May 29, 2003

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: I have been told by a friend that if you cut flowers from lilacs that you will never get a flower on that branch again. I started a purple lilac from a big bush about four years ago and this is the first year it flowered. There are clusters of two or three on three different branches. Will it hurt the bush if I cut them? Will it flower again? How far down should I prune in the fall? (E-mail reference)

A: It will not hurt the lilac to cut the flowers and shame on the person that told you that. The only way a lilac will be kept from flowering, assuming all else is equal, is to cut the plant back in late July or August. The flower buds have already formed for next year's show by that time.

Q: Last year I planted numerous blue spruce throughout the yard on my farm. All of those planted in the existing tree rows and other rather shady areas thrived but those planted in direct sunlight died even though I watered them weekly. The needles turned brown and dried out by mid summer. I am planning on planting again in the same locations. Should I plant something to shelter them from the sun and/or wind? (McClusky, N.D.)

A: Probably wouldn't be a bad idea, although I am surprised at what you told me. They are usually as tough as steel girders at the young stage.

Q: We bought a house that had a nice landscape design but everything was badly overgrown. The Korean lilac was enormous so my husband sheared it back several times but did not go deep inside and thin it. Now it is a very dense ball with branched ends but empty inside. It is still too big for its space. I have been trying to thin it from the inside but that makes holes in the plant. Can we cut it back to remove all the leaves and new shoots for a few years or would that kill it? Is there a way to make it significantly smaller with all those bare branches inside? (E-mail reference)

A: Your question comes too late for this year so keep this answer in mind for earlier next spring. Cut it down as close as you can to the soil line before new growth begins next spring. It will send up a flush of new growth that you can then shape and thin to your heart's content. If that seems too drastic, then remove about a third of the canes, down to the base, each year for the next three years and new growth will emerge as in the first suggestion.

Q: We want to replace four 40-foot evergreens which we removed because of age and disease. I am looking for an arborvitae which will have full sun exposure, grow to a height of 25 to 40 feet and fill out to a 6 to 10 foot width. It must retain greenish color in winter months, offer good highway screening and noise reduction and be winter and most bugs resistant. I have found types of hetz wintergreen arborvitae, white pine (pinus strobus), and nigra as possibilities. (Valley City, N.D.)

A: Any one of the three would do but since you asked I'll give you my highly biased opinion. Plant the pinus strobus 'Fastigiata' if you can find it. They are beautiful under-planted trees with long graceful needles, five to a bundle. All three will need spraying with an anti-desiccant to get them through the winters, doing so in mid to late October. Be brave! Be different! Try to get some plant diversity into our region. The species is hardy to zone 3 so with proper care they can make it. They are narrower than they are wide and I don't know how tall they will get in N.D. My second choice would be the nigra arborvitae.

Q: I have a two-year-old jade plant. It was repotted last summer and had been doing really well until recently. I don't know if it is getting too much water or not enough. I also don’t know if it’s getting enough sunlight or if possibly something else is wrong. The branches turn green and then fall off. It happens only on the side that does not get much sun. Are the branches supposed to turn green? Please help me save this plant! (E-mail reference)

A: No, the branches are not supposed to turn green. Generally branch and leaf fall indicate an insufficient environment to support the plant. It may be too much water, inconsistent watering patterns, too much light at one time and not enough at another. Basically the jade needs some constant temperatures above 55 degrees, plenty of bright light with some direct sunlight, water when needed, which is when two-thirds of the potting soil is dry, then giving them a complete soaking. You need to fertilize every two weeks during active growing periods and repot in the appropriate soil mixture every two to three years. If they get too big to repot, then simply topdress the pot with fresh potting soil.

Q: I love the looks of the small leaf linden and I hear they are a very hardy tree. Toward fall of last year I planted one in my front yard. I made the hole larger and filled it with gravel, sand and soil to help with drainage. Then we received tons of rain. I noticed the tree start to lose its leaves early as if it were going dormant for the winter. Will the tree survive? So far this spring it hasn't produced any leaves but the tree still looks like it’s alive. The branches are very flexible and it has buds but I’m not sure if they have swelled much yet. (Twin Cities, Minn.)

