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Thinning and spacing

Once again, I’m grateful for these blogs serving as a Sonoma County gardener’s journal. We had very high temperatures at this time last year too, though last year there were also local Red Flag fire warnings. Thankfully, our landscape is still green, though some soils are drying out fast. Now is an important time to dig around in your soil, as it could be surprisingly dry – or moist – depending on soil type, location, use of mulch or other factors.

Recently I’ve been thinking a lot about plant spacing and thinning. Most of us want to grow a lot but have limited space, so we plant densely, hoping to get more production and/or more types of crops. As I mentioned last month, plants that are close together will be competing for water (and nutrients), so more water (and fertilizer), will be needed. But too close spacing can also create several other problems which are important to consider.

Increase in pest and disease is a primary concern from dense plantings. Tomatoes are very susceptible to several fungus diseases. When plants are intertwined they will hold in more moisture and prevent good air circulation, as well as facilitating the spread of fungus spores, making damaging levels of disease more likely to occur. This is true of mildew on squash family members as well. Whiteflies are more prevalent with dense plantings and poor air circulation, and all pests can easily hide in these conditions, making them much more difficult to control.

Ripening of fruiting crops, including tomatoes, beans and corn, can be delayed when plants are too close to each other. They shade themselves, slowing ripening and reducing carbohydrate (sweetness), development. Ear formation in corn can be delayed enough that the tassels shed pollen before there are silks ready in the ears. In general, individual “fruit” from crowded plants will be smaller in size and harvesting may be so difficult that plants are damaged in the process and some crop will be missed.

How far apart should plants be spaced? Most seed packets, seed companies and planting guides offer suggestions, but each garden situation is different and methods of training vining crops, eg, indeterminate tomatoes, pole beans, cucumbers, etc., will vary. When plants are in beds rather than single rows, spacing can be something in between the recommended in-row and between-row spacings offered in these guides. A good place to look is the Master Gardener Planting Guide.

Another issue in more mature gardens is “volunteers” – seedlings that come up on their own from previous year’s crops that go to seed. This can be common with tomatoes, lettuce, arugula, cilantro, parsley, sunflowers and other crops. These can feel like both free plants and our garden’s “children”, so “managing” them can be difficult emotionally, (similar to the difficulty we have thinning extra seedlings of direct seeded crops like corn and beans). Sometimes volunteers can be in the right space at the right time so we can leave them. But often there are too many, (leading to the problems above), or they are in the wrong spot, or of poor quality. If they seem like they could be of value in a different location, transplant the strongest ones to a location where they have the best chance of success. If we leave too many volunteers, crop rotation becomes impossible, in addition to the crowding issues.

The last topic in this realm in thinning fruit. This month is prime time to thin tree fruit like apples and peaches. These trees often set way more fruit than they can ripen well. Too many fruit put such a strain on the tree that it may not grow much or even have enough leaves to create the sugars to ripen the fruit. Pests and diseases can easily pass from fruit to fruit if they are touching. Thinning apples to no more than 2 per cluster, (only 1 if good overall fruit set on the tree), and peaches to a hand span apart, will do the trees a favor and give you better fruit.
Have fun planting and caring for your gardens this May, and give everything the space it deserves to thrive!

Happy May Day!