How to Change the Color of a Hydrangea and the Best Soil to Use
Botanical Names: oakleaf hydrangea (Hydrangea quercifolia), panicle hydrangea (Hydrangeapaniculata), smooth hydrangea (Hydrangea arborescens), French hydrangea (Hydrangeamacrophylla), lacecap hydrangea (Hydrangea macrophylla normalis)
Choose the right soil for hydrangeas, and your plants will bring color to the landscape for years to come. Choose the wrong soil, and your landscaping with hydrangeas will be short-lived. Hydrangeas aren’t especially picky about soil. Like most plants, they tend to grow best in soils that drain well. Heavy clay soils that retain water can quickly kill hydrangeas.
Instead, aim to give hydrangeas soil that’s fertile and well-drained. In other words, water should pass through the soil fairly easily so that it provides moisture to the root zone of hydrangea shrubs but doesn’t sit there to trap roots in a puddle. Poorly drained soil holds water, sometimes allowing it to puddle on the surface. Typically poorly draining soils have a high clay content. These soils can quickly rot hydrangea roots.
Of all the hydrangea shrubs, oakleaf hydrangea (Hydrangea quercifolia) tolerates the most moisture. With these hydrangeas, soil can tend toward a heavier type but still needs to drain well, or the oakleaf hydrangeas will succumb to root rot. With panicle hydrangea (Hydrangea paniculata) or smooth hydrangea (Hydrangea arborescens), soil can also tend toward the moist side, as long as it drains well. But panicle hydrangea soil can also be droughty. This hydrangea tolerates dry soil better than the others.
Soil for hydrangeas of the French (Hydrangea macrophylla) or lacecap types (Hydrangeamacrophylla normalis) needs to serve up a higher moisture content. These hydrangeas both have big, flat leaves that require a lot of moisture to maintain. When you’re preparing planting areas for Hydrangea macrophylla types, aim to create soil that’s fertile and well-drained.
Work plenty of organic matter into soil. Soils with a higher clay content need more organic matter than those that already have a well-draining structure. You can use a variety of organic materials to amend soil for hydrangeas. Homegrown compost, bagged compost and composted manure are all great choices. You may also find excellent regional sources of organic matter, such as cotton hulls, ground fir bark or dried seaweed. Work with whatever is available to you atthe most reasonable cost.
By adjusting the pH of soil for hydrangea macrophylla types, you can shift flower color. The soil pH affects how much aluminum plant roots can extract from soil. In acid (low pH) soils, aluminum is readily taken up by roots, resulting in bluer flowers. In alkaline (high pH) soils, aluminum is tied up in the soil, resulting in pink blooms.
To shift hydrangea flower color, focus on fertilizer. Add lime to soil to raise the pH and make pink blooms. Add aluminum sulfate to soil to shift flowers toward blue and purple hues. When should you add lime or aluminum to soil? Start your soil amending process in late fall or earlyspring. Continue adding dolomitic lime to soil several times throughout the growing season.With the aluminum sulfate, carefully follow package directions to avoid burning roots.