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Mulch and Outdoor Bulbs
About Mulch and Mulching
Mulch protects your bulb plantings. It regulates soil temperatures, retains moisture, and hinders weeds from growing in your beds.
When bulbs overwinter in your garden, apply mulch heavily in autumn. Mulch insulates the soil and naturally releases nutrients as it decays to fertilize your plantings. Mulch also helps to protect the soil from freeze-thaw cycles that sometimes can uproot bulbs.
Mulch has a neat appearance. It keeps cultivated soil from crusting, helping it absorb water without runoff.
Many bulbs, including those that are shallowly planted, take soil temperature fluctuations in stride. Outright freezing and thawing cycles, though, may kill bulbs, dislodge them from the soil, or break their developing roots.
Choosing Mulch
When selecting mulch, opt for organics rather than rock, plastic, or sand.
Mulches made of plant matter decompose and feed your plants. When organic mulch breaks down, soil bacteria first absorb nitrogen and oxygen. Low nitrogen robs shallow-rooted weed seeds, blocking them from growing. This rarely affects deeply rooted bulbs.
Later, organic mulch releases its own nutrients, feeding both your bulbs and helpful soil organisms that keep soils loose and workable. Mulch, therefore, is a partner to your bulbs.
Good mulch choices include shredded bark and leaves, wood chips, organic compost, ground cocoa and rice hulls, and weed-free straw.
Avoid using sphagnum moss or peat as a mulch for bulbs. They allow water to run off. More importantly, they are mined from rare natural bogs and are unsustainable.
Natural bogs also are important wildlife and bird habitats. They are threatened by both depletion and over-harvesting.
Mulch as Insulation
The second way mulches help your bulbs is by protecting them from sudden changes of temperature.
Soil is a good insulator—temperatures at shallow depths frequently remain constant unless a cold snap follows chilling rain. Water chills quickly. Because most bulbs lie deep in the soil, they are protected from sudden frosts.
Mulch adds even more insulation, added protection.
Applying Mulch
Apply mulch in a layer, 1–2 in. (25–50 mm) thick.
Sprouting bulbs will push through the mulch as they grow.
For summer bulbs such as gladiolus and lily, rake the mulch away from their stems once foliage emerges. Clearing prevents too-moist conditions or harboring fungal spores that cause stem diseases.
A cleared circle, 2 in. (50 mm) in diameter, usually is sufficient to protect summer bulbs.
Step-by-Step Instructions
Mulching Around Bulbs
Apply mulch after planting but before bulb sprouts appear. Mulch performs many useful tasks for your bulbs and dresses your landscape.
Use organic mulches—wood chips, fine ground bark, compost, salt hay, or cocoa hulls—for best results.
Use a garden cart to carry the mulch, together with a mulching rake, to the site, then follow these steps:
How to Apply Mulch Over Bulbs
Begin by dumping cartloads of mulch at several points within the bulb planting bed. The contents of a full 5-cu. ft. (0.15-sq. m.) cart or barrow will cover a 15–20-sq. ft. (1.4–1.9-sq. m) area.
Spread the mulch over the bed’s surface with a long-tined mulching rake. Make an even layer, 3–4 in. (75–100 mm) deep. The mulch will settle to a layer 2–3 in. (50–75 mm) deep.
For planting beds with trees, shrubs, or perennial plants in humid climates, rake back the mulch to clear soil, making a circle 4–6 in. (10–15 cm) wide away from each plant’s trunk or stem.