You normally do not need to prune hydrangeas, valtorrez, especially if your plants are that small. Instead of worrying about pruning, check some of the other things that could be causing few blooms (other than the plant size itself).

Add about 1 cup of cottonseed meal in June and sprinkle coffee grounds or weak fertilizers like liquid seaweed during the growing season. Make sure that the plants get some sun. Generally speaking, the more sun a plant gets, the better flower production is.

And maintain the soil constantly moist as best as you can. If a finger inserted to a depth of 4" feels almost dry or dry then water. About 1 gallon of water per week, applied to the soil, should be enough in Spring. Increase the frequency or the amount as summer approaches or as the plant gets bigger. And reduce the amount of water in the Fall. When the soil is frozen in Winter, do not water. But water somewhat during warm dry winters. About 3-4" of mulch should help keep the soil moist longer.

A soil test done once every 5 years (or so) is a good idea to make sure that your soil does not need extra doses of some minerals or soil pH amendments. Cheap kits are sold to give you an idea of how acidic or alkaline your soil is. Hydrangeas prefer acidic soil and will tolerate some alkalinity. Nearby local nurseries and neighbors might be able to tell you if your soil is acidic or alkaline.

Height is a genetic trait and varies depending on the variety of hydrangea that you have. Pictures of the blooms, leaves and stems are the usual ways of telling what hydrangea variety you have but, even then, some varieties are so similar that, it may not be possible to identify with 100% accuracy. Please post any pictures that you have to see if anyone can help.

Colored (blue/pink) blooms suggest that you probably have hydrangea macrophyllas, which come in two flavors: mopheads and lacecaps. Their flower buds develop starting in July-ish. Some macrophyllas develop blooms only once a year, around July, while others -like Endless Summer- develop blooms around July and again in Spring (or Spring & Summer).

When you do not know what variety of hydrangea macrophylla you have, you must prune carefully. If you prune NOW a mophead that blooms only once, you would be pruning away the Spring 2010 blooms. And you would not have blooms again until Spring 2011. So until you can identify the variety, if you have to prune, prune sometime after blooming but before the start of July.

In the case of a hydrangea like Endless Summer, pruning them now in March results in no early Spring blooms; but new ones will develop quickly so there is no risk of zero blooms during the complete growing season. Deadheading will encourage the plant to bloom again.

Last year's dried out blooms may start to disintegrate between now and May. The strings that hold them may now be brittle enough where they break just by applying a little pressure. If not, deadhead them or wait a month & try again...... I usually just let them fall to the ground on their own.

When you have time, go to the link below to read all about pruning all types of hydrangeas, fertilizing, etc.

Luis

Here is a link that might be useful: Pruning Information