Limelights get very large so I would not consider them good candidates for potting. But Little Lime, a dwarf version, could be a better choice for containers.

Find a location that gets shade during the summer months and plant them in the ground instead. During the early Spring, they can get full sun with no damage to the leaves because the sun is not as strong as it is during the summer. You can also place them where they get dappled sun. If the area is windy, that may speed up drying of the soil of consider an alternate place or block the wind somehow. A 35% shade cloth can be used in some locations.

The soil should be well draining and acidic. If your soil is alkaline, use lots of compost mixed in with your soil. Hydrangeas will tolerate some alkalinity but only up to a point so, if the soil is alkaline, acidify the soil in Spring every year (be aware that you may have to acidify again later on). I acidify in Spring every year and again if I noticed signs of iron chlorosis. So on some years, I have to amend the soil again in July-September.

You can add fertilizer in Spring, a few weeks after your average date of last frost. You can use 1/2 cup to 1 cup of cottonseed meal, compost, composted manure or a general purpose slow-release chemical fertilizer like Osmocote 10-10-10. During the rest of the growing season, you can also apply some coffee grounds, liquid seaweed or liquid fish. Cease fertilizing by the end of June to make sure the plants will go dormant in the Fall.

You can probably start watering by adding 1 gallon of water per watering. To know when to water for sure, use the finger method daily for 2-3 weeks: insert a finger into the soil early in the morning to a depth of 4". Water if the soil feels dry or almost dry. Note the date when you watered in a wall calendar. After 2-3 weeks, review how often you watered (every 3, 4, 5, etc days). Then set the sprinkler to water 1 gallon every 3/4/5etc days. If the temperatures go up/down 10-15 degrees and stay there, consider using the finger method again for 2-3 weeks to see if you need to tweak things. Maintain 3-4" of organic mulch at all times to lengthen the number days between waterings; I check mulch levels in Spring and in the Fall. Once the plant goes dormant in the Fall, you can reduce waterings to once every 2-3 weeks. And if the ground freezes, you can stop altogether. Just remember to water during winters that are mild (warm temps; soil does not freeze) and dry.

I have not seen these bagged hydrangeas for sale here. You could grow them in pots but read whatever label comes with them to find some size estimates and information about winter hardiness. Most mopheads have trouble growing/blooming outside year around when you get to Zone 6. Assuming they bloom on old wood (they develop invisible flower buds in July-August), I would slowly grow them in pots (changing to a bigger pot size every 2-3 years). You will need to water/fertilize them more often when planted in pots and bring them inside a garage when they go dormant.

The bloom colors are a function of the acidity in the soil. Blooms that are originally white are not influenced by the soil acidity but pink/blue/purples are. Pink blooms require neutral to alkaline soil. Purples occur in a very narrow range of soil acidity (somewhere between acid and neutral) and are difficult to duplicate. Blues require acid soil. Aluminum sulfate is normally used to get blues when you have alkaline soil. Garden Line is used when you want pinks and the soil is acidic.

Hydrangeas get large and wide (6' high and slightly less on average for mopheads; more for Limelights) so they can be difficult to pair with other plants long term in a pot/container. I have not tried doing that but maybe a shrub that overhangs and falls down the sides of the pot may look nice. I would try annuals during the first few years.

Luis

This post was edited by luis_pr on Sun, Mar 31, 13 at 6:07