The Garden Guy answers your questions

Tree watering bags will keep the soil moist and the roots alive.

By Bruce Bennett

If you hadn’t noticed the weather, welcome to the ‘Dog Days of Summer.’ 

Traditionally, the Dog Days refer to the hot, humid days of summer, usually July and August (but, this year let’s toss in June as well). 

These days were heralded by the rising of Canis Major’s constellation (Large Dog) and its brightest star ‘Sirius,’ also known as the ‘Dog Star.’ 

In the Northern Hemisphere, the Greeks and Romans believed this astrological sign was connected with heat, drought, lethargy, fever and bad luck when both men and dogs were driven mad by the extreme heat. Luckily, we have advanced to air conditioning! So much for the issue, no one asked about. So, let’s move on to some of the actual questions I’ve received over the past few months.

Q: I’ve noticed some odd patterns on the leaves of my Elm Trees that I had not seen in previous years. Are these caused by the summer’s unusual heatwave, insufficient watering, or what?  

The large of a sawfly are feeding on the leaf of an Elm tree.

A:  Strange patterns on your trees’ leaves might catch your eye. Veins border these patterns in a leaf and between the top and lower layers of the leaf. If you’re lucky, you may even be able to see a little wormy thing within the damaged areas. Your particular situation is the work of the Elm leaf miner, which are the larvae of a sawfly. Many insects use this form of feeding. I generally see mine in spinach leaves. As the wormy beastie is inside the leaf, traditional insecticidal sprays have no effect. 

Instead, pick off the damaged leaves on smaller plants and put them in your yard waste container, NOT your compost pile. For larger plants, such as trees, a spring spraying of the new leaves will keep damage to a minimum. Luckily, leaf miner problems are not plant killers.

Q:  This time of year, I see many green bags around street trees in my new neighborhood. How do they function and can I get them for my yard?

A: You are referring to watering bags, AKA Gators or Treegators. Until a young tree is around five years old, most of its roots are close to the surface and under the trunk. That’s when a tree watering bag will keep the soil moist and the roots alive. Deepwater saturation promotes deep root growth and reduces transplant and drought shock. However, this only works if you remember to fill the bag with water once a week. 

A single bag is suitable for a tree up to four inches in diameter.  

Older trees in the 4′ 8″ diameter will do better with a double-bag set-up. The typically-noticed green watering bags are about 25″ tall x 15″ wide. There is also a (6″ x 36″) donut-shaped bag for lower profiles, especially under Japanese maples. Water should be added to this smaller one twice a week in the weather we have been experiencing this week. Don’t forget to take the bag off the tree in winter; otherwise, you can run the risk of bark rot and death.  

Q: I have several dahlias in my yard that grow well but have had little to no blooms on them for the past two years. I believe more sun is needed, so I’m building a bed for them in a sunny location. Can I transplant them now? If not, when should I do it?

Dahalias need to finish out this year’s growth cycle before they are transplanted.

A: Allow your dahlias to finish out this year’s growth cycle. They need as much energy created by the leaves as possible pumped into the tubers. 

Once the plant has died back to the ground in autumn, you can dig them up and replant them elsewhere. If they are cultivars you particularly enjoy, take a bit of caution and allow some to dry a bit, brush off clinging soil and write the specific cultivar on the tubers, so you know who is who next spring. 

If the tuber clump is enormous, this is an excellent time to divide it. Finally, tuck the processed tubers away in a frost-free area of the house. 

I tend to put mine in a box with crumpled newspaper or sawdust and place the container on the house wall of the garage. When spring arrives and the soil has time to warm up a bit, amend the soil with compost, dig one-foot deep holes, place the tubers and fill the holes about a quarter full. As the new shoots grow, add more soil gradually until you reach the ground level. Remember to protect against slug and snail predation using an old paper towel or TP rolls.  

Q:  Some insect has been borrowing into my apples for the last few years and ruining them. I’ve had people tell me I have apple maggots and or apple codling moths. How do I tell them apart? Any ideas what I have and how to get rid of the problem?  

A:  This is a pretty easyidentification to make. If you cut open one of your ripe apples and find a reddish frass (bug poop) filled tunnel that goes to the center of the apple and then out of the apple, you have an Apple Codling Moth issue. If the cut apple shows many winding tunnels throughout the apple, you have an apple maggot (fruit fly) problem.

 All these “worms” can overwinter in your yard in the cracks of tree bark or in the soil around an apple tree. So, your first line of defense is to pick up any apple within a few days of its fall from the tree. That will prevent the worm from leaving the apple and burrowing into the soil to overwinter. Dispose of them in your yard waste container. This one action on your part should reduce apple damage by more than 50%. 

The adult insects emerge from the ground from early May through August. Spray the newly forming apples with an organic insecticide (aka spinosad ‘Entrust’) or barrier (aka kaolin clay ‘Surround’). There are undoubtedly other remedies.  

In all cases, remember to read the directions and warnings on the container. A different approach would be to place the growing apples in plastic sandwich bags and zip the seal on either side of the apple stem.  

Consider reading the apple problems section of WSU Extension Hortsense at HortsenseHome.aspx or the Pacific Northwest Insect Management Handbook at

If you have a gardening question or an article topic you care to discuss, feel free to contact me a [email protected]


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