Growing Concerns 508: Crocosmia seeds, PJM Rhododendrons

Early Spring!

This past winter seemed hard to people but it was ho-hum for plants


Dear Janet,

I grow Crocosmia, having very good luck with them although I learned recently that they aren't normally hardy here. I do wonder if this very cold winter is going to be the death of them? Actually I'm kind of worried about quite a few of my perennials, after such a long cold winter. Guess you can only wait and see on something like that.

I've collected Crocosmia seeds, strewn them on the ground, and tried to get them to germinate indoors, but always without success. Do they require stratification to germinate?


Dear D.,

I'm not worried for the majority of perennials. We were colder this winter than in the recent past but still within the norm for USDA hardiness zone 5 -- meaning our minimum winter temperature stayed above -20 degrees F. So any plant hardy to zone 5 that was healthy going into fall should be fine now.

The ones to cross your fingers for are plants hampered by debilitating factors such as poor drainage or drought stress, or species like Crocosmia and dusty miller that were overwintering here recently because our winters have been more like the warmer zone 6.

Crocosmia is marginally hardy in zone 5 so it's at risk even in a normal winter. Don't lose sleep over it, but don't waste time either. If it doesn't show growth by mid- to late April, buy more.

Crocosmia seed doesn't need a cold period before it sprouts. It germinates in just 14 to 28 days, at about 70F. However, seedlings are more tender than established plants. If you sow the seed as it ripens in fall it will sprout during November's Indian summer and the seedlings will die during winter. So collect the seed in fall, store it inside and sow it in spring. After a season's growth the plants are more likely to survive winter.


Dear Janet,

In summer of 2002 we planted three PJM Rhododendrons. These were planted in July when our home was professionally landscaped. At planting time we were told not to fertilize during 2002. We have clay soil beneath a layer of top soil and we are careful not to overwater. The question is: when should we fertilize and what is recommended. I know they require an acid soil and we do have Miracid on hand. Do we use only this or is there a better product? Also how often should we apply?

Final question: When is best time to prune, if at all during this coming season?


Dear K.B.,

Minerals essential to vigorous rhodo growth don't dissolve when the pH is so high as it is in Michigan, above 7.0. What won't dissolve, the plant can't absorb. So rhodos and azaleas wither away. This may not be apparent to you but it is very clear to the practiced eye. I regard most such shrubs here as examples that could be featured in the horticultural equivalent of an ad asking for donations to feed starving children.

For that reason, the rule about not fertilizing during a woody plant's first season can be disregarded for rhodos and azaleas -- they will not root out readily into the native soil, so will always rely on supplements. Once a month, April through July, use Miracid or another water-soluble formula for acid-loving plants. Better yet, apply it weekly at quarter-strength, sprinkling it onto the leaves as well as the soil. Also spread an acidic mulch or slow-release fertilizer under each plant every year. The mulch might be an inch of cocoa hulls or coffee grounds. The fertilizer could be a quarter-cup of Osmocote or dusting of cottonseed meal under the mulch.

The best time to prune spring blooming shrubs such as these is right after they bloom. Start pruning once they reach the size you want them to be, shearing them back by the same number of inches they have shown they are likely to grow each year in your garden. After shearing, cut every fourth or fifth branch back a few inches further, to keep new growth coming from well within the sheared outline.


Short reports:

The sap's up!

You can still prune the "bleeder" species such as maple, beech, birch and grape but be prepared for the flow. It doesn't harm the plant but does affect the soft-hearted gardener, and can gunk up your clippers or saw.

Launder your gloves or buy new, regularly.

It's worth the price to keep your hands healthy. Plain cotton gloves are probably best to avoid the all-too-common fungus infections under the nail. If you use rubber gloves against the dampness of spring, wear thin liner gloves under them to keep moisture from building up in the finger tips.


Green thumbs up

to my first glimpse this year of a foraging groundhog. Much as I dislike your irreverent snacking and prodigious digging in my gardens, Mr. G, it is thrilling to know that our seasonal interplay is about to resume!


Green thumbs down

to walking where it's wet or the snow melted last. The air may be 70 degrees but the soil a few inches down is still frozen. Let it thaw and drain a few more days, or you'll pulverize the soil between foot and ice.

Originally published 3/22/03