That was very challenging weather for gardeners here in April. We had all that late snow, and, even as I write, the temperature forecast is for more cold weather for a few weeks. I noticed that a national weather service web site forecasts a warmer than average July and August, but really, who knows? I am planting more and more broccoli, choy, rapini, cabbage, spinach, radishes and all those Brassicas. They can handle the cold, wet weather, and are just happy to have day lengths increasing.
Growing all these Brassicas and spinach reminds me how frustrating it is for gardeners when these crops bolt. Bolting is a premature formation of the seed stack (flowering). So, instead of forming big juicy leaves, the little plants suddenly put all their energy into shooting up a big stalk and forming flowers. Hot weather and lack of water or nutrients will encourage bolting. Once these plants start bolting, there is no turning it back. It is most frustrating if the plant is only 4 inches tall and never even tried to make big leaves. Sometimes, when gardeners buy plant starts at a nursery or grocery store, these seedlings have already been stressed by lack of water or nutrients and they will bolt as soon as you get them home. Choose nurseries or markets that know to care for Brassicas or spinach seedlings properly before you purchase them.
The same goes for lettuces. Most lettuces are easily stressed by hot weather, especially leaf lettuces. The romaines are not as susceptible to bolting. The Black Seeded Simpson leaf lettuce has the best results in hotter weather. Northwest gardeners know that summer lettuce salads are hard to grow here. Planting in a shady spot in the garden can help keep lettuces growing, but remember to water them often. For summer green salads choose heat tolerant greens like New Zealand Spinach, sorrel, or a bolt resistant hybrid lettuce. When you do notice your lettuce plants bolting this summer, harvest all of them. If you keep almost bolting lettuce in the refrigerator for a day or two, it will loose that bitter taste that forms as the plant begins to bolt. You may want to allow a couple of the best plants to flower and set seed for future plantings.
Another favorite crop in a spring garden is cilantro. This herb, like parsley, loves cool weather. But when the weather gets hot, cilantro will bolt. Either plant it early enough to get leaf production before hot weather, or just plant it for production of the seeds (called coriander seeds). I always save coriander seeds and then plant again in October. It will often winter over and give you delicious leaves in March and April. Watch out for those slugs though as they love cilantro leaves.
The bolting of basil is another story. Basil is a hot weather crop. The reason it bolts is when it is stressed by not enough water or nutrients. Never let it dry out. Plant in a less windy spot. Give it a good drink of fish fertilizer every couple of weeks, or some other extra nitrogen source. You can keep pinching off the basil flower heads as they form. This encourages branching and you can get more leaf production.
Another tricky crop is Florence fennel because sometimes it will bolt before forming the large bulb at the base. Some cultivars are sensitive to day-length, fluctuating temperatures, lack of water or transplant shock. Choose a NW cultivar that has been developed to resist bolting, though none is perfect. Pleasantly warm summers with good soil fertility and plenty of moisture are ideal conditions for fennel.
Onion varieties vary widely in their susceptibility to bolting. Some are especially prone to bolting if rapid early growth is followed by a period of cool weather. Again, keep these watered and check your soil fertility. Disease will also stress the plants. Watch for the onion root maggot or onion molds. Always rotate where you plant the onion family. Expect the plants to decline after the days begin to shorten, which is in July here in the north. You will know when it is ready to harvest because the stems will fall over and the shoulders of the bulb will be protruding. If you see some plants trying to form early seed stalks, break them off or step on them so they will lie flat. You can still enjoy eating ones whose seed stalks began to form, but those should be eaten quickly, as they do not store as well as the other bulbs. Of course, if you want to save seed for next years plantings, leave one or two onions to bolt and then carefully collect the seed heads in Late summer or early fall..