Most spring-blooming bulbs are now finished flowering. To ensure you will have a nice bulb show next spring, resist any temptation to cut back the foliage of bulb plants such as tulips and daffodils to tidy up the garden.
“The plants need those leaves for at least several more weeks,” said Spencer Campbell, Plant Clinic manager at The Morton Arboretum in Lisle. “This is the critical time when they are creating and storing their flowers for next year, and they need leaves to do it.”
All bulb plants — including hyacinths, crocuses and glory-of-the-snow, as well as daffodils and tulips — form a new plant and flower in the weeks after they bloom and stash it with a food supply to store through the winter dormant season until spring. “That’s what a bulb is,” Campbell said. “It’s a handy package of plant, flower and food.”
Creating that package is energy-intensive, and leaves are the solar collectors that supply a plant with its energy. “Leave bulb leaves until they begin to turn yellow,” he said. “Yellowing is an indication that the job is done and the plant doesn’t need the leaves anymore.” For some species and cultivars, the leaves may not turn yellow until July.
“You don’t need to cut back the leaves at all if you’re not concerned about their appearance,” he said. “They’ll eventually dry up on their own.” Most of the tens of thousands of daffodils at the Arboretum are left alone.
Here are some more tips for success with bulbs.
Remove spent flowers. Although you should let the leaves stand, unsightly dried-up blooms can go. Cut off the whole flower stalk close to the ground.
If you fertilize, do it now. Bulbs growing in good soil with plenty of organic matter likely don’t need fertilizing, but if you want to give them a little nutrient boost, scatter slow-release fertilizer around the plants after they flower. Because a bulb already contains food, there’s no need to fertilize at planting or before the plants bloom. The most hard-working part of these plants’ life cycle, when they are most likely to need extra nutrients, is in the few weeks after they finish blooming.
Make some notes. Before the plants dry up and you forget all about them, make some notes about this year’s flower display. Are there places where you’d like to add more spring color? Was there some flower you really loved and you’d like more of? “These notes will be useful in August or September when it’s time to buy bulbs for fall planting,” Campbell said.
Transplant or divide bulb plants. If you have bulbs growing in the wrong place, move them while their leaves are still green and easy to spot. This is also the time to divide clumps of daffodils that are blooming less because they have become crowded.
Consider companion plants to conceal bulb leaves. The foliage of bulb plants will be less conspicuous after flowering if they are growing among perennials that take over attention. “Daffodils planted among daylilies become almost invisible because they have such similar leaves,” he said. “Hostas are a classic companion plant for the more shade-tolerant bulbs such as snowdrops.”
Let the little ones live in the lawn. Low-flowering bulbs such as Siberian squill often spread into grass, where squill can form a blue carpet in early spring. Some gardeners deliberately plant small bulbs such as crocus, Siberian squill, striped squill (Puschkinia) and glory-of-the-snow in their lawns. “Just leave them alone after they bloom,” Campbell said. Their long, slender leaves are so similar to blades of grass that they will be inconspicuous.
If possible, delay mowing until late April or early May, so the bulb plants keep their whole leaves a little longer. Set your lawnmower’s blade at the highest level to cut your grass at 3 inches or taller. “Those practices are good for your grass, and they’ll also give your sparkly little spring bulbs a little help,” he said.
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.