Petal Count

Hey all,

Still trying to get some things straight in my mind prior to beginning my first endeavor this Spring.

My question relates to petal count. Can someone please explain to me how this works? What trait(s) is dominant?

For example, if I cross a 25-30 petal rose such as Honor with a 50-65 petal rose such as Pink Peace, what ratio can I expect on the petal count of the offspring (generally speaking). Example 2: If I cross a 25-30 petal with a 5 petal rose what can I expect?

Thanks for the help. I really appreciate everyone taking the time to help me get a better understanding of this.


P.S. I read Jadae’s post on ruffled petals. Very interesting. The Forum is very helpful especially to someone like me who has a ton of questions.

Hi Melanie:

That’s a good question. No doubt, petal count is genetically determined. Generally speaking roses with fewer petals crossed with roses with fewer petals will produce roses with fewer petals. You can also expect roses with more petals crossed with roses with more petals to produce roses with lots of petals.

In my experience petal count is neither dominant nor recessive. In the above examples, you can get roses with lots of petals from the first example and you can get roses with fewer petals with the second example.

So, just cross roses that have traits that you desire to combine and see what you get. If you are looking for single petalled varieties, however, you will have better luck crossing singles with singles.


Dr. Walter Lammerts, who bred Chrysler Imperial and Queen Elizabeth, wrote that doubleness seems to be dominant and quantitative, i.e., that the more ‘doubleness genes’ a rose inherits, the more double it is. It may be more complicated than that. There may be one gene that determines whether or not a rose is double, and other genes that determine how double it is.

The additional petals are transformed stamens. (Sometimes you’ll see a partial anther on an inner petal of very double rose due to incomplete transformation of a stamen to a petal.) There may be one gene that allows the transformation of stamens into additional petals, and other genes that control the number of stamens and therefore how many are available to be transformed.

I think that it is important to distinguish between true singles (5 petalled roses) and nearly single (5-8 petalled) roses. It seems to me that nearly single roses behave more like double roses than single roses in crosses. For example, Lilac Charm is considered a single, but can have up to 8 petals. When you self Lilac Charm, you get some quite double seedlings.

If doubleness is dominant, then crossing two 5 petalled roses should always give you 5 petalled seedlings. I tried that experiment last summer, but don’t have the results yet. Perhaps someone else on the forum has tried it? In any case, Jim Sproul’s strategy of crossing roses with the traits you want seems to be the best bet. If you want singles, cross two singles. If you want doubles, cross two doubles.

This article by Dr. Lammerts describes his observations on dominant and recessive traits:


About roses genetics we have to consider two facts: most are tetraploids hence with four similar genes and as much as 3 recessive for each dominant.

Quantitative or dominant heredity is much complicated by this fact.

Even more when we consider that many gametes (as much as 100%) are sterile and/or eliminated.

Prediction of the progeny’s characters is only from experimentation.

Modern complex hybrid roses hability to transmit qualities is very very weak.

Most commercial breeders raise as much as 100,000 seedlings for each selected var. And most of said vars are no improvements.

Nevertheless raising your own roses is quite addicting.

Friendly yours

Pierre Rutten

Hmm? I have grasped that the variable(s) of certain gamettes being eliminated certainly makes this a much more complex endeavor to say the least. I did not realize that some of the gamettes would be sterlie though.

Still, even if there are 3 recessive for each dominant, the dominant gene will prevail – yes? However, if this was the condition, we would lose any chance for quantitative properties. Please let me know if this line of thought is correct.

The more I learn, the more “hit or miss” this really seems. Somehow that just sort of goes against my grain. There should be a way to make this more clear cut. Hah! I chuckle here because I’m sure every person who’s ever tried hybridizing has said the same. Now if we could just figure it out! Then again, that would probably just take some of the fun out of it.

Thanks for your help and for letting me share my thoughts with all of you.


Melanie, you are correct that a dominant gene will prevail even if there are 3 recessives.

I think that Dr. Lammerts’ was incorrect when he conjectured that the “doubleness gene” was quantitative. One reason is that I got some singles when I crossed two very double diploid roses, Mons. Tillier and Duchesse de Brabant. Since some of the seedlings were singles, both parents must be heterozygous for the doubleness gene, i.e., each parent has one copy of the dominant gene and one copy of the recessive. Since both of the parents are very double in spite of having just one copy of the doubleness gene, it doesn’t seem to me that the doubleness gene can be quantitative. I think it is more likely that the doubleness gene merely determines whether or not the flower is limited to 5 petals, and that one or more other genes determines the quantity of petals. Those other genes may be present in singles, but would have no effect if the number of petals is limited by the recessive version of the doubleness gene.

Dr. Lammerts was the first to try to put rose breeding on a scientific basis. He and others have made progress, but it is still mostly a mystery. But trying to figure out the mysteries is one of the things that makes rose breeding fun!

I was once asked by an individual at an RHA meeting why seedlings from the same cross and even from the same hip were so different. When I asked him how many children he had, he replied six. I then asked him if they were all alike. The look on his face told me the answer.

We have seven seedlings from one hip growing in one of our test beds and the blooms range from 5 petal whites and pinks, a 40+ petal white grndiflora, a yellow blend HT, and a pink floribunda. Hybridizing has to be one of the most fun “crap-shoots” that one can engage in!


Guess I better keep really good records huh?

Melanie - Yes, it really helps to keep good records. In that regard you can work on building a line up over several generations by keeping those that display the characteristics that you want to perpetuate. No guarantees on what results you may eventually end up with but it saves a lot of time going over the same ground again and again.

Sounds like you are having fun anyway - keep up the good work and the thought provoking questions here on the forum. It makes it a very good learning experience for all of us to read the varied posts from a lot of folks.