Sunday, July 30, 2017

The Year of the Mimosa Weed

Although weeds plague our lawn and garden every year, it seems that each year a particular weed takes center stage. One year it was wild violets. The next year it was purslane. A few years ago, we had elm seedlings sprouting everywhere. This year the villain in our yard is a plant we call mimosa weed (Phyllanthus urinaria) because its foliage looks similar to the familiar mimosa tree.

This is a nasty fellow. It invades lawns and flower beds indiscriminately and it is sneaky. It germinates later than most weeds, so late that our spring application of pre-emergent herbicide was not effective to prevent it in our lawn. It also develops seeds as a very small plant and they hide on the undersides of the leaves. So while you are thinking you have time to weed before that critical reseeding time, it is already developing seeds. It has a strong stem and large taproot, so it is not so easy to pull up. Roundup is effective on it but I try to avoid using Roundup when I can, both because it can cause damage to nearby plants and because I'm not convinced that it is not a dangerous chemical (even though there is no scientific evidence to support this idea).

Jack and I have put in a lot of hours pulling up mimosa weed this summer, and I'm determined to get ahead of it next year. Our main problem spots this year were a bed that was not well-mulched and areas of the lawn where the grass was thin. We've been working to get the lawn in better shape this summer because dense, healthy turf is the best deterrent for all weeds in the lawn. Also, next year, we may change our pre-emergent for the lawn to one that is more effective in controlling this particular weed.

If your garden has been plagued by this particular weed, you might find this factsheet useful for more suggestions about how to control it, including a complete discussion of the various chemical controls available.

Wonder which weed I'll be complaining about next year . . . . 

Saturday, July 1, 2017

Repotting my Orchid

Several weeks ago I wrote about how my mother's orchid was nearing the end of its bloom and I was considering whether I should repot it. The first bloom spike had already turned brown and was ready to be cut off, but it appeared that new buds might be developing on the second bloom shoot.  I was undecided about whether I should allow the last few blooms to develop or cut the shoot back to allow the plant to regain its strength. As it turned out, the second shoot simply lacked the energy to continue, and it, too, turned brown. In the end, there was no decision to be made. I cut off both bloom spikes as close to the plant stem as possible and proceeded with the repotting.

When I bought this orchid, it was potted in this clear plastic pot, which was then placed in a decorative outer ceramic container. I always removed the clear container to water the plant and allowed the water to drain out before returning it to the ceramic container. As I mentioned in my previous post, most orchids that don't survive suffer from overwatering. With most houseplants, it's easy to stick your finger in the soil to determine if water is needed but that's not so easy with a bark planting media. I like these lightweight plastic containers because after you've watered a few times, it's easy to judge whether the plant needs water by the weight of the container. Fully moistened bark makes for a lot heavier container than one that has dried out. The other good thing about this type of container is that it allows you to inspect the roots from time to time. Mushy roots are another sign of overwatering.

When I slipped the roots out of the pot, I was pleased to see that the roots, for the most part, looked healthy. I gently teased the bark away from the roots, being careful not to break the roots, which can be quite fragile. Any roots that looked completely dead, I cut off. Be careful with this process because some roots appear to be dead at the top but have a healthy lower part. Notice the white root that begins on the right side of plant and curves down toward the left side. It looks dead near the top of the plant and is split and lifeless looking  as you trace it downward. But the section below the split is very healthy. So be sure to inspect the full length of a root before deciding it is dead. Sometimes, just the tip will be alive.

Here's what the plant looked like after I removed the remaining potting media and trimmed roots that I was sure were totally dead. The roots on the outside of the plant were the healthiest. They were plump and green or white. There were fewer roots toward the center of the plant and they did not look as healthy. They did not seem totally dead, but they were tan and not as plump as the outer roots.

The picture below helps explain the reason why these interior roots were on their way to rotting. It shows the potting media that came out of the plastic pot after I dislodged the media from the roots. It's hard to believe that all this came out of that small pot. The smaller pile on the left is the bark, and the larger pile on the right is spaghnum moss. Because all I could see in the pot was bark, I assumed, incorrectly, that the planting media was totally bark. But it turned out that the bark was on the top and sides, and the center of the plant was tightly packed moss, which tends to stay moist for a very long time. I think this explains the less healthy interior roots, which had too much moisture and not enough oxygen.

I checked with the American Orchid Society (AOS) website before deciding which planting media to use for repotting. The AOS site said:
A fresh, fast-draining, but water-retentive medium is essential to the healthy root system necessary for good growth. Whether a bark-based mix (which drains well, is forgiving of watering errors but breaks down rather quickly), a peat-based mix (which retains moisture well but requires more careful watering and frequent re-potting) or some inorganic, basically hydroponic method, orchids have been grown successfully in a variety of media.

When I went to shop for potting media at my local store, my choices were reduced to bark and moss, and I choose bark. Given that the interior roots seemed to need more air and less water, I repotted using bark totally, rather than a combination of bark and moss.  Making this change will mean that I will have to be careful not to underwater. The bark/moss mix in the original pot was a little more forgiving of somewhat infrequent watering.

I also repotted directly in a pot made especially for orchids, one that has holes in the sides of the pot to improve air circulation. Since this type of orchid grows in nature by attaching itself to the bark of trees, this seemed to me to be the best I could do to mimic natural growing conditions. The challenge for me will be to develop a watering schedule that works. Since this ceramic pot is heavy, it is harder to gauge the added weight of the moist potting media.

After getting the plant repotted, I mixed up a liquid fertilizer that I had on hand at half-strength and watered/fertilized the plant well. I have to admit that I have never fertilized this plant so orchids must be pretty forgiving with fertilization, too. Many sites recommend fertilizing "weakly, weekly" or at full strength once a month. I intend to use the weekly schedule through the summer and fall while the plant is renewing its energy for its next bloom cycle, which, hopefully, will begin late fall or early winter.

Phalaenopsis orchids are widely available and well worth the cost. The next time they catch your eye in the grocery or big box store, you might want to give them a try. Look for one that has a lot of buds (as oppose to fully open blooms) on the bloom stalk and fat, healthy-looking roots. It will give you weeks, perhaps months, of enjoyment from the current bloom. Use this AOS guide as a reminder of how to care for it. The first time you get a re-bloom, you'll be hooked!