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All Past Questions and Answers Library   |   October 2009

This month's questions concern:

Any Benefit From Coffee Grinds
Propagating Sansevieria (Snake Plant)
Floating Row Covers & Plastic Mulch
Growing Vegetables Large
Tomatoes With Thick Skin
Removing Bark From Tree

Please scroll down to read the answers.

Question #1:  Any Benefit From Coffee Grinds

Question:  What is the benefit of using coffee grinds in one's garden?

 Eddie Collister, Saint-Hubert, Quebec, CA


ANSWER:   Hi Eddie! This really is a loaded question! I can feel my email box filling up with comments from this already!

OK - so let's tackle this heated debate of coffee grounds.

First of all, yes, coffee grounds have been found to have some benefits. But before we go any farther, let's take a closer look at this.

About Acidity

Many people will tell you that coffee grounds are very acidic and to use them only on alkaline soil, or on acid loving plants like azaleas, and while it is widely thought that the grounds are acidic, it has been shown that most of this acidity is removed in the brewing process.

Used grounds are essentialy neutral, and using them on plants, or composting them with other materials, will buffer any minor residual acidity.

A controlled chemistry experiment on the acidity question was held, and this is what it had to say:

"Roasted coffee is fairly acidic, but it appears that almost all of the acid is water soluble and is extracted during brewing. Used grounds have essentially neutral pH, although the coffee beverage produced is rather acidic.

The measured pH of used coffee grounds was 6.9, with a significant amount of buffer capacity - adding the coffee to either acidic or basic solutions drove both towards neutral pH. The exact pH of used grounds will depend on the pH and alkalinity of the water used in brewing, but with any potable water, used grounds will be close to neutral pH."

Other people will argue this point, so really I think, the best way to be sure is to take your used coffee grounds and use a home soil test kit and see what the pH is. That way you know from your own coffee and water samples exactly what the pH is. If it registers a high pH like around 5.0, then you know you will have to dilute them till they reach a less acidic level.

I'm not trying to not give an answer, but it is the safe way to go so you don't burn the heck out of your plants inadvertantly!

About Worms

Some people will tell you that coffee grounds will attract worms. Anecdotal evidence suggests that worms are very attracted to them so you can feel free to use them in around your plants or in vermiposting (worm bin) situations if you want.

About Nutrients

Also, you may hear they are good as a fertilizer, and yes, used coffee grounds can be used as fertilizer in your garden because they have nitrogen and micro nutrients in them. In fact, coffee grounds have a carbon-to-nitrogen ratio of 20:1, or 1.5% nitrogen content, roughly equivalent to that of grass clippings.

After brewing, coffee grounds contain up to 2% nitrogen. For composting purposes, consider coffee grounds "green" material similar to grass clippings.

There�s also a lot of Magnesium and Potassium, both of which plants really like; but not a lot of phosphorus (the nutrient used for flowering and fruiting), nor a lot of calcium.

If you don�t drink coffee or need a lot of grounds, visit your local Starbucks. This company has a policy of giving used grounds to customers for use in home gardens.

Slugs and Snails

Some people claim, though I have never personally seen this, that the grounds are helpful for eradicating slugs and snails.

One study by the USDA showed that they are effective against slugs. Other studies have shown no big difference with the use of grounds. The caffeine in the grounds and acidity are thought to be responsible for repelling the slugs. There is a lot of debate among gardeners on this benefit. Some believe it works, while others think does not make a difference.


There are several ways to use grounds in your garden. You can sprinkle the used grounds around the plants that are already in your garden. Just sprinkle the grounds on top of the soil and water them in. This method allows the nitrogen to be slowly released into the soil to nourish your plants. Be sure to sprinkle the grounds lightly over the soil. Don�t just dump a pile around the plants. This can cause the grounds to cake and this will actually cause them to crust over, preventing moisture from getting to the roots of your plants.

Another method of adding grounds to existing plants is to lightly work them into the soil around the plant. Take a bit of the grounds and a small garden spade. Lightly dig the grounds into the soil. Dig the mulch into the first 1 inch (2.5 cm) of soil around your plants. This will help nourish the plants and will prevent the caking that can happen when you just add the grounds to the top of the soil.

You can add grounds to new plant beds prior to planting. When you are preparing the soil for planting, add the grounds. Tilling the grounds into the soil will produce the best results. This will nourish the soil without causing the grounds to cake. Till the grounds into the first 6 to 8 inches (15-20 cm) of soil as you prepare for planting. Add the plants and backfill with the soil and grounds mixture. Water the beds well to help release the nitrogen into the soil.

Bottom Line

I think the bottom line with all this is, use them as you wish and watch the results. With so many myths floating around, the only way to really know for your own garden, plants, and situation, is to test, and see the results.

I hope this has answered your question and I have provided you enough information to use your coffee grounds if you want to! Good luck!!

