In contrast, some old garden roses and climbing roses bloom once a year or bloom only in the spring and fall. Roses that bloom on a regular basis are called “repeat” bloomers.
The speed with which a rose (1) forms a new bloom-producing cane (stem) (2) develops a bud, and (3) the bud opens to a flower varies. When we cut off a dead spent bloom (deadheading) we signal to that stem to grow a new flower-producing stem. In repeat-blooming roses, the timing of the blooming process begins with the removal of an aged flower.
Generally it takes 4 to 10 weeks (28 to 70 days) for reblooming to occur. Roses having a lot of petals take longer to re-bloom than roses with only a few petals. Miniature roses, single roses (those with 5 to 12 petals) and some old garden roses (especially Chinas, noisettes and polyanthas) tend to re-bloom the fastest (28 – 32 days). Roses with a lot of petals (45 – 50) take longer to re-bloom, usually 6 weeks. While densely-petaled roses like Belinda’s Dream and Quietness (100+ petals) take the longest to rebloom, these roses hold their blooms on the bush a lot longer than their lesser-petaled counterparts. It is common for 100-petaled roses to last on the bush 10 to 14 days, making it worth the wait from a landscape impact perspective. A good rule of thumb is “more petals = more time.”
If you are planning a garden event where it is important to have a big floral impact on a certain date, you can even refine these general guidelines further to help your roses be in bloom for your event. Several months
before your event, when you remove a spent bloom from one of your bushes, write the
date that you cut the stem a plastic bread wrapper tab (Figure 1). Hook the tab on the cut stem on the rose bush. As soon as a new bloom forms and opens, calculate the number of days it took for that bloom to develop. This will allow you to count backwards from the date of your event for the number of days it took that rose to re-bloom. That number tells you how many days before the event you will need to groom and deadhead the bushes. Repeat this process on the different varieties of roses in your yard. To ensure a staggered bloom-out, groom your bushes over a 2 week period. This will help ensure that you will have a continual flow of color during the week of your event.
By knowing these blooming tidbits and staggering the deadheading process it is possible to ensure that your roses continually have flowers throughout the growing season.