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Why and When You Need to Plant Spring-Flowering Bulbs in Fall

Seeing those first green leaves pop-up out of the ground in the spring, followed by the cheerful, brightly colored petals of tulips, daffodils, and hyacinths, is like taking the first bite of decadent waffles piled with fruit, syrup, and whipped cream, after weeks of plain oatmeal. Those bright flowers and signs of spring rejuvenate your senses after a long winter.

The best part about those vibrant harbingers of spring is that they appear almost by magic. They’re genuinely a set-it-and-forget-it gardening stalwart. But, those spring blooming flowers need to be planted in the fall. So, you do need to plan a bit for your “setting and forgetting.”

Why Do Spring Flowering Bulbs Have to Be Planted in Fall?

Spring flowering bulbs, like tulips and daffodils (and many others, we’ve got a list for you!) require a period of vernalization to bloom well during the growing season.

What the heck is vernalization? We’re glad you asked. Vernalization is the process of exposing seeds or bulbs to low temperatures for a period of time, to shorten their growth time before flowering. Basically, some plants need cold temperatures to kickstart their growing, and to make them bloom better. Vernalization also has some other positive effects, like shortening the vegetative phase of growth, improving blossom size and longevity, growing stronger and longer stems, enhancing resistance to cold and increasing resistance to fungal diseases. Each kind of bulb has a particular length of time that it needs to be exposed to its specific preferred temperature for the best results. You don’t need to worry about this too much, but the information is usually available on the package if you’re interested. It’s there for gardeners in warmer zones who have to refrigerate their bulbs. Luckily, here in Allentown, we can rely on winter to do this chilling for us, so we don’t have to fill our fridges with the flower bulbs we want to grow. We just pop our bulbs in the ground in late fall, and then we get to enjoy the surprise of beautiful flowers in the spring.

When Should You Plant Spring Flowering Bulbs?

Using “fall” as your time to plant spring bulbs is pretty vague. Fall in Pennsylvania is a beautiful season, and it can be reasonably long. If you plant your bulbs too early, say in late September, there’s a good chance your bulbs will put leaves up above the ground. You want your bulbs to conserve their energy for putting up leaves in spring. Planting them early, in warm soil, with lots of warm air, and a good drink will encourage them to grow fast. Waiting until the weather has cooled down will slow down how much they grow, so they should just have time to produce a sturdy root system before the ground freezes hard. If you want to be precise, you can monitor air and soil temperatures to decide when to plant your bulbs. Usually, when air temperatures are consistently around or under 50ºF, and soil temperatures are at or below 55º, you can start planting your spring-flowering bulbs. If you don’t have a soil thermometer, you can use a meat thermometer, just make sure to push it into the soil as deep as you can, leave it for a couple of minutes, and wash it thoroughly. As a general rule of thumb, however, you don’t need to measure soil temperatures. You just need to keep an eye on the weather. The average first frost in our area is in mid-October. Anytime around the first frost is a good time to plant bulbs. If the weatherman is calling for the first frost of the season, plant your bulbs that week.

Don’t panic about getting your bulbs in the ground before the first frost. You can still plant them even after the first frost has happened. The ground won’t freeze solid for a few weeks yet, so just get to it when you can, from mid-October through November. Spring flowering bulbs are surprisingly resilient, so they can be planted in very chilly ground and survive. With that said, it’s much easier to plant them before the soil freezes, so try to get it done before November ends.

How to Plant Spring Flowering Bulbs?

There are three basic guidelines for how to plant spring-flowering bulbs:

  1. Plant them 3 times as deep as the bulb is tall, and space them 2 times the bulb height apart. So if the bulb is 2 inches tall, plant them 6 inches deep and 4 inches apart.

  2. Plant them pointy end up. The leaves and buds come out of the pointy end. So, to make growing easy, set them in the hole facing up. They’ll likely still come up even if they get flipped upside down. It might just take a little longer than expected.

  3. Water them well, once. Because bulbs are planted fairly deep, you’ll need to give them a good slow soak to get the water all the way down to the bulbs. This first watering will help them start to grow roots.

And then you walk away and forget about them until they show up in the spring.

What Spring Bulbs Should I Plant In Allentown?

Allentown is USDA Zone 6B, so we’re pretty lucky in that we can grow a huge variety of bulbs. Our winters are still cold enough to provide vernalization, but warm enough not to kill some of the less hardy bulbs available. If you plan out your planting, you can have bulbs blooming through the last snow, all the way into early summer. Planting for sequential blooming is easier than you think. Here are the bulbs we can grow in zone 6, sorted by when they bloom. Simply choose a few from each blooming period, and you’ll get to enjoy pretty bulbs through all of spring.

Planting Spring Bulbs for Sequential Blooming

Some of the early spring-blooming bulbs you can plant are:

  • Snowdrop

  • Hyacinth

  • Spring Snowflake

  • Crocus

  • Daffodil

  • Tulip

Flowers like daffodils and tulips have been bred extensively. Varieties have been adapted for early, mid, and late spring blooms. So if you really like tulips or daffodils, you can have them blooming through spring by planting several different varieties.

For mid-spring blooming bulbs, you can plant these flowers:

  • Daffodil

  • Hyacinth

  • Tulip

  • Lily-of-the-Valley

  • Spring Starflower

  • Iris

  • Fritillaria

For late-spring blooming bulbs, you can plant these flowers:

  • Allium

  • Bluebells

  • Tulips

  • Lily-of-the-Valley

  • Peony

  • Irises

  • Anemones

Ready to fill your flower beds with anticipation for a riot of colorful blooms next spring? Stop by our garden center today, and browse through our large selection of different spring-blooming bulbs to plant this fall.

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