Growing Concerns 42: Great impatiens, stop apples fruiting, sweet corn


Topics in this issue: Impatiens, apples, and corn.

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Cold's a crippler for impatiens, other annuals

I have a bed of impatiens on the north side of my house. Each year they seem to become diseased, rot and die. Could you tell me what's wrong? E.R., Detroit

Someone who grows lots of impatiens, as well as other annuals and perennials, is George Papadelis at Telly's Greenhouse in Troy. I asked him for his views.

"Putting tender annuals like impatiens out when it's too cold, or watering them too much, can lead to rot. Soil is cold on the north side of a house, so wait an extra week or so for it to warm up. See my annuals there, outside? With very few exceptions, all I have out there are the ones that aren't going to be affected by the cold. I'm growing impatiens, too, but they're still inside the greenhouse for at least another week."

"Plants also need to be hardened off, if you buy them from within a greenhouse Hardening off is gradually acclimating them to wind, sun and outdoor temperature. Set them outdoors in a shaded, wind-protected area for a day, then bring them into a frost-protected place at night. Do this for another day and a night, and then plant them out on the third day into a moist bed. This prevents stress and transplant shock that can lead to later disease, stunting, and leaf scorch. Plants that have been held outdoors don't need to be hardened off, but not every garden center has their stock outside quite yet."

Another thought: when your impatiens rotted, did you replace them right away with more impatiens? If so, that was a set-up for repeat infection. Fungus spores would have been waiting there to infect the next batch of impatiens, entering through any breaks in the stems or leaves.

(And a final thought added years later: We all know now about impatiens downy mildew moving into our region in 2012. That was the killing year, when the disease became so widespread all the major growers agreed, 'no more growing impatiens!' However, it's likely that the disease got its foothold here and there before that year and may have accounted for some losses such as this one.)

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Annual flowers should be rotated, just as vegetable crops are, to prevent a cycle of disease/insect build up and reinfestation. Switch to begonias or annual periwinkle (Catharanthus roseus) every few years to break the cycle. Or ask at the garden center for other suggestions - I overheard the staff at Telly's answering questions like this, and they not only had good ideas, they actually seemed to enjoy sharing them.


Stop the apple tree from fruiting?

I have an apple tree in the back yard. The tree is large and very nice but I find it very dificult to pick up apples and keep the yard clean. Is there something I can do so it won't bear apples? R.S., Oak Park

There is something, though it may not be practical for everyone. Apple growers thin the fruit on trees, to get fewer but larger apples. They use a thinning agent (a simulated hormone, also called a growth regulator) to do this. Applied properly, this can cause almost all the fruit to drop off.

Marv Wiegand and Dennis Wegner at Ray Wiegand's Nursery in Macomb have used this, on crabapples. (Crabapples and apples are the same species, distinguished only by the size of the fruit, so this advice applies to both.) Wiegand's produces top-notch plants, so I'm confident that anything they do would also be safe on our prized ornamentals.

Marv explained, "Normally, we don't want to prevent our crabapples from fruiting. We select varieties in part for their fruit, which can be beautiful through the winter. But last year we had quite a number of small crabapples heeled in up at our farm that we didn't want to bear fruit. We wanted them to divert that energy for leaf growth, instead."

Dennis gave me the details. "We sprayed them with a thinning agent when about 90% of the flower petals had fallen off - the label of the product told us how much and when to spray. On all but one variety of crabapple, about 90% of the fruit fell off."

Marv added these qualifiers. "For us, it worked. There are considerations a homeowner would want to keep in mind, though. Spraying a full sized tree may take special equipment, expensive. Also, what we used is probably not available in quantities suitable for a homeowner - we made 100 gallons of spray mixture from each package. It's also been hard to get hold of this year, maybe because regulations regarding its use are changing. And you can't overlook the fact that improperly used, it can also harm bees, which is not good: bees are essential to agriculture and their populations are already way down recently because of mite infestations."

The product Wiegand's used is based on napthaleneacetimide, which is also the basis of a product called Florel. Florel is currently registered for use on apples to promote flower and reduce fruiting. Write for further information about Florel to the manufacturer, Monterey Chemical Co., P.O. Box 5317, Fresno, CA 93755.

Maybe it would be simpler to do what I do with my apples? I'm not particularly interested in harvesting my apples, so I don't have to tend to cleanliness for the sake of disease and insect control. I put a large bed of groundcover under the tree, let the apples fall into it and decompose there. It may not be for everyone, but it works fine here.


  Why sweet corn doesn't mix well with others

Perhaps you can clear up a confusion for me. Is it all right to plant different varieties of sweet corn together? I'm referring to the "normal sugary" or "sugary enhanced" varieties. I understand that supersweet requires isolation. I have heard that cross-pollination can ruin both varieties if planted together yet I've also seen the suggestion to plant varieties with different maturities, which seems contrary. I have a small garden and the most I could separate two types is by ten feet or so. D.H., Chelsea

Yes, you can mix and match sweet corns (sweet, sugar or sugary enhanced), but keep the supersweets away from both sweet and sugary enhanced types.

Most of us choose our corn variety from among three basic groups: normal sweet corn (also called sugar corn - 'Silver Queen' is one); sugary enhanced varieties ('Sugar Buns' just begs to be included in my garden); and supersweet types (such as 'Northern Xtra-Sweet'). What sets each group apart from the others are genes. Sweet/sugar corn is unique for its "su" sugar gene, sugary enhanced has an "se" gene, and super sweet has an "sh" gene. Good catalogs list each group separately.

Corn with an su or se gene can grow near other corn with su or se genes without problems. But if sweet or sugary enhanced corn is pollinated by a plant that has an sh (supersweet) gene or vice versa, the offspring - the kernels on the cob - may well be starchy rather than sugary. So supersweet corn types have to be grown separately from sweet and sugary enhanced corns.

Within the supersweet group, or within the combined sweet-sugar enhanced group, you can mix several varieties without problem. That's where the different maturities come in. This mixed group of sweet and sugar enhanced types would be fine together: 'Quickie' sugar corn with an se (sugary enhanced) gene ripens in 65 days; it can be grown with 'Tuxedo' which also has an se gene but takes 79 days to ripen; round out the season with 'Silver Queen' with an su gene and 91 days to ripen. This combination of supersweets would give you fresh corn over several weeks: 'Northern X-tra Sweet' (71 days to maturity); 'Starstruck' (78 days); 'Hudson' (86 days).

To grow supersweet corn and sweet, or supersweet and sugar enhanced, you would have to plant the groups at least 400 yards apart or plant one group 4 weeks before or after the other, to prevent cross-pollination. Certainly you can't do this - but doesn't it also make you wonder what types of corn your neighbors are planting?

I don't know anyone who can keep up with all the subtle differences in vegetable and flower types without a current reference. No matter how many you've grown, another variety or another whole group is introduced every year! I turned to my Johnny's Selected Seeds catalog for help in this - it's a great resource for gardening information as well as excellent seeds. Write for a catalog to Johnny's Selected Seeds, Foss Hill Road, Albion, Maine 04910-9731 or call (207) 437-4301.

Originally published 5/7/94