Hydrangea no flowers

I have a hydrangea that is about 10 years old I think but it never really flowers - think we got two blooms last year and none at all this year. The foliage looks lush and healthy. I think these flower on old wood? So I pruned it very gently early Spring but nothing. I have tested the soil it is alkaline but I think that affects the colour of the blooms (if you get any that is). It is right next to a white hydrangea panticulata (see bottom front left of photos) which flowers abundantly and gets bigger and better every year. What am I doing wrong? Not sure whether to feed it or what with?

 

It is a hydrangea macrophylla, also known as a big-leaf hydrangea, a French hydrangea or hortensia. Macrophyllas produce two types of blooms: mopheads and lacecaps. There are two "versions" on the market. One version -like you mentioned- produces blooms only in early Spring from old wood. Those flower buds open in Spring but, the plant develops them at the end of the stems in July-September of the previous year. So the pruning that you did in early Spring cut off the blooms for this year. The other version, called a "rebloomer" in most commercial ads, produces blooms twice. The second flush happens in mid to late Summer but those blooms from the 2nd flush originate only from the new stems that start growing in the Spring. If those new stems are able to get tall and old enough before the plant goes dormant, it will quickly develop flower buds and quickly open the blooms.

I normally do not need to prune the hydrangea except to remove dead stems that do not leaf out by the end of May. Mother Nature usually takes care of deadheading the flowers (or I will). You can deadhead spent flowers at any time as long as you do not cut the stems. The flower buds are inside the stems protected from winter so it is hard to know where to cut. As a result, I tend to cut the peduncle, a string that connects the bloom to the stem.

The plant looks well established so no fertilizing is actually needed. Hydrangeas are not heavy feeders like roses so after 1-3 years, you can discontinue fertilizing them as long as you maintain 5-10cms of mulch year around and as long as your soil has no mineral deficiencies (like sandy soil, etc.). They will feed off the decomposing mulch in later years and use it to protect the roots from temperature extremes. In early Spring, I feed my new ones cottonseed meal, organic compost or composted manure. That is it for the whole year. You can also use a general purpose, slow release chemical fertilizer (per label directions) with a NPK Ratio of around 10-10-10. Do not use any fertilizers, even weak ones (like coffee grounds, liquid fish, liquid seaweed, etc) three months before your average date of first frost as you want the plant to be able to go dormant at the proper time and not be in "grow mode" late in the growing season.

Other causes of blooming issues with macrophyllas include using a fertilizer that has too much nitrogen, fertilizing too many times, fertilizing close to early frosts in the Fall, dense shade, very cold winter temperatures (water deeply and winter protect), late frosts (water deeply; cover the plant and-or winter protect), lack of water during winter and pests like deer/squirrels/bunnies/etc.

 

Thank you Luis for the very detailed reply. I will give that all a try. If I get any blooms next year I will certainly post a picture on here.

 

Thank you @luis_pr ... that helped me too as i have three macrophylla with a total of 3 blooms between them.