Q: The tomatoes on two of my plants have some disease. I have seen it before, but I have no idea what to do except to wait for it to go away. Each tomato gets a brown spot on the bottom. The spot grows slowly until sometimes it covers a third of the tomato. I am tired of throwing out tomatoes. Can anything be done?
A: Yes, easily enough. Your tomatoes have blossom end rot. It is not really a disease at all. The brown spots are the plants telling you that they need calcium. Your soil has enough calcium, but when the soil gets dry the tomato roots cannot transport the calcium up to the tomatoes. You can cure blossom end rot instantly by watering more frequently or for longer periods of time.
Each tomato that started to develop when roots were dry will get the brown spot. Once there is enough water, all future tomatoes will be fine. Sometimes blossom end rot occurs on just a few tomatoes because the plant was dry only briefly. Sometimes it occurs on one plant but not others because some tomato varieties are more susceptible than others. Always the cure is keeping the soil damp, allowing only the top inch to dry out. In hot weather a mulch will help to hold soil moisture.
Don't throw away affected tomatoes. The brown area is clearly demarcated on the inside as well as the skin. Since the tomato is not diseased, the normal looking parts will have normal flavor.
Q: I have a row of tomatoes in containers. Some are growing well, but some are already starting to lose their lower leaves. What can be wrong?
A: I don't have an instant explanation, but I would start by assuming that the problem is a basic one, not something exotic. I would consider soil, water, and variety first.
Is there a difference in the soil among the various containers? Is it all the same age? Reusing container soil is fine, but the soil structure may change over a few years; it may drain water more slowly. At the same time, nutrients may be used up. Adding fertilizer may become necessary to keep plants healthy.
Presumably all the containers get watered on the same schedule, but they may not all drain water at the same rate. Checking the soil surface will tell you whether some are drying out faster. A container needs water when the top inch of soil is dry.
The watering schedule that was just right in June may no longer be ideal. Since temperatures are higher and plants are bigger, leaves evaporate water faster. Often container plants are most healthy if watered every day in hot weather; containers on a patio or near a wall may even need water twice a day. The dry soil check is the best way to gather information.
Covering container soil with an inch of mulch keeps roots cooler. The tops of plants can shrug off heat if their roots are not overheated. Shading the south side of a container with a board or a piece of cardboard will also keep root temperatures down.
Different tomato varieties grow differently, and some normal aging in lower leaves comes faster to some than others. Some kinds tolerate hot afternoons better. Some are less distressed by cool nights. Early tomatoes age faster than late-maturing ones.
Are the healthy tomatoes the same variety as the worrisome ones? Is this the first year of trying any of the varieties? Some tomato varieties never do well in a particular garden. Some are healthy in open ground but not in a container. Some — like Early Girl, for instance — are not the same tomato that they were ten years ago and may no longer be worth growing.
Master gardener Molly Hackett, whose motto is “Never trust a gardener with clean fingernails,” welcomes your questions. Send them to 1384 Meridian Road, Victor, MT 59875; call 961-4614; or email firstname.lastname@example.org. Please include a garden-related subject line in emails. Hackett writes a twice-monthly Dirty Fingernails opinion piece for the Missoulian.