Question #2:  Propagating Sansevieria (Snake Plant)

Question:  I have a question regarding propagation. I have tried the leaf cutting method with the snake plant but this never worked for me, the cutting just gets soft and soggy. What am I doing wrong?



ANSWER:   Hi Sakina! I'm not really sure where you are going wrong; if you are taking the stem cuttings correctly, what type of medium you are using, or how moist you are keeping them, so let's just start from the beginning and go through it... OK?

Leaf propagation of Sansevieria (S. trifasciata), also known as a Snake Plant, or Mother-in-Law Tongue, is pretty easy. When you use leaf cuttings, one of the tricks is that they must be in a sand medium to keep the end from rotting. If the specimen is variegated, the variegation will be lost on the new growth coming up. In other words, the original leaf cutting does not become a permanent part of the propagated plant, but will simply atrophy.

Here's How To Do It

To grow a new Sansevieria, it will be necessary to take a fully grown leaf and cut it into pieces about 3-6 inches (8-15 cm) long, keeping careful track as to which end was closer to the root, because if you get them turned upside down, they won't grow. Many people put a mark towards the top of the cutting so they can remember which side stays up when planting them.

The cuttings should be placed in a warm airy location to heal for a few days.

When planting the leaf-parts, use well draining succulent, sandy-type soil, moistening it slightly.

Several leaves can be put into each small pot, making sure to bury the root-end of the leaf. Planting them upside down is wasted effort as they will not root.

Keep the pots out of full sun, instead put them in bright, indirect light until roots form.

Kept at 70° F (20° C), roots should form in 4-6 weeks, depending on the species, lighting conditions, etc.

Until roots form, water sparingly. When the first leaves emerge, they will not necessarily look like the parent plant. Some species of Sansevieria have a juvenile form of leaf, with the mature form appearing later on the same plant.

I hope you try again, and this time you are more successul!

Question #3:  Floating Row Covers & Plastic Mulch

Question:  As a novice, could you please tell me what a floating row cover is, also what is plastic mulch?

 Alan Robson, Blyth, Northumberland, England

Click Image For Larger View


ANSWER:   Hi Alan! This is a very good question!

I have put an image of a floating row cover and plastic mulch (shown respectively) in the picture above. If you click the image, you will get a better view of them.

Floating Row Covers

Floating row covers are made of a breathable white cloth that lets light and water through (not just plain clear plastic) and they literally "float" over the plants as the wind and air move them about. You can get them at most garden supply catalogs or nurseries.

They shield plants from frost and pests while letting in sunlight, water and air.

They Can Also:

Extend early and late growing seasons by providing frost protection down to about 28° F (2.2° C)

Aid germination by keeping soil moist

Prevent crusting of soil due to hard rains

And shield plants from insect pests, including virus-carrying aphids

Covers usually transmit 85% of sunlight, allowing strong plant growth. Soft polypropylene fibers are less abrasive to tender plants than polyester covers.They last about 20 weeks (example: 5-week periods for four seasons).

Cut to fit over your plants as shown in the picture by using pvc pipe that is bent over the plants to form "hoops", or use wooden stakes set into the ground at spaced intervals. Basically you can use anything you want, just as long as it keeps the material up and off the plants. Remove the cover when daytime temps are consistently above 80° F (27° C).

Plastic mulch

Is used to suppress weeds, conserve water, and in some cases, provide extra warmth for plant roots. Certain plastic mulches also act as a barrier to keep methyl bromide, both a powerful fumigant and ozone depleter, in the soil.

Crops grow through slits or holes in thin plastic sheeting.

Plastic mulch, like everything else, has its pros and cons. It can be hard to put down (and keep down) when the wind is blowing, it doesn't let rainwater into the soil, and at the end of the season there's a lot of plastic for the landfill, although I've heard some of it is recycleable.

Now when it comes to vegetable garden mulching, you should try and match the mulch to the crop, weather conditions and soil, because university field tests have shown that mulch can increase (or decrease) yields by as much as 30%.

Your Crops

Keep in mind, not all vegetable plants like the same growing conditions. Heat-loving peppers, tomatoes, eggplant and melons are great candidates for plastic mulch. Applied in early spring, the plastic will raise soil temperatures and help warm the air around the plants. But most plastic mulches are not water permeable. This means that as the season progresses, your plants may go thirsty. Inadequate moisture can stress your plants, lead to blossom-end rot problems on tomatoes, and diminish your overall harvest, therefore, installing a sub-surface irrigation system beneath the plastic mulch may be necesssay.

You might also consider removing the plastic in late July and replacing it with a water-permeable mulch such as straw, newspaper or grass clippings. This mulch will allow rainwater and overhead irrigation to get down to the root zone, and will also help retain moisture.

Cool-weather crops such as broccoli and greens don't want the extra heat from a plastic mulch. They'll be better off with straw, shredded leaves or newspaper. These mulches can lower soil temperatures by as much as 20 to 25 degrees, which may keep cool-weather plants producing right through the summer�s heat.

