Little bulbs, big problem when they go wild

A smart move in fall: Avoiding weedy bulbs

A friend who attends your webinars (I can’t! I work on Saturdays!) told me about how awful star of Bethlehem bulbs can be and that people plant them without knowing they take over, spread and can kill other plants. How terrible! That’s nightmare stuff. I like bulbs in my garden but until now I’ve stuck with daffodils and tulips. I do peruse the catalogs and sometimes think about buying others. Can you give me a list of which ones I should NOT plant, if there are others like this star of Bethlehem? -B.T. -

Star of Bethlehem or nap-at-noon (Ornithogalum umbellatum) really is a nightmare plant. There are others that spread uncontrollably but no other bulbs that we know that are allelopaths, too – meaning they stunt or kill other species via chemicals they produce and release to the soil. (How-to details for eradicating such bulbs are in the transcript of the Bulbs webinar Q&A. That transcript’s in the works. Watch for it to be posted here: https://gardenatoz.org/about-us/webinars-appearances-calendar/webinar-audience-notes/#Bulbs

 

We warn people who want only stay-put bulbs to avoid those below. Most are bulbs of small stature that are very early to grow, bloom and go dormant for the year. For instance, woodland anemone (Anemone blanda) is up, bloomed, and gone before mid-May and is so low to the ground that there is never a need to cut back its inch-high foliage. What bugs people about these bulbs is that they spread by seed into bare spaces between other perennials and where lawngrass is thin. For a few weeks in spring as their foliage yellows into dormancy their presence can change the color of a lawn or very low growing groundcover.

 

Woodland anemone (A. blanda) is a cheerful little plant that’s up, bloomed and gone dormant by mid-May. Its footprint is so light that many people (us!) tolerate its spread into bare spaces all over the yard.

Woodland anemone (A. blanda) is a cheerful little plant that’s up, bloomed and gone dormant by mid-May. Its footprint is so light that many people (us!) tolerate its spread into bare spaces all over the yard.

No condemnation just warnings

We don’t condemn these bulbs, simply warn you what to expect. We plant them, expecting and accepting their waywardness, and mulch over them in spring wherever later-emerging perennials have not already covered the bulbs’ remains.

Self-sowing bulbs, not suited to a precisely planned garden

Group 1 of 3: Offenders many people accept. Small, early species.

Grape hyacinth (Muscari armeniacum). Sterile variety ‘Saffier’ and cousin species M. latifolium are better bets where you want low, early blue without spread.

Snowdrops (Galanthus nivalis)

Squill (Scilla sibirica)

Striped squill or puschkinia (Puschkinia scillioides, literally, the squill-like Puschkinia).

Winter aconite (Eranthis hyemalis)

Woodland anemone (Anemone blanda)

Grape hyacinth’s blue can’t be beat but it also can’t be stopped spreading. We gain a fighting chance by planting slower-growing species and sterile varieties (no seed). Its foliage season begins in fall and that first wave is often damaged by winter cold. Those discolored leaves might look a bit shabby amid the newer foliage and blooms in spring.

Grape hyacinth’s blue can’t be beat but it also can’t be stopped spreading. We gain a fighting chance by planting slower-growing species and sterile varieties (no seed). Its foliage season begins in fall and that first wave is often damaged by winter cold. Those discolored leaves might look a bit shabby amid the newer foliage and blooms in spring.

Snowdrops (Galanthus nivalis) are often the first blooms of the year in a zone 5-6 garden. The plants have disappeared into dormancy by May but they set a lot of viable seed by then, too.

Snowdrops (Galanthus nivalis) are often the first blooms of the year in a zone 5-6 garden. The plants have disappeared into dormancy by May but they set a lot of viable seed by then, too.

Its flowers are a blue worth having but you then must accept the plant’s super-spreader character. Seeds of squill (Scilla siberica) will grow in the smallest opening between perennials and in thin lawn. A lawn full of squill is charming in bloom but many people cannot abide the two- or three week period of yellow cast the fading bulb foliage brings to the lawn.

Squill (Scilla siberica)

Squill (Scilla siberica)

Come on, admit it, you’d fall for striped squill (Puschkinia scillioides), too.

Come on, admit it, you’d fall for striped squill (Puschkinia scillioides), too.

Puschkinia doesn’t spread with quite the vigor of Siberian squill but if you plant it you should expect it to form large colonies.

Puschkinia doesn’t spread with quite the vigor of Siberian squill but if you plant it you should expect it to form large colonies.

We love to plant winter aconite (Eranthis hyemalis) and let them spread golden cheer through a shaded area in early spring. It usually starts quite slowly but in time, seedlings begin to appear and the colony spreads.

We love to plant winter aconite (Eranthis hyemalis) and let them spread golden cheer through a shaded area in early spring. It usually starts quite slowly but in time, seedlings begin to appear and the colony spreads.

Group 2 of 3: Worse and worst offenders

Bluebells (Hyacinthoides species). Called bluebells (English-, Spanish-, woodland-) they are larger and later than the lesser offenders and multiply forcefully. That is, growing clumps of bluebell bulbs can actually squeeze out other plants.

Star of Bethlehem (Ornithogalum umbellatum). As explained above, it leads our never-plant-this list.

 

Here and next: Spanish bluebells (Hyacinthoides hispanica).

Here and next: Spanish bluebells (Hyacinthoides hispanica).

Spanish bluebells (Hyacinthoides hispanica) is very similar to English bluebells (H. Non-scripta) in behavior as well as looks (Spanish bluebell flowers hang to all sides from the stem; English bluebell bloom stalks are one-sided). Both spread aggressively and form such tight clusters of bulbs that other plants can be choked out.

