertilizer only to moist soil, then water well to distribute the food evenly.
Not Enough Sunlight
Roses need at least six hours of sunlight per day in order to thrive. If your rose bush is not getting enough sunlight, you will notice that the leaves start to turn yellow due to stress. The best way to fix this problem is to transplant the rose bush to a sunnier location.
Your rose is overheating
As well as needing enough sunlight, roses can be sensitive to extremes of heat. This can dry out the leaves and cause them to turn yellow or brown. If your area experiences a heatwave, then take precautions by watering your rose every day.
Overwatered Hibiscus will develop yellow leaves and possibly experience leaf drop. If you are concerned that the Hibiscus has been overwatered, give the plant time to dry out and continue to check the soil's dampness before watering again.
An overabundance of sunlight can be the reason for yellow leaves on a hibiscus plant. Too much sun can cause the leaves to turn yellow and to develop white spots. If this occurs, remove the damaged leaves and move your hibiscus to an area with less sun exposure.
Overwatering flowers can be caused by too much water, fertilizer, or light. If you notice that your flowers are wilting, then you should check for these signs of overwatering. The flowers will be drooping and wilted. Leaves on the flowers may look yellowish.
When you see an entirely yellow leaf, you should remove it from your plant using a sterile cutting tool. Removing the leaf will let the plant focus its nutrients on healthy leaves. A yellow leaf has lost its chlorophyll (pigment) and it can't turn green again even after you correct the problem.
FOR ESTABLISHED ROSES:
Use a high-nitrogen fertilizer or top dress with alfalfa meal (5-1-2) for the first application to jump-start leaf development, along with epsom salts to encourage new cane development and lusher growth. Add a slow-release fertilizer when shoots are 4 to 5 inches long.
Nutritional problems
Yellowing of the areas between the veins (interveinal chlorosis) is usually indicative of manganese, iron or magnesium deficiency. Iron deficiency affects the youngest leaves first, whereas the symptoms of manganese and magnesium deficiency tend to start in the older leaves.
They are a fast-acting source for magnesium and sulfur. For soils on the alkaline side, the added sulfur is a benefit. Epsom salts, however, do not contain any of the three major components of most fertilizers—nitrogen, phosphorus or potassium—and therefore would not be a complete fertilizer for roses.
By adding coffee grounds to your roses, you create a barrier that will keep pests away and allow your rose bushes to thrive. So if you're wondering whether coffee grounds are good for roses, the answer is a resounding yes! Coffee grounds are an inexpensive and readily available organic fertilizer for your roses.
Nitrogen deficiency shows up as a general yellowing. Older, inner leaves turn yellow first. As it progresses, yellowing moves outward, eventually reaching young leaves, too. Potassium deficiency shows itself when leaf edges turn bright yellow, but the inner leaf stays green.
Over-fertilizing. People often use too much fertilizer to make their plants grow faster. The excess salt in the soil from too much fertilizer “burns” the leaves causing them to turn yellow. In the case of houseplants, change the soil or leach it with large amounts of water to correct the balance.
Yellowing leaves on plants may often be a sign of too little or too much water or nutrients which can affect plant performance. Your plant may also be located in too much light where it is scorching, or too little light where it is fading due to an inability to photosynthesize properly.
Yellowing leaves: Usually accompanied by new growth falling, yellow leaves are an indication of overwatering. However, yellow, curling lower leaves can also be an indication of underwatering. Check the soil for moisture to decide which it may be.
Yellow Leaves + Fading to Green + or Bright Yellow =
These symptoms together mean that your plant is overwatered. Usually lower leaves drop first, although the whole plant may be affected. The solution = repot (to remove soaked soil) and water less, or let soil dry out and water less.
Overwatering
Watering issues are generally the most common cause of yellowing leaves. When your plants are overwatered, the performance and vigor decrease. Oxygen is being pushed out of the soil, and the roots are simply “under aired” and suffocating. With little air, the roots will begin to drown and rot.
Epsom salts work well for hibiscus planted in the ground in areas with neutral or acidic soil, or for plant in pots where the water drains out the bottom and isn't constantly taken back up into the pot.
Vinegar Solutions
Dilute a cup of vinegar in a gallon of water and pour the whole solution onto the roots of the plant. The solution, which settles around the roots, unlocks vital nutrients in the soil, feeding hibiscus plants.
When temperatures are extremely hot, especially in summer, the hibiscus requires additional watering. Otherwise, the plant will dry up quickly and succumb to heat stress. This can result in the hibiscus leaf turning yellow and eventually dropping off.