The care information provided in this section represents the kind of practical advice is available for all the plants in this web site if you subscribe to the monthly customized newsletter Yardener’s Advisor.
Spireas don't usually need watering except when they're first planted, in time of drought, or in late fall before the ground freezes for the winter. If you do water, give your plants about 1 gallon of water twice a week or run your drip irrigation system or sprinkler for 20 minutes twice a week. If you have clay soil which absorbs water slowly, deliver the water in 2 sessions, a few hours apart. Older shrubs need watering only during severe drought. Keep spireas well mulched.
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Spireas are not heavy feeders, so, after they have been in place for a season, start to fertilize them once every year in the fall after their leaves fall or early spring, which is better in the South. Sprinkle some all-purpose slow-acting granular fertilizer on the soil over their roots for the rain to soak in. This will provide consistent, steady nutrition for several months over the growing season.
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Spireas do best when they have a 2- to 4-inch layer of organic mulch on the soil over their root zone all season long. Keep the mulch about 6 inches away from the stems to avoid stem decay and rodent damage. Mulch with chopped leaves, pine needles or wood chips. Avoid unchopped leaves because they mat together, preventing water from getting into the soil.
Organic mulches contribute valuable organic matter to the soil over plant roots as they decompose. Mulches also cool the soil in summer, and reduce water run-off and evaporation. They prevent soil from splashing up onto the lower leaves, reducing chances of disease from fungal spores. Use mulch year round to deter weeds, too. Those that develop are easy to pull. If you don't mulch, hand-pull weeds growing close to the shrub to avoid damaging its root system.
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Pruning or Grooming
Prune spireas once a year if you feel that you need to maintain their shape or reinvigorate older shrubs. For pruning purposes spireas divide into two groups: Prune those that bloom on the last year’s wood such as Thunberg and van Houttei just after they flower, so they can grow new wood right away to produce next year’s flowers. Prune those spireas whose flowers typically appear on this current year’s newly grown stems early in the spring before this growth starts. Observe your shrub’s flowers closely to see which kind of wood they bloom on, if you don't know the particular kind of spirea you have.
Now and then thin out old thick spireas clumps with hand pruners or loppers by removing old canes from the base. As the plants mature and flowering declines, cut the plants back by as much as 30% to stimulate newer, more productive growth from the base of the plant. Many of the newer, compact hybrids can be cut right back to 4 to 6 inch stems to renew them.
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