Rose of Sharon 'Aphrodite in full sun Northern California?

I planted two of these Rose of Sharon 'Aphrodite Oct 2009 (less than 2 years ago). They have grown a few INCHES and have a lot of yellow leaves.

In Feb 2006, i planted two Rose of Sharon 'Hollandia and they are doing great. They are about 12 feet tall and blooming continuously.

This is in the same yard as the "Aphrodite, same soil, same drip system, same amount of sunlight. I know that the 'Hollandia has a three year head start but if I recall correctly they were doing much better at 2 years.

Here is a picture of one of the Rose of Sharon 'Aphrodite Oct 2009 (less than 2 years ago). It is about 3 feet tall now and grew about 4 inches this year.

Here is a picture of one of the two Rose of Sharon 'Hollandia I planted in Feb 2006 and they are doing great. They are about 12 feet tall and blooming continuously.

Here is a picture taken in 2008 of one of the two Rose of Sharon 'Hollandia I planted in Feb 2006. This is TWO years after planting just like the last two I planted.

Big difference in growth. After 2 years the first two 'Hollandia are as tall as the fence. The last two 'Aphrodite is half as tall as the fence.

My posting here makes me feel like I'm talking to myself. I made the original post and the three replies. All by myself!

Must be getting old...I'm talking to myself. Self, we have to figure this out ourselves!

You might just need to give it a little more time--there's a saying "first year they sleep, second year they creep, third year they leap" that applies to many shrubs & perennials. Some will take off faster than that, but some take more time. The yellowing leaves are something to look at more closely though--could mean too much or too little water. Just because they're near each other in the garden & they're on the same drip system doesn't mean conditions are actually identical. Could be the new ones are slightly higher up or slightly lower down, or the soil drains slightly better or worse, or get slightly more or less sun...some combination of those factors could cause some differences. Could be there's a different number of emitters around the newer ones, or maybe a dripper got clogged so it's not getting as much water as you think it is. Also plants that have only been in the ground a year or two will often need a little bit more water than something that's had more years to get established. Lastly, I don't know anything about Hollandia or Aphrodite, but it's possible that Aphrodite is not as big a plant as Hollandia in which case it'll grow slower and never get as large.

I will never claim to know anything about growing plants in CA, but I'll offer some ideas about the performance differences - and recommendations when posting if one expects a reply.

Tell us what condition the plants were in when you bought them, and how you planted them. You've provided neither.

One of the major causes for poor plant performance in the landscape is poor quality plants when purchased. Rootbound container plants ranks near number 1. With no other info from the original poster, that's what I think the problem is.

Thanks for the replies. The soil and drainage conditions are the same. The drippers are about the same. Both varieties are supposed to grow to the same size. V.V., I purchased both from probably the best nursery in Sacramento and I believe they were Monrovia brand. They cost about $40 each in 5 gal. and not root bound.

My concern was maybe the 'Aphrodite doesn't do well here.

If you purchased them from an excellent nursery, then you obviously have faith that this vendor would not sell you a bad plant - nor a plant that would perform poorly. However, note to all: good growers are affected by the poor economy and slack times just like not so stellar growers. It is not outside the realm of possibility that plants were not moved along in the production process as well as they might be in better times.

Hibiscus syriacus 'Aphrodite' is an essentially seedless US National Arboretum selection that has been in the nursery/landscape trade for decades (since the '80s), and has been tested in growing zones across the US. If Monrovia produced it (fine CA establishment), then there's a kudo for use in your part of the world.

http://www.usna.usda.gov/Newintro/hibiscus.pdf

If you have not consulted this firm for their experience with the plant, then that would be my first step. Second, I'd seek out others that they've sold this plant to, and see how it has done for them. Also, check gardens/arboretums in your area (UC-Davis has a fine display area) and observe this plant's performance there.

If all these avenues of investigation show good performance for 'Aphrodite', then you have some problem at your location that just isn't obvious. I am not aware of any deathly difficulties that this plant has in the midwest, but our gardening conditions are in no way similar to yours. Your county's cooperative extension service may be a good source of information about how this species performs in your part of CA.