Ask The Gardener: Dogwood shrubs, tulips, preventing weeds and more

Everybody Gardens editor Doug Oster gets asked a lot of questions. A lot. And he doesn’t mind offering gardening advice. But rather than just limiting those answers to the person who asked, we thought it might be a good idea to share that wealth of knowledge with everybody.

There are three ways to send in your questions:

Email askdoug@535mediallc.com
Submit your question on our “Your Garden” section of our site
Send us a message on Facebook.

(The questions may be lightly edited for grammar/clarity/etc.)

Question 1: Dogwood shrubs

Bob: I am seeing an increase of these spots on the leaves and believe they are a fungus that might kill my dogwood shrubs. I lost one last year and was told there is very little that can save the plant once the fungus gets hold of it. What can I do to eliminate the fungus?

The small plant is what survived from last year and after the deer chewed on it this spring. The larger plant is new this spring and was doing fine. Thoughts on a treatment for my dogwood shrubs?

Doug: It looks like a fungal issue to me, probably septoria leaf spot. It’s hard to avoid with the amount of rain we’ve had, the plants are susceptible to the disease, and wet, humid conditions don’t help.

Sanitation is the No. 1 way to deal with the disease as it overwinters in the leaves. Be sure any foliage is cleaned up from underneath the plant now and through the end of the season. Also Serenade (available here) is an organic fungicide that will work to keep the disease in check. When things dry out, the plant should rebound. The disease won’t kill dogwood shrubs, but it makes a beautiful cultivar like yours turn into a bit of a mess. Wait it out and in a normal season you shouldn’t have to worry.

Question 2: Tulips

Marcia: I received some tulips at Easter and was told not to plant them because they were genetically modified and would not bloom. Have you heard of this? How do you know when you buy tulips at Easter whether they would bloom next spring?

Doug: There’s nothing about them being genetically modified that I’ve ever heard of. They don’t bloom well regardless when grown that way. No harm in planting them though, maybe you’ll get a wonderful surprise in the spring!

You don’t ever know if they’ll bloom in the spring; it’s always a gamble. In general I’d give any of them about a 30 percent chance of blooming again in the spring, but that’s just a guess.

If it was me, I wouldn’t bother. I would buy some bulbs in the fall, plant them and enjoy the spring blooms. Even those will usually be good for one or two seasons and then fade away.

The key to growing perennial tulips is choosing varieties that are known to return like Darwin or species tulips (smaller, but wonderfully colorful). They should be planted in a spot that dries out in the summer. If they get lots of water, they will not be happy.

Question 3: Preventing weeds

Mary: I laid down weed fabric and stones, and the weeds got through. I have RoundUp, but I won’t use it because the ingredients cause cancer. Is there anything else I can do before laying the weed fabric to prevent the weeds? Should I mulch then lay down my lucky stones?

Doug: It might not be that the weeds got through; sometimes weed seeds are on top of the barrier after a season or two. It’s one of the biggest problems of using weed barriers. If you don’t want to remove the current barrier, use an organic herbicide like Avenger. It’s safe and will deal with the weeds. At this point since you have stones over the fabric, that would be the easiest way to deal with the problem.

Question 4: Blossom end rot

Ruth: What is best way to treat blossom end rot on tomatoes in pots? I used new potting soil and feed with product that has calcium. It’s better than last year but not great. Frustrating!

Doug: We’ve had a lot of blossom end rot around this year. It’s usually not a calcium deficiency. The plant can’t uptake the calcium. It’s due to the the deluge of rain and then drying out. This is the first year I’ve had it in at least a decade. Mulching to keep the soil evenly moist will help. The good news is that it often will be on the first tomatoes, but not later in the season. Also, sometimes a tomato can heal the blossom end rot at the end of the fruit.