How many plants to plant (in vegetable and herb gardens)

One of the most common questions asked by novice vegetable and herb gardeners is “How many?” That is, how many of each plant to put in, so that the harvest will be enough to make dinner but not so much that you’re frantically trying to find homes for a major surplus. When you plan an ornamental border, there are design guidelines that talk about groups and masses and specimen plants, but food gardens (although they can be beautiful) are not planted with aesthetics primarily in mind. So how to make these choices?

You can find plenty of guides online for, say, planning a garden for a family of four. These tend to assume that your garden is large and that you want to supply all or most of your needs from it. Which is great if that’s your goal, but I don’t find that many of the busy urban and suburban gardeners I talk to mean to skip the supermarket produce section entirely. The online guides will also measure the planting in feet of row; if you grow in the square footage of raised beds, you’ll have to do some recalculation. Growing in these kinds of high volumes probably also requires food preservation, whether by freezing, canning, or some other method.

Your garden does not need to be planted in long, long rows to be productive

Most of us find the answer to “How many?” through trial and error, and frankly you probably can’t avoid that entirely. You’ll err on the side of not enough for some plants, and too much for others, and will serve some salads featuring a handful of lettuce or one small cucumber, or get to know your neighbors when you have tons of extra tomatoes. But there are ways to plan.

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The Ripeness is All (or Some)

As Dr. Spock famously said about parenting: “Trust yourself. You know more than you think you do.” This is equally true about gardening, even for beginners. People sometimes ask me when they should pick vegetables, as if it was a total mystery, and I generally reply that they’ll know it when they see it, especially if it’s a crop that’s commonly available in markets and grocery stores. If not, a quick online search or a look at the seed packet or catalog may enlighten you. Yours may not achieve the shiny perfection of the catalog models, but it’ll be recognizable. There are exceptions to this easy-to-tell model (melons are notoriously enigmatic) but mostly it’s not so hard.

Being ready to pick and eat, however, is not the same thing as being ripe, and this is a matter of great confusion among even some experienced gardeners, so I’ll plant a few ideas here that might help. Or make you more confused. I don’t know, I can’t think in this heat either.

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Q&A: Why do my cucumber and zucchini plants wilt?

One Spotted and multiple Striped Cucumber Beetles, feeding on overripe pumpkin. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Q: Last summer I had cucumbers and zucchini wilting and dying even though I’m pretty certain I didn’t have root rot or squash vine borer. What should I try this year so I can hopefully get a harvest?

A: Bacterial wilt disease, transmitted by cucumber beetles is the prime suspect for crop failure in this instance. Both of these garden pests – Striped Cucumber Beetle and Spotted Cucumber Beetle – are native to North America and can cause serious damage to vegetables in the squash/cucumber family, though they can also feed on unrelated fruits, vegetables, and ornamental plants.

Although their feeding causes direct plant damage, the main issue comes from their introduction of one or more plant pathogens. These beetles can transmit diseases like bacterial wilt and viruses, none of which are curable.

Delaying the planting of squash and cucumber transplants until mid-June may evade the host-seeking adults. Until they bloom, cover plants with insect netting or row cover (the former is ideal as it doesn’t trap heat). Bees will need to reach the flowers for pollination, but once the fruits start to develop, plants tend to be less susceptible to infection. Since more than one beetle generation can occur per year, clean-up veggie garden debris in autumn to deny remaining adults overwintering shelter.

For now, ‘County Fair’ is the only available variety resistant to bacterial wilt. This pickling cucumber is parthenocarpic– it produces mostly female flowers that don’t require pollination to set fruit. The Cucumber Beetles page at the Home & Garden Information Center has more information about these insects and their management.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. Read more by Miri.

Send home gardening questions to Ask Extension at the Home & Garden Information Center

Outsmart Squash Vine Borers This Season – Featured Video

Do your squash plants look wilted in the summer? There could be an invisible enemy larva eating your plant stems from the inside out. And worse yet, typically there is more than one miner inside!

This troubling pest, squash vine borer, seems to hit everyone’s garden in the eastern United States! The borer pest is very hard to control since targeting the egg-laying clearwing moth is like throwing darts in the night. Honestly, it is best to plant squash plants at different time intervals to increase your chance of missing the egg-laying time. Early transplant squash can beat out the egg layers and then late season squash can miss them.

Plan your garden accordingly this year, and you may be able to avoid most of the vine borer problems!

HGIC Website: Squash Vine Borers

Joyce Browning Horticulturist, Master Gardener Coordinator Video credit: Bethany Evans Longwood Gardens Professional Gardener Program Alumni; CPH

Plants not behaving as expected: vegetable garden edition

Two of the vegetable crops I grew this year are known for loving the heat: okra and eggplant. I grow eggplant in pots on my deck, to avoid flea beetle infestation, and okra directly in the ground in my community garden plot. Both of them produced adequately over the summer. Now it’s fall; we’re having days in the 70s and nights in the 50s, and there are fewer hours of sunlight in the day. Time to pull the summer crops, right?

Except – boom! Both the okra and the eggplant are going gangbusters. More flowers, more fruits than in the hot summer months, by far.

‘Bride’ eggplant on a cool autumn morning

So why aren’t these plants following the rulebook? Do they not know how to read? Or have the rules changed?

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Squash vine borers and squash bugs: two garden villains!

