Growing Concerns 571: ''The Rocket', fertilizer with rain, Astilbe

Late Spring!

Do your research to learn what's special about a perennial like 'The Rocket'


Dear Janet,

I'm shopping for perennials and wondering what's the difference between Ligularia przewalskii and Ligularia 'The Rocket'?


Dear L.,

 'The Rocket' is the variety name, a common-language label that follows a plant scientific name. Such a name is given to an individual of a species when a grower finds something in that one plant worth promoting over the parent. Usually that variety is then reproduced by cloning -- dividing or tissue culture -- rather than collecting and growing its seed, since its seedlings may be as different from it as it was from its parent.

Growers name varieties for many reasons such as larger flowers, better color, disease resistance, fast growth or dwarf size. That difference might not be apparent in the name so you must check a perennial encyclopedia or catalogue listing. 'The Rocket,' a hybrid between Ligularia przewalskii and L. stenocephala, was named in the garden where it occurred by English perennial wiz Alan Bloom because it "...brought very favorable comment." His description of the plant in his book "Alan Bloom's Hardy Perennials" forms the basis of most other write-ups. He rates it "superior" and "handsome" but he's not specific in what makes this five foot, dark stemmed shade plant with deeply toothed leaves and yellow spike flowers better than its parents. That Bloom! He's not just a good plantsman who's been growing for over 70 of his 90-plus years, he's a great salesman. He knows that if people say "that's nice," then you give it a unique name and sell it as special!


Dear Janet,

Things seem a little pale in  my garden. I did fertilize in spring. Is it possible that all the rain has washed away the fertilizer?


Dear J.S,

Entirely possible. Water soluble fertilizers, especially powders dissolved in water and sprinkled on, need to be applied a bit at a time throughout the plant's active growth season. Lots of water can rinse even a granular fertilizer right down below the root zone, unless it is something like Once or Osmocote that has been formulated to release slowly over time.

Short reports

Astilbes are finally going to bloom!

So reports M., who has been trying to grow astilbe to brighten a summer shade garden and "...tried everything but every year they turn brown rather than bloom." This year, M. used a new fertilizer and credits it with the pink blush on his earliest blooming astilbes.

Not to burst your bubble, M., but you might credit the late rain, not the fertilizer. Astilbes tolerate a lot of shade and still bloom, but they are entirely intolerant of drought. Most years, three early-June coincidences can conspire to ruin the bloom of astilbe under trees: As the astilbes begin to set flower buds, the spring rains end and the trees finish leafing out. Since a tree in full leaf uses an enormous amount of water and an astilbe in bud will only keep those buds if it stays moist, something usually gives and that's the astilbe. The buds abort.

For the best astilbes, water more. Never underestimate a tree's effect on soil moisture. That means you shouldn't set the sprinkler by the calendar. Turn it on whenever the soil begins to dry out, even if that's every day.

High time to cut the spring bloomers

Want to keep a rhododendron, azalea, lilac, weeping cherry, forsythia or other spring blooming tree or shrub smaller than it wants to be, yet still have a good flower show next spring? Then do your pruning now and quit for the year. The branches of these plants must mature this summer in order to set the flower buds by fall that they'll carry through winter. If you cut after the beginning of July, you may be removing branches that had set themselves up to bloom. Replacements that begin forming after early July may not have time to follow suit.

When you cut now, take off as much height or width as you expect to get in growth for the rest of the summer, so you don't feel the need to prune again. That may be 12 inches for a forsythia or cherry, six for a rhododendron, but it can vary with a plant's age and location. You know how many times you have been pruning that shrub in summer, and how much you cut off each time -- do the math and take that much off in one cut.


Green thumbs up

to gardening all summer. You can sit back after Memorial Day and enjoy the fruits of your spring labors. However, you can plant in June, July and August, too, adding color to existing beds or making a new garden. You can transplant, as well. I have often moved summer bloomers, in bloom. The keys are watering first, digging big and watering attentively afterward.


Green thumbs down

to putting the squeeze on as you plant. If the root ball is a bit too tall for the hole you dig you may be tempted to press down to force a fit. Resist the urge! The peat-bark mix in most potted perennials, annuals, shrubs and trees will eventually return to its original size, rising out of ground to expose the crown and upper roots to drought, decline and even death.

 Originally published 6/19/04