Blue sea holly (Eryngium) is suitable for growing in U.S. Department of Agriculture Plant Hardiness Zones 5 through 8. It has stiff, spiny blue-green leaves and grows to 36 inches high and 24 inches wide. It produces outstanding blue, cone-like flowers in midsummer that are borne on the top of long stems suitable for cutting. These long-lasting cut flowers add interest to fresh flower arrangements; they can also be dried. Drying them in a dark location helps preserve the outstanding blue colour.
- Skill level:
- Moderately Easy
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Things you need
- Granulated organic fertiliser
Clear the planting area of weeds or other vegetation and pulverise the soil to a depth of 8 inches.
Spread a 2-inch layer of well-rotted compost over the planting area along with the amount of granulated organic fertiliser recommended for new flower beds on the fertiliser label. Mix the fertiliser and compost into the top 6 inches of soil. Level the soil with a rake or hoe.
Water the sea holly while it is in the planting container by soaking the soil until water runs from the bottom. Do this one hour before removing the plant from the container.
Remove the blue sea holly plant from its container very carefully. Do not disturb the taproot that is growing straight down from the bottom of the plant.
Dig a hole deep enough to accommodate the entire root section. Do not crimp or bend the taproot in any way. The blue sea holly plant should be planted at the same depth as it was planted in the container. Gently place the improved soil around the root system of the plant and lightly tamp down the soil around the root system.
Water the soil around the plant to allow the soil to settle around the roots of the plant.
Add a 1 inch layer of mulch around the plant to conserve moisture and prevent weed competition.
Water the blue sea holly plant when the top 2 inches of soil in the planting area is dry. Blue sea holly is a relatively carefree plant and will decline if the soil is overwatered.
Tips and warnings
- Find a place to plant sea holly plants that is well-drained and receives more than six hours of direct sunlight each day. This is considered a full-sun location. Blue sea holly becomes leggy and produces soft foliage if planted in the shade, which makes it susceptible to insect damage and fungal disease.
- Purchase sea holly plants when they are small, 3 to 4 inches in height or smaller. Taller plants have developed a long taproot that easily is damaged by transplanting.
- Do not use chemical or fast-acting water soluble fertilisers on the soil around the blue sea holly plant. Excess fertiliser applications causes the leaves to have brown margins and prevents blooms from forming.
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