Unless you remove the ivy completely it will simply grow back and swamp the plants. The soil is also likely to be dry as well as impoverished and the feed is going to make the ivy very happy.

This is an ongoing problem in my garden too, ivy clad walls. Even though ivy is a great wild life friendly plant,it does take some keeping in check and can rid the soil of nutrients. Also ivy seedlings are a constant battle too. The first foot of soil from my wall is usually bone dry and any climbers would have to be planted at an angle towards the wall, so the roots are in moist and fertile soil.

The plants that I've found cope okay at the foot of my south facing wall are the Nepetas, evergreen Iris foetidissima, Monkshood and Honeysuckle. Yes I think you'll find adding compost will be an ongoing necessity and watering well in the height of summer, as the heat from the wall will dry the soil even more.

Hi,
Lets try to tell you why your doing all this wrong,
Ivy is a plant in its self, and its a plant you dont want anymore,

this ivy has more than likely been living in the ground "In very poor soil conditions " And growing.

You've come along and improved its compost, fed it by supplying it with one of the best long term feeds you could ie bone, and blood/fish is an added bonus for the ivy,
The ivy thinks its christmas.

Because ivy is a strong grower in poor soil, it will really speed up now you've given it all this food.

So you must get rid of the ivy first,
Do this by removing the newly planted (3 plants) you've put there and pot them up or plant them in a clear of ivy plot.

Now to clear this spot of ivy you'll need to do as you've said you did ie clear all roots, check by really digging deep to ensure you've really done a first class job,
refill the area with the soil and I'd wait to see if any ivy re-appears!
If it should re-appear then much to my dislike of chemicle use you can use the touch chemicle that will soak into the stems of your ivy and kill the roots,

The reason ive said remove your (3) plants is so you can really have time to see if the ivy re-appears and give yourself time to deal with it & without the ivy getting to near to your (3) plants and making it very difficult to apply any chemicle to just the ivy.

Its a task that will take a little time "but if done correctly" it's a job worth doing.

I would definitely put all your new plants in pots or containers and wait to see what happens.

Thank you all for your suggestions. I will let you know how things go.