Care of Summer-Blooming Bulbs
Bulbs are pretty easygoing, but with these tips you can help maximize blooms and increase the odds that they'll naturalize into more plants
If you've planted bulbs in the fall, you know how easy it is, and the process is similar with summer-blooming varieties that thrive in peak heat. To get the most out of these plants, we checked in with bulb guru Brent Heath, part of the team behind 's, the bulb catalog. Here, Heath offers advice on planting and feeding the bulbs once the ground thaws in spring, and tells how to encourage them to make new plants.
Typically, most bulbs should be planted in holes that are three times as deep as the bulbs are tall. True tubers, like dahlias and liatris, should be buried only as deep as the crown. "Bulbs do best in free-draining soils, though summer-blooming bulbs are a bit more tolerant of wet feet, compared with ones that bloom in the fall, because the cooler spring dormant period is hospitable to fungi," Heath says. Sandy soil is better than heavy clay, but you can amend dense soil. Heath recommends adding a layer of compost above the clay, instead of mixing the two, which creates something of a bog. Layering the compost allows the bulb's roots to drain and reach into the clay, which is great for holding nutrients and moisture.
"A lot of the advice out there advocates adding a pinch of fertilizer to the hole when planting, but it's not necessary and it can burn emerging roots," Heath says. The bulbs already have the blooms within, so they're prepped for the first year's show. How well a plant blooms in subsequent years depends on the quality of the soil, which Heath says should have a high amount of organic matter instead of relying on chemicals fertilizers. Those give that initial boost but leave the plant in a slump afterward. "It's better to have a more sustainable nutrient base provided by compost," Heath says. "But if you have to fertilize after Year One, use a slow-release, organic version like Espoma Bulb-tone." Think of fertilizing as boosting next year's growth, because it takes some time to reach the plant's root zone. Compost tea applied as a spray stimulates the life of the soil, reaches the roots faster, and can be applied at nearly any time of the year.
Leaving the spent foliage on the bulbs allows them to recharge, developing starches and sugars for next year's blooms. But it doesn't always look so great, so it's smart to plant the bulbs among other, taller perennials that will bloom when the summer-flowering bulbs fade, helping to block some of that foliage. "Plant summer bloomers with asters and mums that will tide your beds over into autumn," Heath says. Wait until the foliage starts to turn yellow and flop over in fall; that's when it's done feeding for the season and can be trimmed down to the ground.
Shown: Asiatic Hybrid Lilies (Lilium Malta) and Shasta Daisies (Chrysanthemum maximum Little Princess)
There is a difference between perennializing and naturalizing bulbs. Many bulbs perennialize, or come back for two or three years and maybe increase in size. When a bulb naturalizes it spreads and makes additional separate plants, a process that can take three to five years and relies on the seed landing in a fertile spot where it won't have too much competition from other plants. To give plants a better chance of naturalizing, space them out in a border, where there's less competition for soil, nutrients, and light. Adding a trowelful of compost on top of the bulbs when planting is also a good idea. After the first year, broadcast a balanced fertilizer over the bulbs, and top-dress with more compost.
The most important part of dividing a bulb is the timing. "Divide when the plant is finished growing for the season," Heath says. "So that's May or June for the spring-flowering bulbs, the end of the summer for summer-flowering bulbs." Typically, bulbs ready to be divided will naturally fall off from the mother plant when you dig the clump up, and they can be replanted again right away. It's different from dividing a hosta, which you physically have to cut. With bulbs, gently tease them apart, and if they're not visibly attached they'll fall off. You may want to hold summer-flowing bulbs over the winter in a pile of peat moss or some wood shavings, because it's easier to establish them in the spring than it is in the fall. Heath says a common mistake is washing the bulbs you plan to overwinter, because you can bruise them, leading to rot.