With the warmth last week and the forecast of another sunny week, you can keep right on planting any and all cool weather crops (peas, lettuce, onions, leeks, all of the cabbage/mustard family, leafy greens, Swiss chard, carrots, beets, turnips, potatoes, etc.). It is still too cool at night in most places to rush warmth-loving plants into the ground, including tomatoes, peppers, squash, cucumbers, melons, corn and beans. And don’t push sweet basil outdoors too early, either: it can’t handle cool, wet weather.
When tomatoes can go outdoors depends on your garden microclimate and how prepared you are to protect them with cloches, floating row covers or coldframes if it turns cool after you plant. Tomatoes are more robust than the other tender plants listed (and some tomato varieties can take cooler weather than others), but that just means they tolerate it, not that they thrive. If it is too cool for growth the leaves often turn purple from temporary nutrient deficiencies caused by the cold. They should recover in warm weather, but it is always better for long-term health and productivity if plants don’t undergo a period of stress while they are youngsters. The general rule is to wait to plant tomatoes until nights are mostly staying above 10oC (50oF).
Other plantings: Corn and beans really should not be sown until the soil is staying above 15oC (60oF). Waiting until the soil is 18oC (65oF) is better, especially for corn varieties with sugar enhanced genes (both hybrid and open pollinated). I always start my first plantings of both corn and beans indoors during the first week of May--the beans in a tray of vermiculite and the corn seedlings in good soil, 1 plant per small pot. You get several weeks head start indoors and by the time seedlings are ready to go outside in 2-3 weeks it will be just that much warmer.
Even if the soil is warm enough, I still start bean seedlings indoors to avoid pillbug damage. Their nibbling on bean seedlings leaves them looking like a row of small green sticks. The jaws of pillbugs are quite weak, however, and once bean plants have germinated and grown for a couple of weeks, the leaves are no longer tender enough for pillbugs to damage them.
I sow sweet corn at least 3 times, 2-3 weeks apart each time, to spread out the harvest so that everything isn’t ripe at once. Sowing in early May, late May and mid-June works well for varieties listed as taking 70-80 days to harvest. For corn that takes longer than that to mature, the mid-June planting may be a bit late unless you are gardening in a warmer inland area.
You can sow peas every month through June to ensure fresh peas into October. I start my early plantings of peas in vermiculite indoors to avoid the main egg-laying period of pea leaf weevil, which is now common in my area. The weevils have one generation a year and only lay their eggs in the spring. Peas planted later than mid-May after the egg laying period is done generally escape damage from the weevil larvae, which eat the nitrogen fixing nodules on the roots. Pea attacked by weevil larvae can’t make their own nitrogen, but still grow well if the soil is enriched with nitrogen sources, such as fish compost, blood meal, alfalfa meal, etc. And while I am on peas, this is a reminder to sow varieties resistant to enation mosaic virus (EMV) for peas that will be present in your garden from mid-summer onward. The virus is spread by aphids and usually shows up in mid-summer. So, to summarize my pea planting plans: In March and April, I plant any varieties I want, but start them indoors and compensate for weevil damage by enriching the planting bed with nitrogen amendments. For peas sown in May and June, I choose EMV resistant varieties, sow them directly in the garden and don’t add nitrogen to the soil since these plants can make their own.
Weather watch: In some years we have heat waves in early May that did a lot of damage to small plants and killed germinating seeds. There isn’t especially hot weather in the forecast for this week, but as always, be prepared to shade seedbeds and small seedlings in a heat wave.
Pest note: If you are growing gooseberries, currants or Jostaberries, you might want to read my May 5, 2017 newsletter on how to prevent damage from two common and damaging pests: Imported currantworm, which eats leaves and currant fruit fly, which wrecks the berries. I am already seeing pinkish, puckered areas on the leaves of my currant bushes that show a currant aphid or two is at work. No matter how weird the leaves look, however, the aphid feeding really doesn’t cause damage and there isn’t anything you need to do about it.