A: The person that told you what to do when you planted gave you some poor advice. It may be too late to reset the tree. If you can, don’t use gravel or sand because it’s not needed. If the tree has already leafed out, then let it go for the season and watch the water requirements. Replant it when dormant, either this fall or early next spring.

Q: We moved into a house that has two mature evergreens in the backyard. We trimmed the branches up about three to four feet. After we clean up the immense pile of needles underneath, is there anything that will now grow as a ground cover? We'd prefer that rather than decorative rock or bark. (Aberdeen, S.D.)

A: Yes, it’s done all the time. Simply rake up the needles, scratch up an inch or two of the soil, bring in some good topsoil and plant to your heart's content. Plant material is more interesting to look at than rock mulch.

Q: We have some very small spruce trees. They are approximately one and a half to three feet tall. What should we do as far as trimming to help optimize growth and shape? (E-mail reference)

A: Very little with trees that small and young. They generally retain a decent shape throughout development. Simply prune back anything that is distracting from the uniformity desired. Always cut back to where needles exist on the branches. Never cut back to a bare branch. Christmas tree growers will take pines, firs and some spruce and cut them right after new growth has emerged to thicken them up. That's good for growing Christmas trees but not for landscape trees.

Q: Two years ago we dug up lots of raspberry plants from our neighbor and our old patch. We put them in a new bed we created after tilling in some manure. So last year I was expecting to get some raspberries but alas, the canes died. But they were coming from the bottom so I thought we’d be patient until the following year. This year they appear to have again died. These are plants that my neighbor and I have had for years. They’ve always been hardy and have borne well for us. The old bed was getting less productive so I thought it was time to start a new bed. My neighbor came over to look and said our canes look blacker than hers. Hers are leafing out as are the ones in our old bed. Do you have any thoughts on why they would be dying? Also, should I leave them alone for another year or should I just till them up and forget it? We love raspberries and make several things like jam, wine and vinegar. It’s disappointing to have a continuing failure like we’ve had especially with a plant that is rumored to grow like a weed! (E-mail reference)

A: Most likely the problem is the manure you brought in. You can try waiting another year to see if the plants outgrow the root fungus or begin anew somewhere else, sans the manure. I am with you on raspberries! Fresh, frozen, in pies or over ice cream, they are great and good for you.

Q: I sometimes see references to using Roundup by painting it on the leaves of unwanted plants. Can 2,4-D be used the same way if care is taken to have it not contact desirable plants? I’m assuming a jug I have of concentrated weed killer is 2,4-D. It has three different variations of Dimethylmine salt of 2, 4-Dichlorophenox. The instructions say not to use the product for controlling weeds in flower or vegetable beds, around shrubs or ornamental plants. But I would assume that is a reference to application by general spraying of an area. I'm looking for something that may be more successful than Roundup in my fight against ladybells. Their root system is really something. I won't consider Trimec. (Bismarck, N.D.)

A: I have never tried it but can’t see a reason why it wouldn't work. Use rubber gloves and a throw-away paint brush. Good luck!

Q: My daughter recently bought me a spider plant for Mother's day. When does the plant need to be repotted ? This plant has so many babies hanging from it, is quite beautiful and heavy. I have it hanging between two windows and hope it does ok. I love this plant and don't want to kill it. (E-mail reference)

A: You can let it stay as is for the summer. Fall is usually a good time to repot most houseplants, roughly in mid September. Don't worry about it repotting because the plant does well even if it’s pot-bound. I usually just cut some of the roots back, add fresh soil and replace it in the same pot.

Do you have a gardening or houseplant question? Write to Hortiscope, Box 5051, NDSU Extension Service, Fargo, ND 58105 or e-mail to Ron Smith at ronsmith@ndsuext.nodak.edu. Note to e-mail correspondents: please identify your location (city and state) for most accurate recommendations.

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Source: Ron Smith, (701) 231-8161, ronsmith@ndsuext.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu