I would like to plant hydrangeas along a south-facing shed. The site gets some morning sun and quite a lot of afternoon sun from over the roof of the house. This area currently has moss growing on it and has not been previously used for planting. Your reply will help me to decide whether to plant there or not.
I have amended the area where I have planted the hydrangeas with chicken manure and compost. I dug holes about 14 inches deep and and about 14 inches square. I also put a spade full
Most hydrangeas will do well in sun to part shade although full sun in a hot climate would be too much. You also want to bear in mind that hydrangeas, especially Hydrangea macrophylla, prefer adequate moisture. According to Michael Dirr’s Hydrangeas for American Gardens (Timber Press, 2004), an inch of water once or twice a week should be sufficient as long as the plant’s soil needs are met (consistently moist, well-drained, acidic soil which is rich in organic matter such as leaves, compost, well-aged manure). Some species of Hydrangea tolerate heat better than others, according to Dirr. Hydrangea macrophylla, H. serrata, and H. umbellata do not fare as well as H. paniculata. Some species, like H. quercifolia and H. aspera, prefer shadier spots. Dirr recommends using drip irrigation for plantings of Hydrangea, specifically using drip tubing, extender lines, and emitters attached to a garden hose, possibly with a timer.
The Michael Dirr book says that good soil preparation (not just of the planting hole) ahead of time is the best thing for hydrangeas. He does not subscribe to the rule sometimes put forth, that the hole must be 3 times as wide as the root ball. I also consulted Hydrangeas: A Gardener’s Guide by Toni Lawson-Hall and Brian Rothera (Timber Press, 1995) which says the hole should be 2 times the rootball’s width and depth. Be sure to check the state of your plants’ roots. You want to make sure they are not coiled in a spiral or restricted in any way. You may need to tease out or prune the roots a bit before planting.
Professor Linda Chalker-Scott discusses planting procedures in her book, The Informed Gardener (University of Washington Press, 2008), advising that the planting hole only needs to be the depth of the root system, but twice the width. She also recommends against amending the planting hole in any way. Backfill the hole with native soil, not a soil amendment. The idea is not to ‘spoil’ the plant by putting rich compost just in the hole, which will deter the roots from spreading out into the surrounding area. Here is more of her writing on this subject.
You have already amended the surrounding soil, so the addition of gravel to the hole is not necessary, and is possibly not a good idea, according to general planting information from University of Minnesota Extension. Here is an excerpt: “If soil drainage is inadequate, species that are tolerant of poorly drained soils may be planted, or soil drainage may be improved. This can be done in two ways. If a hard pan is present (a compacted, impermeable layer of soil) with an underlying layer of well-drained soil, a hole can be dug down to the permeable layer to provide drainage for the planting hole. If the soil is poorly drained and there is no well-drained layer below, a tile system can be laid. This, however, is expensive and requires the assistance of a professional for proper design. Simply adding gravel to the bottom of the planting hole will further decrease oxygen availability to the root system.”
of gravel at the bottom of the hole to improve drainage as I suspect that the base soil is mostly clayey.