One of my favorite summer flowering perennials is the globe thistle. The flowers are steel-blue, a color rare to find in the garden during the summer. The globe thistle flower is in the shape of a blue ball one to two inches across and covered with hard-pointed flower buds silvery-green in color that open to reveal a deep blue flower. The flower is bristly--you would be wise to wear gloves to pick it for an arrangement for the kitchen table. As a cut flower, it will last for several weeks and in the garden for a month or two.
The foliage looks like a dandelion growing in a rosette around a central stem. The leaf is silvery-green, deeply cut with many indentations that are pointed. Some of these points are very sharp, so you will not have to worry that the kids next door will steal the flower from your garden for their mother.
The plant will grow 2 to 3 feet tall and produces many side branches that contain 3 to 5 flowers on each stem. When the flower go by, remove them and new stems will develop on the plant with more flowers. Globe thistles will bloom for several weeks, especially if the weather is hot and dry.
The plants almost look like weeds growing in your garden at first and like most of the plants growing wild on the side of the road. Once you plant it in the garden, it will not be mistaken as weed again, because of the unique foliage. The plants are tough and requires little care once established in your garden. They also require little to no fertilizer in your garden--if you feed too often, the plant will grow tall and flop over easily.
Feed them in the spring with compost and keep liquid fertilizer away from them. Plants are drought tolerant and the thick stems will hold the flower up without staking, even in seaside gardens exposed to wind and weather.
Plant globe thistles in a garden with plenty of sun, in a soil that is well-drained and not too fertile. Clay-type soil will rot the root system, especially in the springtime or during the winter.
The root of the plant is a taproot that will grow well over a foot deep and because of this, they do not transplant easily. It is best not to try to divide or move them; if you like them, buy a new plant from your garden center.
Potted plants can be planted in your garden at any time of the year but you must water weekly until the plants have established their permanent roots. Try to keep the foliage of the plant dry when you water, as fungus disease can be a problem during a hot and humid summer.
Keep plants away from flowerbeds that have sprinkler systems installed in them, because globe thistle really likes a dry soil to grow.
If you have a flower bed that is in full sun, hot, dry and nothing seems to grow there, than the globe thistle will thrive there. In rock gardens, near stone walls or groupings of large stones, this plant will do very well as it will tolerate the heat that the stone brings into the soil.
The globe thistle is unique and you will always remember this plant for blue flowers that form during the heat of summer. Butterflies love the flowers when they first open. In the fall, small birds like finches and chickadees will go crazy for the seed in the flower head.
You can cut the flowers when they are in full bloom and hang them from the rafters in your garage to dry. As a dried cut flower, they are wonderful and so is the foliage on the stem, as it also dries well--so do not remove the foliage when drying the plant.