I've spent years planning, designing, and planting to ensure my yard is colorful all year long. Part of my success is careful use of planters. If you stand at the edge of your yard in any season, you can tell where a splash of color would help, and that's where a planter can go.
And while you could keep replanting the contents of the planter as the seasons change, there is a surefire way to get months' worth of blooms while doing very little year to year: Plant bulbs instead. Not just a few bulbs—like your building a plant lasagna, you're going to layer the planter top to bottom with bulbs that will bloom at different times of year.
The time to get started on this project is now. In the early fall, atop your bulbs, you'll plant snapdragons, pansies, and flowering kale to keep the planters looking full until the bulbs come in.
Choose bulbs for each season
Bulb season lasts from late winter through the middle of summer, and bulbs all flower at different times within that range. Choose bulbs with different bloom times and you'll be able to extend the bloom time of your planter. Bulbs are designated late winter, early/mid/late spring, early/mid/late summer and early fall. I consistently return to this incredibly in-depth calendar from my local nursery—while the month-by-month timings are for the Pacific northwest, you can abide by the season designations on the left (early spring/late spring, etc). For example, using this chart, you could choose snowdrops, daffodils, tulips, lilies, and dahlia.
Again, your bulbs will carry you from winter through the summer, when you'll plant annuals for the fall while the bulbs underneath are exposed to the cold they need to bloom properly. It will be helpful to sketch out the planter and what you'll put into each layer, plus the corresponding bloom times, to help you visualize the results.
Plant bulbs at a depth three times their size
It's not hard to plan out your year of blooms and plant them accordingly. The bulbs all live under the soil in the depth of the pot. Generally, the rule for bulbs is that they should be in soil three times deeper than the height of the bulb. Bigger bulbs belong deeper in the planter, and as you progress upwards, you’ll continue layer in smaller and smaller bulbs. The larger bulbs need that depth to get the nutrients they need and to have enough room for their roots.
Choose the right size container for the bulbs
To ensure the layering works, you can’t overcrowd the pot, and it needs to be the appropriate depth. For these longterm outdoor planters, I always like to choose ones that are 24 inches tall or more, and at least 14 inches across. Make sure you choose planters that are weatherproof- terra cotta will not overwinter well. The more layers of bulbs you want, the deeper the planter needs to be.
Planter bulbs need more water and more insulation
As you're planting, make sure bulbs are not touching, but they don't need more than a few inches between them. The smaller the bulb, the more you can plant. Bulbs generally enjoy bulb-specific fertilizer each year, so as you plant, consider adding that to the soil mix. You should plant into a potting mix, not a soil meant for raised beds.
Planters generally, and by design, dry out faster and offer less insulation than the ground, so keep that in mind. Water your bulbs for a few weeks after planting, as they are forming their roots. Insulate for winter depending on where you live. Then ensure that your bulbs have water throughout the growing season—that means the soil should always be lightly moist two to three inches down, but never wet or dry.
Top your bulbs with annuals for fall and winter
Once the bulbs are in place, it's time to give the planters some color for winter. Your local nursery will have flowering kale, pansies, and other fall annuals that are cold hardy. Since these are planted into the topmost layer of soil, they shouldn't disturb the bulbs, and will give you color for the next few months, even as they insulate the bulbs.
