University of Vermont
Department of Plant and Soil Science
SPRING-FLOWERING BULB QUESTIONS
Dr. Leonard Perry, Horticulture Professor
University of Vermont
Fall is the time to fast-forward and plan for spring, at least in terms of
planting spring-flowering bulbs such as daffodils and tulips. They’re
easy, and will be a welcome sight next spring coming off of our typically
long winter. Here are ten common questions you may have on what to
plant, and how to go about it.
Q. Are there any bulbs that are deer resistant? Although deer may eat
anything if they are really hungry from lack of other food, or there are too
many deer for a given area, they almost always leave daffodils alone.
That’s the main reason I began planting so many years ago. They
contain calcium oxalate crystals, which cause a burning sensation when
Daffodils also contain a toxic alkaloid “lycorine”. A bite of the
plant causes stomach upset, but quantities can be toxic to not only deer but
also to cats, dogs, horses, and humans. Other bulbs that may be deer
resistant include crocus, ornamental onions (Allium), squill,
glory-of-the-snow (Chionodoxa), grape hyacinths, and snow
drops. Interplanting tulips and daffodils may be effective in training
deer not to browse.
Q. What bulbs are most hardy? Most spring-flowering bulbs are hardy
throughout our north country, except for some of the species tulips.
English bluebells are less hardy than their Spanish relatives.
Q. I’ve had tulips in the past, but they haven’t lived and bloomed
more than one year. What did I do wrong? You did nothing wrong,
as this is the nature of most tulips—treat them as gorgeous annuals for
their spring beauty. There are some tulips—hardy species ones and
Darwin hybrids in particular—that are perennial and will return and bloom
for several years. Look for
such in the bulb descriptions.
Most tulips need specific conditions to rebloom, as they have in their
native Turkey and central Asia—hot and dry summers. Even then, the
tulips you buy have been grown for several years in Holland to their peak of
maturity, and they split into many baby bulbs right after bloom.
Q. I have shade and wet soils. Are there any bulbs that I can
grow? Bulbs really need soils that don’t stay wet. Checquered
lily (Fritillaria meleagris) is an exception that tolerates soils
that are wet or periodically flooded. Otherwise, consider a different
site or berm.
Bulbs grow and bloom best in full sun, but there are some that tolerate part
(four to six hours of direct sun) to full shade. Those that bloom
early in spring, such as snowdrops, squill, and glory-of-the-snow, can make
sufficient nutrients and will die back as leaves come out on deciduous trees
(such as maples and oaks). Other good choices for part shade sites
include the checkquered lily and bluebells or wood hyacinths. The low,
yellow woodland tulip (Tulipa sylvestris) also grows well in sun or
Q. Each year squirrels, rodents, and small mammals such as skunks dig up my
bulbs. How can I prevent this? First, try some granular animal
repellents you can buy and sprinkle around your plantings. Try
liberally sprinkling ground shells or rocks (you can buy such in the poultry
area of feed stores, or even in garden stores for bulb planting) in planting
holes or beds, along with the bulbs. When critters dig and reach these
sharp bits, this often discourages them. Finally, if using a permanent
bed for planting each year, such as with their favorite tulips, line it
first with wire mesh such as hardware cloth or poultry mesh, then cover it
with the same (just remember to remove hardware cloth when bulbs sprout in
Q. How close and deep do I plant bulbs? Generally, plant about
two to three times the bulb diameter in depth. So the top of a tulip,
hyacinth, or daffodil bulb, a couple inches wide, should be planted about
five to size inches deep. Plant smaller bulbs such as crocus,
snowdrops, or grape hyacinths with their tops about two to three inches
Spacing depends partly on your budget, partly on the effect desired.
If you want a more showy effect sooner, plant bulbs closer. On
average, space tulips about four to six inches apart, daffodils six to eight
inches apart, and small bulbs (like crocus) three to four inches
apart. Tulips are formal, so best planted in even numbers, in formal
rows, and in masses (rather than a straight line). Daffodils are
informal in effect, so best randomly arranged and spaced throughout a bed or
Q. Do I need to add fertilizer when planting bulbs and, if so, why kind and
how much? Bulbs already contain nutrients for the coming year, so if
you’re just planting tulips for a one-time show, fertilizer really doesn’t
help. But, if you’re planting perennial tulips, daffodils, or other
perennial bulbs, add a source of phosphorus (such as superphosphate or
natural rock phosphate). Phosphorus is needed for root growth, and
doesn’t move much in the soil so needs adding at planting. Best is to
use a bulb fertilizer formulated just for them. Best is not to use
bone meal, as it attracts skunks and other mammals.
Don’t use too much fertilizer, as it can burn the base of the bulb. If
planting bulbs such as daffodils individually in holes, only use a quarter
teaspoon or so of fertilizer. If a larger bed, use about
one-quarter cup per 10 square feet. Make sure to work the fertilizer
in, and place a layer of soil between it and the bulb base.
In subsequent years, fertilize in late summer or early fall when bulbs are
making roots. You can sprinkle bulb fertilizer on the surface then,
according to label directions, or water bulbs with a liquid fertilizer high
in phosphorus (the middle number on the fertilizer analysis).
Q. Bulb leaves look unsightly in spring after bloom. Can I cut
them off? Not if you want bulbs the following year, as that is when
they’re making nutrients for that next spring. You can “trombone” them
if just a few, bending the leaves double and holding with a rubber
band. Or, as they die back, you can cut them back by half. If
you’re worried about their looks, interplant among other perennials that
will hide the dying bulb foliage as the perennials grow.
Q. I’m behind in my gardening. How late can I plant bulbs?
Spring-flowering bulbs need about six weeks to root in the fall, so they
don’t frost heave in the spring, and have roots when the tops begin growing
then. Bulb roots tend to grow until about early November in colder
climates. So, this means mid September to early October is the best
time to plant there. Plant too soon, when the ground is still warm,
and bulb tops may start to grow. Even if you’re late planting them in
the fall, this is better than trying to hold bulbs until spring—they’ll
start growing then before you can get them planted, and they need winter
cold to form flowers.
Q. How do I go about “forcing” spring bulbs in pots for spring
bloom? Bulbs need 10 to 12 weeks of cold (40 degrees F or lower, but
not freezing too severely), to form blooms next spring. If you don’t
have such in a cellar, coldframe, or old refrigerator, you can pot the bulbs
(plant three daffodils or four tulips in a pot 6-inches wide), then bury
them in the ground, pots and all. Pot rims can be at the soil surface
or slightly below. Then add a few inches of bark or straw mulch.
Use soil or compost for mulch instead if you have rodents. The
advantage to using a cold space indoors is that pots are much more
accessible earlier in the spring than if they’re buried and frozen in the
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