How the layers are worked out
The top layer goes in at its usual planting depth, measured to the base of the bulb, from Nebraska Extension's bulb table. The latest bloomers go lowest, and each layer sits an inch (2.5 cm) of mix below the one above, so lower layers can end up deeper than usual: tulips 10 to 11 inches down under daffodils and crocus, in line with the 8 to 10 inches Longfield Gardens gives. Rutgers Master Gardeners do it the other way: the bottom bulb at its own depth and the rest stacked above with an inch or two of soil between. The planner also leaves two inches (5 cm) under the bottom layer for roots and an inch below the rim for watering.
When a pot is too shallow for every bulb at full depth, the bottom layer moves up first and the others only as far as they must. You get a note when a bulb ends up shallower than its usual range.
Counts come from the extension rule for pots: a 6-inch pot holds six tulips, five daffodils, three hyacinths or 15 crocus or other small bulbs, almost touching. The planner scales that to your pot's width at each layer, so a tapered pot holds fewer bulbs lower down. In the ground it uses normal bed spacing instead.
Bulb lasagna questions
How many tulip bulbs fit in a 12 inch pot?
About 24 if they are almost touching, the way forcing pots are planted, and about 10 with half a bulb's width between them. That is for a straight-sided pot with the tulips 8 inches deep. A 30 cm pot holds about 22 or 10.
How deep does a pot need to be for a bulb lasagna?
For tulips, daffodils and crocus at their usual depths, about 14 inches (36 cm). At the shallow end of the ranges, about 12 inches (30 cm) works. Two layers, such as daffodils under grape hyacinths, fit in about 11 inches.
Which bulbs go on the bottom?
The ones planted deepest, usually tulips or large daffodils, and among those the latest to flower. Small early bulbs such as crocus and grape hyacinths go on top. The shoots from the lower layers grow up between them.
When should I plant a bulb lasagna?
In autumn once the soil has cooled below 60°F (16°C): late September through October in a cold-winter area like Nebraska, later where winters are mild. In the southern hemisphere that is late March to April.
Does a bulb lasagna pot need protecting in winter?
Pots freeze harder than garden soil. Keep bulbs off the pot wall, use a pot with drainage holes, and in a hard freeze move it into an unheated garage or shed, or use an insulated pot. Check now and then that the mix has not dried out.
Can I plant a bulb lasagna in the ground?
Yes. Choose Ground, enter the size of the patch, and the planner digs the layers to full depth at normal bed spacing: 6 inches for most tulips, 4 for daffodils and crocus.
How long do bulbs need in the cold before forcing?
UW-Madison Extension gives most bulbs 15 to 17 weeks at 35 to 45°F, hyacinths 12 to 15. Missouri Extension says most need 13 or 14 weeks, and Mississippi State gives grape hyacinths 8 to 12. Flowers follow 3 to 4 weeks after you bring them in. The Forcing indoors tab shows when a shorter time still makes your date.
Will the bulbs flower again next year?
Bulbs grown in pots are often treated as annuals. You can plant them out in the garden in autumn once the leaves have died down, but tulips in particular often flower poorly after the first year. Forced bulbs rarely rebloom.
Sources: Nebraska Extension G1742, Spring flowering bulbs; University of Missouri Extension G6550, Forcing bulbs; Iowa State Extension, forcing and planting depth; Penn State Extension, forcing; UW-Madison Extension, forcing bulbs; Mississippi State Extension P2730; Rutgers Master Gardeners, bulbs in containers; NC State Extension, potted bulb lasagna; University of Arkansas FSA2096; RHS, planting bulbs.