I have planted petunias over tulip bulbs. Is that o.k., and also, how and when can I fertilize tulips this fall?
Your idea of planting a later blooming plant over the tulips is just fine. It will conceal the dying foliage nicely. According to The Plant Care Manual by Stefan Buczacki (Crown,1993), the time to fertilize tulips–if you need to fertilize them at all–is early spring. They can be mulched (with compost, for example) in early fall and spring, and given liquid feed 2-3 times after blooming and while still in full leaf.
The Brooklyn Botanic Garden’s Spring-Blooming Bulbs (2002) gives the following general advice:
“Most bulbs do better with regular fertilizing, and bulb fertilizer is one good choice. Some gardeners prefer to use bone meal (though the way it is processed today saps most of its nutrients) or rock phosphate. Even better is a healthy dose of compost–in fact, if you regularly improve the overall quality of your soil with compost and other organic amendments, you don’t have to provide much fertilizer for most bulbs. Mix compost or fertilizer into the soil when you’re planting or top-dress, following label directions. to help boost the bulbs for next year’s bloom, you can also top-dress the soil in spring after blooming. Remember to work any fertilizers well into the soil, and avoid high-nitrogen fertilizers (like lawn fertilizer).”
You may not need to fertilize your tulips if they are the showy varieties (the ones that don’t come back year after year in the garden). Seattle-area gardening expert Ciscoe Morris says the following:
“Don’t fertilize spring-blooming bulbs if you’re going to replace them next fall. Most books recommend adding bone meal and fertilizer whenever you plant spring-blooming bulbs. That’s only necessary if the bulbs you’re planting are the kind that tend to naturalize and return to bloom every spring for years to come. Those bulbs not only need fertilizing at planting time, but also should be fed every spring thereafter. On the other hand, most of the big, showy tulips are ill-suited for our rainy cold winters and rarely perform well the second year. If, like most of us, you treat them as annuals and replace the bulbs every year, don’t waste time and money fertilizing them. These bulbs already contain everything they need to grow and bloom, and as long as the bulbs don’t rot as the result of poor drainage, and nothing eats them, they’ll put on a great display without the addition of nutrients.”