Ron Kukawski | Garden Journal: Tomato seedlings are singing the blues - and turning purple


"Why are my tomato seedlings purple?" Though no one has actually asked me that question, I suspect that it may be on the minds of many vegetable gardeners in recent weeks. Perhaps they haven't asked because they believe purple-colored tomato seedlings are normal or because they think that purple tomato plants are really cool. Actually, the second conclusion is the correct one though not in the "really cool, man" sense, but rather in "brrrr, it's cool" terms.

Up until the last few days, the weather this spring has been, for the most part, much cooler than normal, especially the night-time temperatures. I'm guessing that comes as no surprise to anyone other than late-returning snowbirds. Tomatoes, being of tropical origin, do not respond well to cold temperatures. Their growth is retarded at temperatures below 50 F, and there have been many nights, as recent as earlier this past week when temperatures dipped into the low 40s. While slow growth is quite evident with respect to the development of tomato shoots, it is also affecting root development. Root development is especially slow at soil temperatures below 60 F. To make a long story short, cold soils and slow root development interfere with the uptake of phosphorus, a key nutrient for plant growth. The lack of phosphorus uptake prompts the chilled tomato plants to produce the pigment anthocyanin, which happens to be purple.

So, what's one to do with purple tomato plants? Since it appears that the weather pattern is changing and beginning to warm up, the problem should fix itself. However, there are some long-term implications for tomato plants that have been exposed to the cold. In such cases, growth may continue to be slow for some time and result in poor fruit production and distorted fruit. In the meantime, an application of water-soluble fertilizer to tomato plants will help speed recovery.

In the future, it's best to wait until night-time temperatures are consistently above 50 F, and soil temperature is 60 F before transplanting tomato seedlings to the garden. The same rule would apply to other plants of tropical origin, i.e. peppers and eggplant.


Be cool, but get on with these hot gardening tips:

- Re-sow seeds of squash, melons, beans and corn if they have not sprouted within two weeks after initial sowing. The prolonged stretch of chilly, damp weather may have caused the seeds to rot.

- Keep in mind that plant diseases are easier to prevent than to cure. If a disease has occurred on a particular plant in the past, it is likely to occur again. This is especially true for vegetables. For, example, tomatoes are very prone to several diseases, most commonly early blight and leaf spot diseases, and it is a good idea to start this week with regular applications of organic fungicides, such as sulfur, copper, oils, bicarbonates, or biological products containing the bacteria Bacillus subtilis. Even though these are accepted controls for organic gardeners, it is wise to always read and follow label instructions before using any pesticide product.

- Stretch protective plastic netting over the strawberry patch to keep our feathered friends from becoming too friendly with our fruit supply. Though more expensive, it generally works better than some of the gimmicky things, such as reflective foil and rubber snakes, that are often promoted for repelling birds.

- Add a specimen or two of mountain laurel to landscape plantings. These native and shade-tolerant shrubs are now in bloom in local woodlands. Of course, I don't advise anyone to dig those up, but local nurseries will have a broad selection of mountain laurel with many variations in flower color. The flowers remain in bloom for several weeks.

- Put a little sunshine in the shade by planting impatiens in the dimly lit areas of your mind ...err, your yard. Few other plants bloom in so little sunlight. Also, their flowers have a glowing, luminescent quality to them (Much like my writing style, aye! Aye??). If you plant the New Guinea hybrid impatiens, with their attractive variegated leaves, give them a brighter location since they need more sunlight than their shade-loving relatives.

- Plant white-flowered annuals along walks since they show up very well at night and will help guide visitors along the path to your front door. Of course, you could be a little more neighborly and leave a porch light on.

- Go on "pinch your petunia" alert as hot weather takes hold. The growth habit of petunias is strongly influenced by temperature. At cool spring temperatures, petunias will be well branched, compact and loaded with flowers. However, during hot weather, the plants become tall and leggy, requiring occasional pinching back to maintain their floral display.


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