Author: Erica

Check the Temperature Before You Plant!!

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Several trays of pepper seedlings in quart-size pots sit on a deck getting used to outdoor temperatures.
Pepper plants hardening off

A short post today, in which I make my annual plea to hold off on planting summer vegetables until it’s warm enough. Please – your garden will thank you later!

We have some guidelines on the HGIC website about when to plant vegetables and how to harden them off (get them used to outdoor conditions). Remember, though, that planting isn’t about dates; it’s about temperature. It is not a hard-and-fast rule that your tomatoes should be in the ground by Mother’s Day. What if it’s 40 degrees on Mother’s Day? Bad for outdoor brunch, but also bad for young tomato seedlings.

The round temperature dial of a compost thermometer registering about 55 degrees Fahrenheit.
A compost thermometer is useful for checking soil temps

In general, vegetables that prefer summer’s heat also don’t like spring’s cold. Tomatoes, peppers, squash, cucumbers, and all their friends want soil temperatures over 60F and air temperatures over 50F (including at night). Try to wait to put them in the ground until the forecast shows at least a week of these conditions, with no cold snaps or heat blasts. Of course, spring is full of crazy ups-and-downs (especially this spring) but if you can give the plants a good start, they will tolerate temperature swings better. If a frost is predicted, or really anything below about 45, throw some kind of covering over the plants: heavy-duty row cover if you have it, but a sheet or light blanket will do.

Get to know your garden’s microclimate – if it’s protected from strong winds, plants will tolerate cold better; if it gets a bit of afternoon shade, they will get through high heat with less damage.

You can purchase all kinds of devices to give your plants extra protection, but after trying them all I found I preferred just having some patience. If you do use them, make sure they’re easy to put up and take down – struggling with a complicated shelter in wind and rain is no fun, nor is removing the whole thing again when it’s 85 the day after dropping to 39.

I know, all my plants are huge too, and really want to go outside. But I’m going to wait until it’s time.

By Erica Smith, Montgomery County Master Gardener. Read more posts by Erica.

Spring Crops in Containers

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Lettuce and arugula seedlings growing in a terracotta-colored rectangular planter
Salad greens like lettuce and arugula are easy to grow in various sized containters Photo: Erica Smith

Maybe your first thought on starting a container vegetable garden was “I can grow tomatoes!” Which is great—but tomatoes are a summer crop and it’s not time to put them outside yet. You can start your garden even earlier, though, with spring plantings.

Here are a few of the spring crops you can grow in containers:

The only spring crops I would hesitate to grow in containers are large brassicas like cabbage, broccoli, and cauliflower, and even those could be planted in containers—it’s just that you would only plant one per pot, which might not be worth the effort, unless you have space for a lot of pots, no in-ground garden, and a real love of fresh-grown cabbage.

I’m also not a huge fan of potatoes in containers, because they don’t usually produce very much and it doesn’t seem worth the space and expense when potatoes are so cheap to buy. Nevertheless, I’m going to give it another try this year, just so I can report back here!

Here are some tips on planting spring crops in containers:

  • In some cases it may be more practical to start with transplants rather than planting from seed. This allows you to get the spacing just right and eliminates tedious thinning of extra seedlings. It’s also much faster. But seeding also works fine.
  • Consider the shape of the container when choosing a crop (or vice versa). Crops you want to harvest a lot of, like lettuce or radishes, will work better in a wider container. They also have shallow root systems, so the container doesn’t have to be very deep. Whereas if you’re going to grow carrots, make sure you have a container several inches deeper than the expected carrot length.
  • The usual container growing guidelines apply: use lightweight potting mix rather than real soil from the ground; water frequently; apply fertilizer as needed.

Here are some photos of spring crops growing in containers:

Pea plants in a black fabric grow bag with sticks for them to grow up
Chive plants in a rectangular container
Lettuce, arugula and chard in a raised planter with legs
Seedlings of lettuce and brassicas in a square white raised planter

Photo collage from left (click image to enlarge): peas in a fabric grow bag (a great inexpensive option for lots of crops); chives in a rectangular planter (herbs are wonderful container crops); lettuce, arugula and chard in a raised trough planter on my deck; various spring greens in a keyhole garden, which has an area in the middle meant for creating compost to feed the plants. Except for the trough planter, all of these are from the Special Projects area at the Derwood Demo Garden.