Spanish bluebells (Hyacinthoides hispanica) is very similar to English bluebells (H. Non-scripta) in behavior as well as looks (Spanish bluebell flowers hang to all sides from the stem; English bluebell bloom stalks are one-sided). Both spread aggressively and form such tight clusters of bulbs that other plants can be choked out.

This bluebell-painted fern combination has been working for over ten years. The ferns arise later than the bluebells and cover for the bulbs’ exit – this photo was taken 4 weeks after the bulbs bloomed; some brown remnants remain. However, the bluebell colony is increasing. One day the gardener will be forced to referee.

This bluebell-painted fern combination has been working for over ten years. The ferns arise later than the bluebells and cover for the bulbs’ exit – this photo was taken 4 weeks after the bulbs bloomed; some brown remnants remain. However, the bluebell colony is increasing. One day the gardener will be forced to referee.

Have advice to share?

A name to add to our list, or a technique that works to stop a self sower? Tell us at the Forum in Invasive Bulbs.

Star of Bethlehem (Ornithogalum umbellatum) is not nearly pretty enough to make up for the harm it does in a garden. Its species epithet, umbellatum, refers to the arrangement of flowers on spokes from a main stem.

Star of Bethlehem (Ornithogalum umbellatum) is not nearly pretty enough to make up for the harm it does in a garden. Its species epithet, umbellatum, refers to the arrangement of flowers on spokes from a main stem.

The USDA site plants.usda.gov, is a good clearinghouse of information on plants growing in North America. It includes a “Legal Status” page for those plants like star of Bethlehem that have been outlawed or earned listings in weed textbooks.

The USDA site plants.usda.gov, is a good clearinghouse of information on plants growing in North America. It includes a “Legal Status” page for those plants like star of Bethlehem that have been outlawed or earned listings in weed textbooks.

Invasive plant societies also weigh in on plant character. Before you add a perennial species to your garden you can check the plant’s character. Be sure to notice any regional behavioral differences such registries indicate.

Invasive plant societies also weigh in on plant character. Before you add a perennial species to your garden you can check the plant’s character. Be sure to notice any regional behavioral differences such registries indicate.

Group 3: Others that warrant a cautionary note

Drumstick allium (A. sphaerocephalum) and blue allium (A. caeruleum). We know one species cannot change into another in a garden but in several instances it has seemed to us that drumstick- and blue alliums morphed into wild onion (Allium tricoccum). Probably it just happens that wild onion is able to more easily sneak in when it can hide among another self-sower's foot-tall, thin, onion-y foliage.

At any rate, fighting wild onion is such a chore that we have taken drumstick- and blue allium off of our desirable plant list even though we truly love their look. Now, we simply admire photos and plantings in other people’s gardens of these species’ red-violet egg-shaped blooms and blue globes rising above low growing perennials in June.

We did love to use the red-violet drumstick allium (A. sphaerocephalum, here rising above tall sedum and backed by Russian sage)...

We did love to use the red-violet drumstick allium (A. sphaerocephalum, here rising above tall sedum and backed by Russian sage)...

…and blue mini-globes of A. caeruleum, but too often it seemed the garden was then prone to subsequent invasions by wild onion (A. tricoccum). We decided the formers’ pretty presences could not make up for the risk of letting their weedy relative slip in.

…and blue mini-globes of A. caeruleum, but too often it seemed the garden was then prone to subsequent invasions by wild onion (A. tricoccum). We decided the formers’ pretty presences could not make up for the risk of letting their weedy relative slip in.

Some of the Asiatic lilies can become pests, as can giant allium (Allium giganteum) if the environment suits them. Although this is really no different than what some daylilies and groundcover perennials do, it can gall the gardener more because these bulb plants “hide” for part of every year (they go dormant). That prolongs the battle and makes it tougher to see and remove the unwanted excess.

More about star of Bethlehem in What's Coming Up 34. Download the pdf magazine to read page 8.

Which oriental lilies are invasive? Beats us. We try to predict which will spread like weeds and decide it’s the down-facing hybrids only to run into trouble with an up-facing variety. Fortunately, if we remain aware of the risk and on guard it is possible to remove troublemakers before things get too bad.

Which oriental lilies are invasive? Beats us. We try to predict which will spread like weeds and decide it’s the down-facing hybrids only to run into trouble with an up-facing variety. Fortunately, if we remain aware of the risk and on guard it is possible to remove troublemakers before things get too bad.

Most gardeners will say, “Pshaw, it not only isn’t invasive, we have to keep replacing the bulbs as they peter out.” All true. But where conditions are right – we have never pinned it down but silty soil and fertility might be keys – giant alliums can become downright pests.

Most gardeners will say, “Pshaw, it not only isn’t invasive, we have to keep replacing the bulbs as they peter out.” All true. But where conditions are right – we have never pinned it down but silty soil and fertility might be keys – giant alliums can become downright pests.

Are there others?

Probably! Wish we could live, garden and learn for 1,000 years - and keep reporting. Because we would surely discover new plant uses and abuses every year.

Watch in catalogs for the words "naturalize", "aggressive", "spreads readily". When you see these words, check further in Extension bulletins from .edu sites and .ext sites. Better to know something is questionable and give it a probationary try than to find out one spring that you’ve become the one waving the caution flag to others.

We’re sorry you can’t join us for the live webinars, B.T. We have fun and the feedback says the information is very useful. All subscribers do have the option of viewing the recordings at their leisure. To subscribe: https://gardenatoz.org/about-us/webinars-appearances-calendar/view-webinars-subscribe/#subscribe

 

Have advice to share?

A name to add to our list, or a technique that works to stop a self sower? Tell us at the Forum in Invasive Bulbs.