Bulbs in the ground that have bloomed well in the past may not need added fertilizer. The more important factor is good drainage and for some bulbs like agapanthus, lots of sunshine. You can use a slow release plant food like Osmocote scattered on top of the soil and then mixed into the top inch of the soil but wait until mid spring like April or early May when the soil has warmed a bit. Most bulbs make next year's blooms after they flower so fertilizing once the flowers have faded is another good tip to ensure better blooms in the following year. Be sure not to disturb the foliage on bulbs after they flower. As the leaves turn yellow they send energy down to the bulb that is forming the flowers for the following year. Sounds like you will have a beautiful garden this spring and summer. Keep growing, Marianne Binetti