Winter Cabbage, Irrigation Tips, Beet Leafminers

From now on, continue to be alert for heat waves and be prepared to shade seedbeds and seedlings and to mulch plants to cool the soil. The heat wave earlier this month resulted in injury to unprotected seedlings that is showing up now. Heat injury appears as white or biscuit coloured patches on leaves; whole leaves may turn white in the worst cases. If the stems of the plants weren’t injured, the plants should produce new leaves and recover, but if roots or stems were fried, then you will need to replant. See photos of sunscald on a variety of leaves and fruit.

Which reminds me to remind you that I don’t put everything that might apply to the current date in each message. For additional information, especially if you are new to this series, check my archive of past messages for other notes at the same time of year.

Heat Injury on Seedlings

Winter crops to sow (already!)

If you are planning to grow winter cabbages, such as January King, Danish Ballhead, Langedijker Red or other varieties that take the whole growing season (more than 120 days) to produce full-sized heads, sow those by the end of May. Getting the timing right for these winter crops is a common problem due to conflicting information from seed suppliers. I think the discrepancy in timing is because seed suppliers test grow their varieties in open farm fields that continue to receive dawn-to-dusk sun in the fall, whereas at that time of year home gardens often have significantly fewer hours of sunlight. The low sun angle in the fall means that shade from neighboring trees, houses, etc. blocks early morning and late afternoon sun, cutting down on the number of growing hours per day. Planting schedules for open fields also work fine for gardens in May and June when the sun is high in the sky, but not for gardens in urban or forested areas later it is in the season.

Also be ready to sow Brussels sprouts soon as they also take 90-100 days. Some people get caught every year with Brussels sprout plants too small by fall to make sprouts so if that happened to you, start your seedlings earlier. Timing of Brussels sprouts is tricky because plants sown too early often end up with aphid damage in the sprouts if sprouts develop in August when late season Brassicas often have cabbage aphids. If you sow around the end of May/first week of June, the plants develop sprouts later in September and largely avoid aphid damage. But if you wait too late (after the first week of June) to seed them you can end up with plants that don’t have enough growing season left to make sprouts before winter. If they don’t have their sprouts by the end of October they likely won’t have them at all.

Irrigation tips

Due to the dry weather, people are asking when and how much to water their gardens. Given the huge number of variables involved (temperature, soil type, plant size and density, wind, watering system design, etc.) I can’t make a general recommendation. An old rule was that vegetables need the equivalent of an inch of rain a week, but of course, with drip or soaker hose irrigation systems there is no way to measure that—and anyway, many of us live where water conservation requires us to get by on much less water than that for our gardens.

Clay soils hold water well and one deep watering, weekly may be fine. In sandy soils, which don’t hold water well, it would be would be better to water half as much but do it twice a week. Daily watering is often necessary for seeds and tiny seedlings in dry weather, but for larger plants watering less often is best because we want the roots to follow the moisture and grow deeper. If you are using a drip or linear irrigation system you can’t tell by looking at the surface whether the root zone is moist. The water sinks into the soil in a widening bell shape below the dripper, but it doesn’t spread sideways on the surface, therefore the soil doesn’t look wet no matter how long the system runs. Plant roots grow into the zone of moist soil below the dripper so it is important not to move the water source around once it is established for that crop.

How to check an irrigation system: Run the system for 10 or 15 minutes, then turn it off and wait for an hour or two. Then take a trowel and dig down to the root zone. If the soil looks moist to the full depth of the trowel, try a shorter irrigation time; if the root zone is not moist to that depth, use a longer timing.

Hand watering can be very efficient if done correctly. The main thing to remember is that dry soil absorbs water very slowly: flooding dry soil wastes water because it just runs off. This is where mulches really help because they keep the soil moist enough to take up water quickly. If the soil is dry, just water a little at a time and come back later to water a little more until the soil is evenly moist to the root zone.

How to check hand watering: Set out 5 or 6 straight sided tin cans (e.g., tuna tins) over a garden bed. Using a water breaker or ‘shower’ setting on the hose nozzle, evenly pass it over the whole bed, applying water once to all parts of the bed. Turn off the water and see how much water is in the cans. If it is less than half an inch, make another pass over the bed until it comes up to half an inch. That should be plenty, but you can also check what is going on the same way as for an irrigation system: wait a couple of hours, dig down to the root zone and adjust your watering timing accordingly.

Pest of the month: Leafminers

Eggs of the first generation of beet/spinach leafminer have been laid on spinach, chard, rhubarb, beet, French sorrel. Look for tiny, chalk white masses on the undersides of leaves. When these eggs hatch, the larvae feed between the upper and lower surface of the leaf where they are safe from sprays and predators. You can make a big dent in this first generation by harvesting the leafy greens and using them. The eggs easily wash off the leaves, but if there are small mines where larvae are feeding, pick out the damaged areas—the rest of the leaf is fine. Removing the first generation of leafminers is often sufficient to keep their numbers low for the rest of the season. There are 2-3 generations per summer, but later eggs are more likely to be eaten by lady beetles and other predators. If your plants have been hit by high numbers of leafminers, then sow another crop (not in the same soil) and keep it covered with insect netting or floating row cover to prevent leafminer adults from laying eggs on the leaves. Damage to beet leaves usually doesn’t have much impact on the roots (you can pick off damaged parts of leaves, but don’t remove whole leaves as that will slow root development).

Leaf Miners

May 20, 2019 1:41 PM

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