I use 8-8-8 on my young Satsuma - mid February and again in May.
Even with the huge, old, live oak removed the lawn in the back is still nitrogen poor. Clover is a sure sigh of a nitrogen deficiency. I apply granulated Ammonium Nitrate at the rate of 1 Lb. per 100 Sq. Ft. - water in. Before the tree was removed I did this 3 times a year. With the tree gone I will have to have the soil tested annually for 2 or 3 years. My first application will be this coming week. This week has been the last of our winter weather.
The vegetable boxes and herb bed usually do fine with seasonal additions of compost. I do have the soil tested every year or 2. I occasionally need to add nitrogen.
The potted plants are planted in a 50/50 mixture of all purpose potting soil and compost. The Plumeria plants do get fed. They over winter in the shop. No care at all over winter. After the last frost - hopefully this coming week - I will take them out and begin with heavy watering - 3 times a week for a couple of weeks. I also use a water soluble fertilizer with a high P. They are heavy feeders so I give them a shot of fertilizer at 4 to 6 week intervals. I also give them Epsom salt - 1 tbsp. to a gallon of water - every month or 2.
I have a Sweet Olive in a very large clay pot. I have not re-potted it in several years so I do feed it with water soluble fertilizer a couple of times a year and dose periodically with Epsom Salt. It does need the soil refreshed but the huge pot is difficult to handle. I was hoping to get G to help me this spring but he has been having trouble with his shoulder. I don't know if he will be able to handle the weight of the pot.
Sorry for getting off of the subject.
Osmacote is good for your pots. Use the right balance of NPK. Higher N if they are foliage plants and higher P if they bloom. I like a periodic addition of Epsom Salt for blooming plants.
I do not like spikes. As a landscape contractor and having worked in a Lowe's garden center I have seen too many plants damaged by spikes. Don't like them, will not use them and do not recommend them.
When dealing with garden beds, lawns and landscaping/flower beds I HIGHLY recommend regular soil test. Well worth the money. Random fertilization is the equivalent of a Doctor writing a prescription without a diagnosis. You need to know your starting point before amending your soil. You will spend more on unneeded amendments than the cost of soil test.
When it comes to fertilizer more is not better.
With potted plants soil test would be too costly. If your foliage plants have good foliage color and if your blooming plants produce blooms then don't worry too much about fertilizer. With the exception of heavy feeders limit your fertilization to 2 or 3 times per year - depending on the length of your growing season. Over fertilizing potted plants will result in a high level of sodium. Not good for your plants.