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Common Plant Questions


I’ve been working in Horticulture for a while now and for the past year I’ve been doing a lot of work with cultural and pest/disease related problems. I am approached with a variety of problems and questions but some questions come up more often than others.
I thought this would be a good way to answer some of them and maybe learn a few more solutions myself. I learned a lot from school, nurseries and greenhouses I’ve worked at but the best info has always been from talking with other gardeners, growers and landscapers.
Keep in mind that I’m in Michigan and a few things I’m mentioning really only apply if you have hard winters (temps here can reach as low as -15 to -20F or -26.2 to -28.8C).
A lot of times people come to me with a problem and assume it is a pest/disease problem but more often than not it is a cultural problem.

1) Inner needles/scales turning brown on conifers.

Conifers shed needles in Autumn, some shed every year and some shed every 4-5 years. It can be worse if the plant is too dry (or wet). Winter is the driest season so an evergreen exposed to wind and sun may also get burned in the winter (inner growth or previous seasons foliage). It’s especially noticeable on conifers with softer foliage. Every year I end up trimming a lot of Chamaecyparis obtusa varieties because they don’t handle winters here very well if they are in an exposed site, especially their first couple of years in the ground. It’s usually worse on the varieties with yellow foliage too.
I usually give conifers roughly the same kind of treatment I give broadleafs before winter. 1) Make sure they’re not dry heading into winter. 2) Make sure the sensitive ones have some protection from wind/sun. 3) Mulch.

2) Hydrangeas not blooming

This is the most common question I get asked and there are several possible solutions. Where I live the first thing to look at is whether or not the variety is hardy. Most H. macrophylla and H. serrata will grow here but their flower buds are not as hardy. The only way to get reliable blooms is to get a variety that flowers on new growth (remontant types such as Endless Summer). It also helps to plant them in a protected area (near the house and protected from winter wind) and to mulch them before winter. Frost can also damage flower buds. Often times we will get a warm up in Spring that forces plants to push soft new growth and then we will get a frost that damages it. Late frosts in Spring and early frosts in Autumn can kill the flower buds. When my hydrangas don’t bloom well, it’s usually not the winter but a hard frost in May. The third reason is pruning, a lot of people cut off the flower buds without realizing it. The best time to prune is immediately after flowering. If you prune them in Spring or Fall you could be removing flower buds. If you prune them in Spring, just remove any branch tips that may have died during winter.
Also make sure that they have enough sunlight and water. They need a lot of water if they are in full sun or the weather is hot. Try to water them before they are wilted. I fertilize my hydrangeas in Spring with Holly-tone but any slow-release fertilizer works great too. Avoid giving them a fertilizer with too much Nitrogen (the first number on the bag) or you’ll end up with more leaves than flowers.

3) Hydrangea blossoms from Pink to Blue

It’s not the soil pH that results in blue flowers but the amount of aluminum the plant can absorb. In order to be able to use the aluminum in the soil it needs to have an acid pH (5.0-5.5). The best way to change the color from pink-blue is by adding Aluminum-sulfate available at any garden center. If the soil is very alkaline, it will be more difficult to change the flowers blue and keep them that way. It’s also important not to add to much aluminum-sulfate because it can kill the plant. Keep in mind that some varieties don’t turn blue and some varieties have different shades and color intensity. Adding fertilizer can also effect coloring, so if you’re trying to turn your flowers blue then avoid applying a fertilizer with too much phosphorus (middle number on fertilizer bag). Phosphorus makes it harder for the plant to absorb aluminum. Try to add aluminum sulfate a few weeks before flowering. I try to add it when the flower buds are visible but still small.

4) Black Knot

I wasn’t going to add this but I get asked about it all the time in Spring. I see it all the time on plums but it can also appear on cherries and maybe peach? It looks like a warty growth on the stems and it’s most noticeable in Spring due to the wet weather. Last year, it started showing up a lot in June here because we got a lot of rain with cool temps. Anyways, I thought I’d mention it now because winter is the best time to get rid of it. Cut off infected branches and bury them, burn them or give them to an unfriendly neighbor. I’ve never dealt with a severe problem but it can cause quite a bit of dieback. Next time I see it, I’ll add a picture.

If anyone has any additional solutions to the problems I listed, please let me know. I didn’t include every possible explanation for each problem but I tried to add the ones I run into the most.

More blog posts by rkwright



Thank you RK this is very helpful, especially the hydrangea information.

8 Jan, 2012


So here it is. Finally :) Thank you!

8 Jan, 2012


Skwright, may I ask for your opinion on how to cut Hydrangeas according to the sort? I mean, I know how to cut H. macrophylla (as less as possible), but what about H. petiolaris, H. quercifolia, H. arborescens, H. panniculata?

8 Jan, 2012


Interesting to read about the Hydrangea flower colour. I was wondering how to do it.

8 Jan, 2012


Interesting blog RK....useful information for those who need it :)

9 Jan, 2012


Thanks, glad the info was useful! As for the pruning of different species: H. paniculata- fall after flowering or winter. flowers on current seasons growth. H. quercifolia- flowers on old wood, prune after flowers are spent. Can prune as late as August. H. arborescens- after flowering or winter. Flowers on new growth. You can cut it back to the ground in winter and get a good display in Summer. Hydrangea vine- do you really want to cut it? Probably best after flowering, flowers on old wood.

9 Jan, 2012


Thank you rkwright. I just checked Endless Summer and found it is American breed. Very practical. I wonder, what colours are available in the US?

9 Jan, 2012


thanks for this, Rkwright. I was especially interested in the confier browning: I've lost three mini-conifers that browned all over, and the one I've still got has a brown patch.

8 Jul, 2012


What kind of conifers were they? The only ones I sometimes get ugly browning on are Chamaecyparis obtusa but don't have many problems once they are established and if they are planted out of the wind. Some conifers naturally turn a little brown in winter but the color returns to normal in Spring. Are you growing them in containers or the open ground?

10 Jul, 2012


Everything's in pots, as I don't have any ground worth speaking of - three tiny beds, with a layer of brick six inches down! besides, I have a back injury, and getting down would be a prob, so I have tables with everything on them, apart from the large ones which can go on the ground.

I don't know what type they are: the labels just said "conifer", very helpful. There's not much wind here, but I thought it might be because they were a bit crowded together. I did ask a question but no one could pin them down exactly.

It doesn't really matter, cheap plants from a supermarket - but in anotehr way it does, if I don't know what I did wrong I'm liable to do it again, or to let it happen again.

10 Jul, 2012


That is why I asked if they were in containers. Are they exposed to a lot of freezing temperatures? Having plants in containers makes them more susceptible to extreme heat or cold. If you use stone or clay pots, they don't hold in heat like plastic does and it lets the plants breathe a little easier.

10 Jul, 2012


I've only got plastic pots, but I'm thinking of insulating them with bubble wrap - I can't lift much, and clay pots are a load even when empty - dounle that for troughs!

Double prob is that I'm using plastic plant tiers to get more on the table - means that cold air can get at them from underneath as well. I need to work out how to block that avenue off.

My garden's pretty sheltered from wind, whether that makes a "cold pocket" I don't know - got snow earlier this year, but then, everyone around got snow as well.

11 Jul, 2012

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