This does bring up a question: what counts as a container? The raised keyhole garden and raised trough planter in the photos are much larger than the typical pot or planter, and may be closer to a raised bed. There’s certainly a fuzzy line between the two types of gardening.

To my mind, a container is an object that holds growing medium more likely to be potting soil than real mineral soil from the ground, and that could sit on a deck, patio, or driveway rather than being situated in a typical vegetable garden layout. I definitely consider my trough planter to be a container, if a very large one. The keyhole garden is an edge case, maybe more of a raised bed the way we use it at the Derwood Demo Garden in Montgomery County, Maryland. But it could be a patio planter, so I’m happy to regard it as a container as well.

In any case, it’s time to get those spring crops growing if you haven’t already! Happy spring!

By Erica Smith, Montgomery County Master Gardener. Read more posts by Erica.

Related information:

Growing Vegetables in Containers and Salad Tables

A container gardening cautionary tale

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In my last post, I mentioned that it’s important to select the correct container size for growing vegetables. In fact, I pointed out that the correct size is nearly always bigger than you think it should be. I think the common error of putting plants in pots too small for them is akin to the instinct that makes us plant them too close together in in-ground gardens. They are just so cute and little when we put them into the ground—how can they possibly turn into hulking monsters with thirsty and enormous root systems? Don’t be fooled! Size up your containers and make your plants happy. (HGIC has a handy set of guidelines.)

It’s not just the size in gallons that matters to successful container selection, though, as my next-door neighbor found out last year. She grows tomato plants in pots on her sunny patio, and has great success. In fact I would say gargantuan success—her plants are huge!

A large tomato plant in a black container, being held up by a wire cage. Many immature green tomatoes are growing on the plant making it even more top heavy.
Photo taken July 22, 2017 – but huge even earlier!

I’m not sure what she does to make the tomatoes grow so tall so fast, while mine are still about half the size in my community garden plot. Soil in pots does tend to be warmer in late spring when the ground temperatures are cool, and my plants catch up over time. Potting soil with plenty of fertilizer included gives plants a fast start, and regular doses of fertilizer keep growth chugging along. Fertilizers with a high percentage of nitrogen produce rampant leaf growth, so that may be part of the equation, though the nutrients must balance out over time since her plants produce plenty of fruit.

In any case, it’s been working out well for her. Until last year. Last summer we had several periods of high winds. The top-heavy tomato plants kept crashing over. In July our neighbors went on vacation and asked us to water their plants, but on the first morning I went over and found the tomatoes on the ground. I ended up creating an arrangement of string, stakes, and cinderblocks to keep them upright.

Three large tomato plant in containers. Cinderblocks are gathered around the containers to help stabilize them. String and simple stakes (like those from a camping tent) are leading from the wire cage to ground to keep the plants upright.

So, container volume isn’t the only consideration—shape matters as well. Containers that are higher than they are wide may not work well with plants that get very tall. My neighbor (who was very grateful for the emergency tomato intervention!) had basically two choices: get new containers (wider, heavier, with a lower center of gravity, like half-barrels), or grow shorter tomato plants.

Therefore, I have introduced her to the Dwarf Tomato Project, and will be growing seedlings for my own use and hers. These dwarf plants, bred for growing in containers, produce tomatoes with real heirloom flavor, but they stay short (heights vary, but most are under four feet). I only have a little experience with these varieties (I figured the Year of Container Gardening was a good time to get more) but like heirloom plants, they’re inconsistent in how many tomatoes they produce over a season; some are prolific and some stingy. So we’ll see how it goes. I’m trying three varieties: Uluru Ochre (which I’ve grown before), Rosella Purple, and Summer Sweet Gold. I’ll also get some full-size plants to mix things up, of course!

The other advantage to dwarf tomato plants is that you don’t need huge containers, but still—I’ll go with the largest ones I own. Other vegetables that grow best in bigger-than-you-think pots include squash (and its relatives like cucumbers and melons), potatoes and sweet potatoes. Size up for success! Also, look at seed catalogs for varieties intended for containers; they will be shorter with smaller root systems and may still be quite prolific while demanding less water. (But remember to water frequently nonetheless.)

Spring is coming, so have your containers ready!!

By Erica Smith, Montgomery County Master Gardener. Read more posts by Erica.

All photos by Erica Smith