Monday, May 2, 2016

Grafted Tomato Plants

           When I first heard of grafted tomato plants, I thought: Grafting? Of annuals? Really? Grafting woody perennials, yes. The time, attention and effort required to produce a successful graft rewards us with years of fruit (trees) and/or beauty (think: roses). But all that work for the tender stems of tomato plants that only last a season? Yet grafted tomatoes, watermelon, cucumber, eggplant, and peppers are catching on worldwide  -- and for good reason.
         The process of grafting annual vegetable plants is theoretically simple. Take a plant with a strong rootstock, slice off its green top at an angle then slice through the stem of the desired top-growth plant (scion) cutting off its roots. Mate the sliced ends of the two plants and clip them together until the slice heals.
         “The plant can begin to draw nutrients within 10 seconds,” says Peter Zuck, vegetable product manager at Johnny’s Selected Seeds in Winslow, ME, which sells grafted plants, “but the after care of the newly joined seedling is critical.”
         As soon as the graft is made, plants must be kept at just the right temperature (70-74F) and humidity (80%-90%) and remain in low light to prevent top growth while the graft heals completely.
Root stock cut with tops being added
         “Some people incorrectly think of it as similar to genetic engineering,” says John Bagnasco, managing partner at SuperNaturals Grafted Vegetables in Vista, CA, “but it’s not at all.”
         Grafting has been a horticultural practice for centuries. The Bible mentions grafting olive trees in the book of Romans. The Chinese grafted the strong roots of wild tree peonies to their favorite cultivated stems in the 9th century.* But grafted annual vegetables and fruits are a relatively recent addition to the horticultural pantheon.
         “The Japanese began grafting them about thirty years ago,” says Bagnasco, who notes that Japan struggles with depleted, disease-prone, and challenging soils. “They have to graft to get them to grow.”
         Additionally, the 1997 Kyoto Protocols, which outlawed methol bromide used to control soil-borne fungal, bacterial and viral diseases, prompted an upsurge in the use of grafted annuals among its 197 signers, who needed an effective alternative to the pesticide.
          “Almost 100% of the watermelons grown in Mexico are grafted now,” says Zuck.
Graft clip over where the two sliced stems meet
         In 2011, it was estimated that 1 billion grafted fruiting annuals were sold worldwide. In 2015, the number was 1.5 billion.
         “Most were watermelon plants and most were sold in China,” says Bragnasco.       
         In addition to disease-resistance, the grafted plants tend to stand up to the kinds of climatic and regional stressors -- soil salinity, temperature extremes, short seasons, and lower light -- that can doom a vegetable garden, especially that succulent emblem of summer: tomatoes.
            “Tomatoes don’t care for the broiling hot weather we have in summers around here,” says John Campbell of Annapolis, MD. Campbell has been growing grafted tomatoes in his home garden for ten years. “If the weather stays above 90 degrees for more than five days, they slow up on production. What I have found is that the grafted tomatoes suffer through this rotten summer weather with no problems, and I have not had any problems with disease.”
         In addition to withstanding stressors, grafted vegetable plants can produce well despite less than optimal light. Most vegetables require six to eight hours of direct sunlight a day to fruit well.
         “I had a small lot in Belfast [ME] with mature trees,” says Zuck. The tomatoes got about five hours of direct sun coupled with dappled sunlight and shade the rest of the day. “I found that the grafted plants helped me overcome that. They were much bigger and more productive than the non-grafted plants.”
         The plants produce anywhere from twice to three times the fruit, and they are exceedingly hardy,” says Campbell.
         Another advantage for the home gardener with limited space is that grafting bypasses the need to rotate crops, a common practice used to avoid recurring soil-borne problems. Although grafted vegetable plants are obviously more expensive than non-grafted, for many home gardeners it’s worth it.

* An Illustrated History of Gardening, by Anthony Huxley, Lyons Press, 1978.

Thursday, April 28, 2016

Two great Montgomery County events this weekend

Hear more from the Montgomery County Master Gardeners at this link:

Monday, April 18, 2016

Edema on pepper seedlings

One of our demo garden MGs brought a pepper seedling leaf in last week with small bumps on the bottom, near veins. It looked healthy otherwise and didn't have apparent active insects. Then the same thing happened to my pepper seedlings, so I decided to look it up.

The issue appears to be edema, which is an abiotic problem usually resulting from overwatering. Basically, the plant takes up water faster than it can use it. With a mild case like this, the simple solution is: don't water as much! If it persists I may also try adding calcium as a deficiency of that mineral can also be a factor.

Here is an article on edema from U. Conn. (doesn't mention peppers specifically, but I made the connection through a hot pepper growing forum, and the many photos similar to mine on the web also help with diagnosis). And on UMD's HGIC, results of edema at a later stage.

Seedlings are best watered deeply and then allowed to dry out on the surface before watering again. This also helps keep fungus gnats away. Make sure your pots have adequate drainage holes and water doesn't sit in the trays.

My pepper seedlings are beautiful and large! Too bad it'll be another month before I feel comfortable planting them outside...

Wednesday, April 13, 2016

New pest of garlic, leeks onions found in PA

Breaking news from Jerry Brust, UME IPM Vegetable Specialist:

"Hello Everyone...another new pest--the Allium (or onion) leafminer has been found in Pennsylvania. It seems to be worse in organic systems and in home gardens, but it is something we should watch for over the summer and fall. It seems to like leeks the best, but will infest any allium spp. Its population appears to build through the spring and summer and can become quite high on some farms that do not spray any insecticides."

Link to a full IPM report with photos from Penn State Extension: 

The report is for commercial growers (organic and conventional). Home gardeners in MD should focus on scouting for this pest and reporting any finds to HGIC. Covering early spring  alliums with floating row covers will help exclude the allium leafminer and other pests, such as onion maggot.

Friday, April 8, 2016

Effects of light, cold, and wind

Every once in a while we gardeners get a clear illustration of the effects of environmental factors in the growth of plants. Here are two that happened at my house recently - I'm sure you can come up with lots of additional examples.

I seeded 'Pomegranate' lettuce in March and transplanted the seedlings into 2-inch cells when they had first true leaves. Then, due to space issues, I put half the seedlings under lights inside and half out on my enclosed back porch (it has vinyl windows that slide down over the screens, so is protected from wind, but only a few degrees warmer than outside). The back porch seedlings got direct morning sun but no additional light. Here's the difference a couple of weeks later:

back porch

The back porch seedlings will be fine for transplanting in another week or so, but they'll take some time to catch up to the others. Both the warmer temperatures inside and the close-up light over the seedlings made a huge difference.

Another more severe effect happened during that day-long blast of frigid wind on Tuesday. I went out in the morning and walked under the arbor where my Siberian or kolomikta kiwis grow (different species than the larger hardy kiwi, Actinidia arguta, but with a similar zone range, i.e. perfectly hardy in 7a). Everything looked fine then, but when I next looked in the late afternoon, nearly all the leaves were badly desiccated by the persistent wind - or frozen, or both.

They still look like this today. I'm hoping to see some recovery in the next week, but it's possible the plants will lose the leaves and flower buds. They've been doing fine for several years, so I guess we've just never had that particular kind of wind at this time of year (or stage of leaf growth) before.

I must add that the Derwood demo garden team was also blasted by the cold and wind on Tuesday morning - our first workday of the season! - but at least we could go inside to warm up. No such luck for plants.