Question: Is it necessary to divide spring bulbs or will they spread on their own?
Spring flowering bulbs are so popular, in part, because they require very little maintenance. Once you've dug the holes and planted them in the fall, you can almost forget about them until they pop up and flower, the following spring. As the planting matures, the bulbs will divide and spread on their own. But eventually, the planting area may become crowded and produce fewer flowers, instead of more.
Should you divide and replant these bulbs or just replace them?
Answer: Crowded bulbs will start to flower less prolifically and the original bulbs will eventually give out, but that doesn't mean you need to start all over again with new bulbs. Spring flowering bulbs can be dug and divided, just like most other flowering plants. The real question becomes: do you need to divide spring-flowering bulbs and, if so, how often?
Do You Need to Divide Spring Flowering Bulbs?
That really depends on the type of bulb and how well it is growing. Daffodils will live for generations without any help from us. Others, like tulips, tend to fade out after a few years. A good rule of thumb is to watch how well the bulbs are blooming. If an established patch of bulbs starts to bloom less and less or begins blooming sparsely, the bulbs have probably become over crowded. That's the signal to dig and divide.
How Often Should You Divide Bulbs?
You can divide your bulbs before they start to decline.
Every 3-5 years should be sufficient to give you enough new bulbs to keep your patch in bloom. Just keep in mind that it will take a couple of years before the tiny offset bulbs have built up enough energy to begin blooming.
If you don't want to renovate an entire planting and miss a season of bloom, you can always plant the small bulbs in a separate area or holding bed for the first couple of years and then transplant to the border when they are large enough to bloom.
How to Divide Bulbs
The first step is lifting the bulbs from the ground. Always dig the bulbs, don't try to pull them up by the foliage.
The best time to move bulbs is when the foliage is just about gone; the plant is no longer actively growing, the bulb is recharged and you can still see where they are. Take care when digging that you don't damage the bulbs themselves. Remember that bulbs tend to pull themselves deeper than they were originally planted and spread out. So start digging a few inches away from the plants and wait until the bulbs are loosened - don't pull on the leaves.
To divide bulbs, carefully pull the small bulbs from the base of the plant. The larger the small offset bulbs are, the sooner they will flower. Check the original bulb for firmness. If it appears in good health, go ahead and replant it; you may still get several years of flowering. If it appears shriveled or damaged, toss it.
Re-planting Flowering Bulbs, After Division
You can plant all the small offsets. They may appear small now, but giving them adequate spacing at this time will save you the effort of re-digging and re-panting in a year or two. Or, as mentioned above, you can plant them in a holding bed and move them to a permanent spot once they've had a couple of years to mature.
You could also store your bulbs until it's time to plant in the fall. If you chose to store the bulbs, be sure to remove all the soil and allow them to air dry for several days. Remove any injured or diseased bulbs and any that feel soft. Then store in a mesh bag or in some dry peat moss. Keep them in a ventilated, but cool, dark spot and check periodically during the summer, to make sure they are not rotting or drying out. Replant the following fall. Sources:
- Ohio State University Extension: Growing Hardy Bulbs
- Sunset: How to Divide Bulbs
- University of Illinois Extension Bulbs and More