Also, if you live in a hot climate, use plastic mulches judiciously. High soil temperatures can stress your plants and burn up organic matter. In hot climates, most crops will be happier and more productive with a soil-cooling mulch such as compost, shredded leaves or straw. Conversely, if you live where summers are cool and wet, using a moisture-retentive, soil-cooling mulch could be disastrous. You may find your plants stunted from the cold, turning yellow from too much moisture, and being chomped by an army of slugs.

Make sure to let the soil warm up and dry out a bit before applying soil-cooling mulches. Depending on where you live, this may mean waiting until June or even early July. Consider using a plastic mulch during early spring. It will raise the soil temperature and also help dry out the soil.

Lastly, any heavy, wet soil should not be covered with a moisture-retentive mulch. Nor should you cover a dry, sandy soil with plastic. So overall, take a minute to consider your garden's soil conditions before selecting a mulch.

Question #4:  Growing Vegetables Large

Question:  I really really want to know what to put into the soil to make a vegetable grow large! I have been trying to grow muskmelon and the little buggers won't get any bigger then a large softball. What can I do to get them to grow like the one's you get in the store? My climate zone is 5 so does that have something to do with it?

 Genelle Fahey, Fenton, Michigan, USA


ANSWER:   Hi Genelle! I understand your frustration!

Reading about your area, it says that Fenton, MI climate is mild during summer when temperatures tend to be in the 60's F (16° C).

The warmest month of the year is July with an average maximum temperature of 82° F (28° C), with temperature variations between night and day tending to be moderate during summer.

With that in mind, you have to remember that Muskmelon, or what some people call Canteloupe, are heat and sunlovers, and the problem with locations like yours is lack of heat. You can overcome this to some extent by growing melons on black plastic, which draws heat from the sun during the day and conserves it at night.

Plastic also holds down weed competition, and prevents evaporation of moisture. Next year, grow your melons on large sheets of heavy solid black plastic. You will retain more heat, and not have to water as much because there is so little moisture loss to evaporation.

The other thing melons require is a highly enriched soil to grow vigorously and produce fruits of any size. You can tell how well a melon plant is going to produce just by looking at the leaves. Big, healthy, dark-green leaves mean good melons. Scraggly, weak plants mean little or nothing.

Add lots of good compost and a balanced organic fertilizer, like Dr. Earth, to the soil. Buy a little black plastic, and give it a try.

Lastly, if it looks like your vines are producing many melons, you can always remove a few so that the vine only has to grow and provide nutrients for 1 or 2 melons and not several.

Let me know how it goes next year, I would love to hear back!

Question #5:  Tomatoes With Thick Skin

Question:  Why does the skin on my tomatoes get so thick?

 Mary Tarantola, Tannersville, Pennsylvania, USA


ANSWER:   Hi Mary! This happened to our tomatoes this year too because of our extreme heat fluctuations. That said, there are 2 main reasons for getting a tough, thick skin on your tomatoes.

1. Varietal differences

Many of the more common hybrids have tougher skins bred into them for shipping purposes. So varieties like Roma or Plum tomatoes genetically have thick skin.

2. The Weather

Dry or very hot summers tend to produce thick skinned tomatoes. Even when watering the garden, the sun is hotter and the air is hotter through the days, resulting in thicker skins. Inconsistent moisture levels in the soil or excessively high air temperatures contribute to the problem as the plants try to conserve moisture.

So weather and varietal issues are happening to you, and there really isn't much you can do, except grow more tomatoes next year and hope for a bit cooler temperatures!

Question #6:  Removing Bark From Tree

Question:  Hi, I have a property in Turkey with a olive tree growing in the garden. We have cut the growth back last October but it seems to be growing even faster. Is it possible to cut out a ring around the trunk leaving a small strip of bark to slow it down or would this kill the tree?

 Derek Willam Ward, Uttoxeter, Staffordshire, UK


ANSWER:   Hi Derek! This is an interesting question because olives (Olea europaea) are known to be fairly slow growers.

Young trees do tend to put on height fairly fast, but then slow down as they fill out.

Overall, I would highly recommend against this. Any break or tear in a tree's bark disrupts the flow of vital fluids and exposes wood to invasion by disease and decay microorganisms, which the tree must then expend energy to deal with.

A trunk wound does not always cause loss of branches or foliage, so the consequences may not be fully apparent until too late. A wound in the trunk of a tree is serious since it cannot be repaired and will almost certainly result in future decay and loss of tree strength.

I don't know how severely you are pruning your tree, or how old it is, but keep in mind, pruning encourages and stimulates new growth. So if you really cut it back hard, and the tree is fairly old, you will get considerable growth very quickly because a mature tree has a large, established root system and can direct a lot of energy toward new growth if a lot was removed.

My suggestion to you is to lightly prune once a year for shape, and realize that olive trees get fairly large - up to 30 feet (9 m). You can keep it pruned shorter if you wish, and you can dictate its shape, but it will be a yearly event.

I hope this helps, good luck to you!

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