My squash and zucchini have been breeding grounds for these two garden pests in past years. They also have confused me because I tend to conflate the two or have mixed up which one I’m searching for information on online. This year, despite taking more steps to combat both of these evil-doers, my garden still took major hits from this duo.

In anticipation of this insect onslaught, I took the following extra steps:

  • I kept the young squash and zucchini plants under floating row cover until they flowered. I uncovered then so that pollinators could get in and do their thing. I potentially could have kept them under cover longer if I manually pollinated, but the plants were growing beyond the cover structure I made, so it was time.
  • I wrapped foil around the lower stems of the plants as HGIC suggests to prevent egg-laying.
  • I searched for and removed more regularly squash bug eggs found under the leaves.
  • I planted these crops in a bed that had NOT yet been used for squash or zucchini and therefore hopefully would not contain overwintering vine borers in the soil.
  • I planted yellow squash, zucchini, and, HERE COMES A NEW CHALLENGER: TROMBONCINO SQUASH! The tromboncino variety is supposed to be vine-borer resistant.

The following is my garden’s tale of woe, and my future plans for growing a squash bug and squash vine borer-free garden.

Let’s start with the one that has been the most visible to me, the squash bug.

Squash bug

For the past few years, I’ve been seeing these guys’ eggs on the undersides of my squash, zucchini, and cucumber plants. When I find them, I tear off the small section of the leaf, smash ’em between my fingers, and chuck them away. I kept doing this, but kept finding more this year. I’m sure tons of the eggs got past me.

Confirming that notion, I did later catch these nymphs having a party on my plants.

Squash bug nymphs
Squash bug and eggs

In my garden at least, I don’t believe the squash bugs are the main villain destroying my squash and zucchini crop. I saw some stippling on the leaves here and there, but nothing that seemed to do severe damage.

Squash bug and stippling on leaf
Squash bug and stippling on leaf – this was about the worst damage I saw like this.

One of my later tromboncino fruits had a ton of superficial damage on it. My guess it is from the squash bugs. They didn’t touch any other tromboncino fruits, and this particular one was closer to ground level, while most of the rest of my tromboncino crop was high in the trellis. Are these guys afraid of heights?

Squash Vine Borer

Previously, in my gardening efforts, I’ve had zucchini and squash plants succumb to the squash vine borer, and I took several steps to avoid them again this year, but to no avail. I’m sorry to say, both our zucchini and squash plants grew large and healthy, produced a round of solid fruits, then quickly wilted and died within a couple weeks of each other.

Tromboncino squash on trellis
Tromboncino squash climbing up it’s trellis, making fruit, and not worrying about any bugs.

I did not see any adult vine borer moths, but I found a big fat larva in the dead plant’s stem. I tore out the dead/dying plants.

While yellow squash and zucchini were out for the count, the tromboncino kept on truckin’ and had no issues so far with either of the nasty bugs other than the one damaged fruit.

What else can I do?

There are more means of combating these bugs if I decide to do battle with these villains again:

For squash vine borers (info mainly from the HGIC page):

  • Adjust the timing of planting. Planting early or late in the season to attempt to avoid the life cycle of the vine borer. Or, plant in succession; stagger when we plant so if some crops get taken out, you still have another coming along with more fruit and another chance at success.
  • Do surgery on the stems of the plant you fear is infested, rip out any larva, and mound up dirt over wounded stems to induce supplemental rooting.
  • Spray lower stems with spinosad or pyrethrum.
  • Spray lower plants stems and base of plant with pyrethrins when adults are flying (mid-late May). Repeat 14 days later. Or sprinkle diatomaceous earth on lower stems. 
  • Bt (Bacillus thuringiensis) or beneficial nematode Stinernema carpocapsae can be injected into wound to kill borers.
  • Seal up infested vines in plastic bag before larvae pupate (break life cycle).
  • Plant resistant crops: Butternut and cushaw are resistant; yellow crookneck is less susceptible than zucchini. (I went for the tromboninos).

For Squash bugs (info mainly from the HGIC page):

  • Neem, horticultural oil, and insecticidal soap are effective when sprayed directly on nymphs. Adults are very difficult to kill with the insecticides available to home gardeners.
  • Trap adults and nymphs by placing boards near host plants under which they will hide. Lift boards and destroy bugs in the morning.
  • Bugs also hide under mulch. When numbers are high, mulch may need to be removed.
  • Removing all plant debris at the end of the growing season is essential.
  • Check seed catalogs for cultivars of summer and winter squash that are resistant to squash bugs.

What will I actually do?

I’m gonna give up!

This is at least the third year in a row with a similar story for the yellow squash and zucchini in my garden, and I think I’m done with regular yellow squash and zucchini for a bit. There are more things I could do to mitigate the problem, but I’m tired of providing food for these buggers, and I’m not into high-maintenance gardening, so I’m gonna call it quits on those crops for now.

Besides, the vine-borer-resistant tromboncino squash crop I tried this year has excelled, and it cooks and eats pretty much like its susceptible cousin crops. I plan to keep going with tromboncino. Maybe a year or two without fodder for these bugs will break the cycle and allow them time to die off or move elsewhere.

Here are two great videos on both of these problem bugs:

Feel free to take a look at my posts from last year’s growing season.

Dan Adler
HGIC Web Support and Video Production